1 //===- SimplifyLibCalls.cpp - Optimize specific well-known library calls --===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by Reid Spencer and is distributed under the
6 // University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements a module pass that applies a variety of small
11 // optimizations for calls to specific well-known function calls (e.g. runtime
12 // library functions). For example, a call to the function "exit(3)" that
13 // occurs within the main() function can be transformed into a simple "return 3"
14 // instruction. Any optimization that takes this form (replace call to library
15 // function with simpler code that provides the same result) belongs in this
18 //===----------------------------------------------------------------------===//
20 #define DEBUG_TYPE "simplify-libcalls"
21 #include "llvm/Constants.h"
22 #include "llvm/DerivedTypes.h"
23 #include "llvm/Instructions.h"
24 #include "llvm/Module.h"
25 #include "llvm/Pass.h"
26 #include "llvm/ADT/hash_map"
27 #include "llvm/ADT/Statistic.h"
28 #include "llvm/Config/config.h"
29 #include "llvm/Support/Debug.h"
30 #include "llvm/Target/TargetData.h"
31 #include "llvm/Transforms/IPO.h"
36 /// This statistic keeps track of the total number of library calls that have
37 /// been simplified regardless of which call it is.
38 Statistic<> SimplifiedLibCalls("simplify-libcalls",
39 "Number of library calls simplified");
41 // Forward declarations
42 class LibCallOptimization;
43 class SimplifyLibCalls;
45 /// This list is populated by the constructor for LibCallOptimization class.
46 /// Therefore all subclasses are registered here at static initialization time
47 /// and this list is what the SimplifyLibCalls pass uses to apply the individual
48 /// optimizations to the call sites.
49 /// @brief The list of optimizations deriving from LibCallOptimization
50 static LibCallOptimization *OptList = 0;
52 /// This class is the abstract base class for the set of optimizations that
53 /// corresponds to one library call. The SimplifyLibCalls pass will call the
54 /// ValidateCalledFunction method to ask the optimization if a given Function
55 /// is the kind that the optimization can handle. If the subclass returns true,
56 /// then SImplifyLibCalls will also call the OptimizeCall method to perform,
57 /// or attempt to perform, the optimization(s) for the library call. Otherwise,
58 /// OptimizeCall won't be called. Subclasses are responsible for providing the
59 /// name of the library call (strlen, strcpy, etc.) to the LibCallOptimization
60 /// constructor. This is used to efficiently select which call instructions to
61 /// optimize. The criteria for a "lib call" is "anything with well known
62 /// semantics", typically a library function that is defined by an international
63 /// standard. Because the semantics are well known, the optimizations can
64 /// generally short-circuit actually calling the function if there's a simpler
65 /// way (e.g. strlen(X) can be reduced to a constant if X is a constant global).
66 /// @brief Base class for library call optimizations
67 class LibCallOptimization {
68 LibCallOptimization **Prev, *Next;
69 const char *FunctionName; ///< Name of the library call we optimize
71 Statistic<> occurrences; ///< debug statistic (-debug-only=simplify-libcalls)
74 /// The \p fname argument must be the name of the library function being
75 /// optimized by the subclass.
76 /// @brief Constructor that registers the optimization.
77 LibCallOptimization(const char *FName, const char *Description)
80 , occurrences("simplify-libcalls", Description)
83 // Register this optimizer in the list of optimizations.
87 if (Next) Next->Prev = &Next;
90 /// getNext - All libcall optimizations are chained together into a list,
91 /// return the next one in the list.
92 LibCallOptimization *getNext() { return Next; }
94 /// @brief Deregister from the optlist
95 virtual ~LibCallOptimization() {
97 if (Next) Next->Prev = Prev;
100 /// The implementation of this function in subclasses should determine if
101 /// \p F is suitable for the optimization. This method is called by
102 /// SimplifyLibCalls::runOnModule to short circuit visiting all the call
103 /// sites of such a function if that function is not suitable in the first
104 /// place. If the called function is suitabe, this method should return true;
105 /// false, otherwise. This function should also perform any lazy
106 /// initialization that the LibCallOptimization needs to do, if its to return
107 /// true. This avoids doing initialization until the optimizer is actually
108 /// going to be called upon to do some optimization.
109 /// @brief Determine if the function is suitable for optimization
110 virtual bool ValidateCalledFunction(
111 const Function* F, ///< The function that is the target of call sites
112 SimplifyLibCalls& SLC ///< The pass object invoking us
115 /// The implementations of this function in subclasses is the heart of the
116 /// SimplifyLibCalls algorithm. Sublcasses of this class implement
117 /// OptimizeCall to determine if (a) the conditions are right for optimizing
118 /// the call and (b) to perform the optimization. If an action is taken
119 /// against ci, the subclass is responsible for returning true and ensuring
120 /// that ci is erased from its parent.
121 /// @brief Optimize a call, if possible.
122 virtual bool OptimizeCall(
123 CallInst* ci, ///< The call instruction that should be optimized.
124 SimplifyLibCalls& SLC ///< The pass object invoking us
127 /// @brief Get the name of the library call being optimized
128 const char *getFunctionName() const { return FunctionName; }
130 /// @brief Called by SimplifyLibCalls to update the occurrences statistic.
133 DEBUG(++occurrences);
138 /// This class is an LLVM Pass that applies each of the LibCallOptimization
139 /// instances to all the call sites in a module, relatively efficiently. The
140 /// purpose of this pass is to provide optimizations for calls to well-known
141 /// functions with well-known semantics, such as those in the c library. The
142 /// class provides the basic infrastructure for handling runOnModule. Whenever
143 /// this pass finds a function call, it asks the appropriate optimizer to
144 /// validate the call (ValidateLibraryCall). If it is validated, then
145 /// the OptimizeCall method is also called.
146 /// @brief A ModulePass for optimizing well-known function calls.
147 class SimplifyLibCalls : public ModulePass {
149 /// We need some target data for accurate signature details that are
150 /// target dependent. So we require target data in our AnalysisUsage.
151 /// @brief Require TargetData from AnalysisUsage.
152 virtual void getAnalysisUsage(AnalysisUsage& Info) const {
153 // Ask that the TargetData analysis be performed before us so we can use
155 Info.addRequired<TargetData>();
158 /// For this pass, process all of the function calls in the module, calling
159 /// ValidateLibraryCall and OptimizeCall as appropriate.
160 /// @brief Run all the lib call optimizations on a Module.
161 virtual bool runOnModule(Module &M) {
165 hash_map<std::string, LibCallOptimization*> OptznMap;
166 for (LibCallOptimization *Optzn = OptList; Optzn; Optzn = Optzn->getNext())
167 OptznMap[Optzn->getFunctionName()] = Optzn;
169 // The call optimizations can be recursive. That is, the optimization might
170 // generate a call to another function which can also be optimized. This way
171 // we make the LibCallOptimization instances very specific to the case they
172 // handle. It also means we need to keep running over the function calls in
173 // the module until we don't get any more optimizations possible.
174 bool found_optimization = false;
176 found_optimization = false;
177 for (Module::iterator FI = M.begin(), FE = M.end(); FI != FE; ++FI) {
178 // All the "well-known" functions are external and have external linkage
179 // because they live in a runtime library somewhere and were (probably)
180 // not compiled by LLVM. So, we only act on external functions that
181 // have external linkage and non-empty uses.
182 if (!FI->isExternal() || !FI->hasExternalLinkage() || FI->use_empty())
185 // Get the optimization class that pertains to this function
186 hash_map<std::string, LibCallOptimization*>::iterator OMI =
187 OptznMap.find(FI->getName());
188 if (OMI == OptznMap.end()) continue;
190 LibCallOptimization *CO = OMI->second;
192 // Make sure the called function is suitable for the optimization
193 if (!CO->ValidateCalledFunction(FI, *this))
196 // Loop over each of the uses of the function
197 for (Value::use_iterator UI = FI->use_begin(), UE = FI->use_end();
199 // If the use of the function is a call instruction
200 if (CallInst* CI = dyn_cast<CallInst>(*UI++)) {
201 // Do the optimization on the LibCallOptimization.
202 if (CO->OptimizeCall(CI, *this)) {
203 ++SimplifiedLibCalls;
204 found_optimization = result = true;
210 } while (found_optimization);
215 /// @brief Return the *current* module we're working on.
216 Module* getModule() const { return M; }
218 /// @brief Return the *current* target data for the module we're working on.
219 TargetData* getTargetData() const { return TD; }
221 /// @brief Return the size_t type -- syntactic shortcut
222 const Type* getIntPtrType() const { return TD->getIntPtrType(); }
224 /// @brief Return a Function* for the fputc libcall
225 Function* get_fputc(const Type* FILEptr_type) {
227 fputc_func = M->getOrInsertFunction("fputc", Type::IntTy, Type::IntTy,
232 /// @brief Return a Function* for the fwrite libcall
233 Function* get_fwrite(const Type* FILEptr_type) {
235 fwrite_func = M->getOrInsertFunction("fwrite", TD->getIntPtrType(),
236 PointerType::get(Type::SByteTy),
243 /// @brief Return a Function* for the sqrt libcall
244 Function* get_sqrt() {
246 sqrt_func = M->getOrInsertFunction("sqrt", Type::DoubleTy,
247 Type::DoubleTy, NULL);
251 /// @brief Return a Function* for the strlen libcall
252 Function* get_strcpy() {
254 strcpy_func = M->getOrInsertFunction("strcpy",
255 PointerType::get(Type::SByteTy),
256 PointerType::get(Type::SByteTy),
257 PointerType::get(Type::SByteTy),
262 /// @brief Return a Function* for the strlen libcall
263 Function* get_strlen() {
265 strlen_func = M->getOrInsertFunction("strlen", TD->getIntPtrType(),
266 PointerType::get(Type::SByteTy),
271 /// @brief Return a Function* for the memchr libcall
272 Function* get_memchr() {
274 memchr_func = M->getOrInsertFunction("memchr",
275 PointerType::get(Type::SByteTy),
276 PointerType::get(Type::SByteTy),
277 Type::IntTy, TD->getIntPtrType(),
282 /// @brief Return a Function* for the memcpy libcall
283 Function* get_memcpy() {
285 const Type *SBP = PointerType::get(Type::SByteTy);
286 const char *N = TD->getIntPtrType() == Type::UIntTy ?
287 "llvm.memcpy.i32" : "llvm.memcpy.i64";
288 memcpy_func = M->getOrInsertFunction(N, Type::VoidTy, SBP, SBP,
289 TD->getIntPtrType(), Type::UIntTy,
295 Function *getUnaryFloatFunction(const char *Name, Function *&Cache) {
297 Cache = M->getOrInsertFunction(Name, Type::FloatTy, Type::FloatTy, NULL);
301 Function *get_floorf() { return getUnaryFloatFunction("floorf", floorf_func);}
302 Function *get_ceilf() { return getUnaryFloatFunction( "ceilf", ceilf_func);}
303 Function *get_roundf() { return getUnaryFloatFunction("roundf", roundf_func);}
304 Function *get_rintf() { return getUnaryFloatFunction( "rintf", rintf_func);}
305 Function *get_nearbyintf() { return getUnaryFloatFunction("nearbyintf",
308 /// @brief Reset our cached data for a new Module
309 void reset(Module& mod) {
311 TD = &getAnalysis<TargetData>();
327 /// Caches for function pointers.
328 Function *fputc_func, *fwrite_func;
329 Function *memcpy_func, *memchr_func;
331 Function *strcpy_func, *strlen_func;
332 Function *floorf_func, *ceilf_func, *roundf_func;
333 Function *rintf_func, *nearbyintf_func;
334 Module *M; ///< Cached Module
335 TargetData *TD; ///< Cached TargetData
339 RegisterOpt<SimplifyLibCalls>
340 X("simplify-libcalls","Simplify well-known library calls");
342 } // anonymous namespace
344 // The only public symbol in this file which just instantiates the pass object
345 ModulePass *llvm::createSimplifyLibCallsPass() {
346 return new SimplifyLibCalls();
349 // Classes below here, in the anonymous namespace, are all subclasses of the
350 // LibCallOptimization class, each implementing all optimizations possible for a
351 // single well-known library call. Each has a static singleton instance that
352 // auto registers it into the "optlist" global above.
355 // Forward declare utility functions.
356 bool getConstantStringLength(Value* V, uint64_t& len, ConstantArray** A = 0 );
357 Value *CastToCStr(Value *V, Instruction &IP);
359 /// This LibCallOptimization will find instances of a call to "exit" that occurs
360 /// within the "main" function and change it to a simple "ret" instruction with
361 /// the same value passed to the exit function. When this is done, it splits the
362 /// basic block at the exit(3) call and deletes the call instruction.
363 /// @brief Replace calls to exit in main with a simple return
364 struct ExitInMainOptimization : public LibCallOptimization {
365 ExitInMainOptimization() : LibCallOptimization("exit",
366 "Number of 'exit' calls simplified") {}
368 // Make sure the called function looks like exit (int argument, int return
369 // type, external linkage, not varargs).
370 virtual bool ValidateCalledFunction(const Function *F, SimplifyLibCalls &SLC){
371 return F->arg_size() >= 1 && F->arg_begin()->getType()->isInteger();
374 virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& SLC) {
375 // To be careful, we check that the call to exit is coming from "main", that
376 // main has external linkage, and the return type of main and the argument
377 // to exit have the same type.
378 Function *from = ci->getParent()->getParent();
379 if (from->hasExternalLinkage())
380 if (from->getReturnType() == ci->getOperand(1)->getType())
381 if (from->getName() == "main") {
382 // Okay, time to actually do the optimization. First, get the basic
383 // block of the call instruction
384 BasicBlock* bb = ci->getParent();
386 // Create a return instruction that we'll replace the call with.
387 // Note that the argument of the return is the argument of the call
389 new ReturnInst(ci->getOperand(1), ci);
391 // Split the block at the call instruction which places it in a new
393 bb->splitBasicBlock(ci);
395 // The block split caused a branch instruction to be inserted into
396 // the end of the original block, right after the return instruction
397 // that we put there. That's not a valid block, so delete the branch
399 bb->getInstList().pop_back();
401 // Now we can finally get rid of the call instruction which now lives
402 // in the new basic block.
403 ci->eraseFromParent();
405 // Optimization succeeded, return true.
408 // We didn't pass the criteria for this optimization so return false
411 } ExitInMainOptimizer;
413 /// This LibCallOptimization will simplify a call to the strcat library
414 /// function. The simplification is possible only if the string being
415 /// concatenated is a constant array or a constant expression that results in
416 /// a constant string. In this case we can replace it with strlen + llvm.memcpy
417 /// of the constant string. Both of these calls are further reduced, if possible
418 /// on subsequent passes.
419 /// @brief Simplify the strcat library function.
420 struct StrCatOptimization : public LibCallOptimization {
422 /// @brief Default constructor
423 StrCatOptimization() : LibCallOptimization("strcat",
424 "Number of 'strcat' calls simplified") {}
428 /// @brief Make sure that the "strcat" function has the right prototype
429 virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC){
430 if (f->getReturnType() == PointerType::get(Type::SByteTy))
431 if (f->arg_size() == 2)
433 Function::const_arg_iterator AI = f->arg_begin();
434 if (AI++->getType() == PointerType::get(Type::SByteTy))
435 if (AI->getType() == PointerType::get(Type::SByteTy))
437 // Indicate this is a suitable call type.
444 /// @brief Optimize the strcat library function
445 virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& SLC) {
446 // Extract some information from the instruction
447 Value* dest = ci->getOperand(1);
448 Value* src = ci->getOperand(2);
450 // Extract the initializer (while making numerous checks) from the
451 // source operand of the call to strcat. If we get null back, one of
452 // a variety of checks in get_GVInitializer failed
454 if (!getConstantStringLength(src,len))
457 // Handle the simple, do-nothing case
459 ci->replaceAllUsesWith(dest);
460 ci->eraseFromParent();
464 // Increment the length because we actually want to memcpy the null
465 // terminator as well.
468 // We need to find the end of the destination string. That's where the
469 // memory is to be moved to. We just generate a call to strlen (further
470 // optimized in another pass). Note that the SLC.get_strlen() call
471 // caches the Function* for us.
472 CallInst* strlen_inst =
473 new CallInst(SLC.get_strlen(), dest, dest->getName()+".len",ci);
475 // Now that we have the destination's length, we must index into the
476 // destination's pointer to get the actual memcpy destination (end of
477 // the string .. we're concatenating).
478 std::vector<Value*> idx;
479 idx.push_back(strlen_inst);
480 GetElementPtrInst* gep =
481 new GetElementPtrInst(dest,idx,dest->getName()+".indexed",ci);
483 // We have enough information to now generate the memcpy call to
484 // do the concatenation for us.
485 std::vector<Value*> vals;
486 vals.push_back(gep); // destination
487 vals.push_back(ci->getOperand(2)); // source
488 vals.push_back(ConstantUInt::get(SLC.getIntPtrType(),len)); // length
489 vals.push_back(ConstantUInt::get(Type::UIntTy,1)); // alignment
490 new CallInst(SLC.get_memcpy(), vals, "", ci);
492 // Finally, substitute the first operand of the strcat call for the
493 // strcat call itself since strcat returns its first operand; and,
494 // kill the strcat CallInst.
495 ci->replaceAllUsesWith(dest);
496 ci->eraseFromParent();
501 /// This LibCallOptimization will simplify a call to the strchr library
502 /// function. It optimizes out cases where the arguments are both constant
503 /// and the result can be determined statically.
504 /// @brief Simplify the strcmp library function.
505 struct StrChrOptimization : public LibCallOptimization {
507 StrChrOptimization() : LibCallOptimization("strchr",
508 "Number of 'strchr' calls simplified") {}
510 /// @brief Make sure that the "strchr" function has the right prototype
511 virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC){
512 if (f->getReturnType() == PointerType::get(Type::SByteTy) &&
518 /// @brief Perform the strchr optimizations
519 virtual bool OptimizeCall(CallInst *ci, SimplifyLibCalls &SLC) {
520 // If there aren't three operands, bail
521 if (ci->getNumOperands() != 3)
524 // Check that the first argument to strchr is a constant array of sbyte.
525 // If it is, get the length and data, otherwise return false.
528 if (!getConstantStringLength(ci->getOperand(1),len,&CA))
531 // Check that the second argument to strchr is a constant int, return false
533 ConstantSInt* CSI = dyn_cast<ConstantSInt>(ci->getOperand(2));
535 // Just lower this to memchr since we know the length of the string as
537 Function* f = SLC.get_memchr();
538 std::vector<Value*> args;
539 args.push_back(ci->getOperand(1));
540 args.push_back(ci->getOperand(2));
541 args.push_back(ConstantUInt::get(SLC.getIntPtrType(),len));
542 ci->replaceAllUsesWith( new CallInst(f,args,ci->getName(),ci));
543 ci->eraseFromParent();
547 // Get the character we're looking for
548 int64_t chr = CSI->getValue();
550 // Compute the offset
552 bool char_found = false;
553 for (uint64_t i = 0; i < len; ++i) {
554 if (ConstantSInt* CI = dyn_cast<ConstantSInt>(CA->getOperand(i))) {
555 // Check for the null terminator
556 if (CI->isNullValue())
557 break; // we found end of string
558 else if (CI->getValue() == chr) {
566 // strchr(s,c) -> offset_of_in(c,s)
567 // (if c is a constant integer and s is a constant string)
569 std::vector<Value*> indices;
570 indices.push_back(ConstantUInt::get(Type::ULongTy,offset));
571 GetElementPtrInst* GEP = new GetElementPtrInst(ci->getOperand(1),indices,
572 ci->getOperand(1)->getName()+".strchr",ci);
573 ci->replaceAllUsesWith(GEP);
575 ci->replaceAllUsesWith(
576 ConstantPointerNull::get(PointerType::get(Type::SByteTy)));
578 ci->eraseFromParent();
583 /// This LibCallOptimization will simplify a call to the strcmp library
584 /// function. It optimizes out cases where one or both arguments are constant
585 /// and the result can be determined statically.
586 /// @brief Simplify the strcmp library function.
587 struct StrCmpOptimization : public LibCallOptimization {
589 StrCmpOptimization() : LibCallOptimization("strcmp",
590 "Number of 'strcmp' calls simplified") {}
592 /// @brief Make sure that the "strcmp" function has the right prototype
593 virtual bool ValidateCalledFunction(const Function *F, SimplifyLibCalls &SLC){
594 return F->getReturnType() == Type::IntTy && F->arg_size() == 2;
597 /// @brief Perform the strcmp optimization
598 virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& SLC) {
599 // First, check to see if src and destination are the same. If they are,
600 // then the optimization is to replace the CallInst with a constant 0
601 // because the call is a no-op.
602 Value* s1 = ci->getOperand(1);
603 Value* s2 = ci->getOperand(2);
606 ci->replaceAllUsesWith(ConstantInt::get(Type::IntTy,0));
607 ci->eraseFromParent();
611 bool isstr_1 = false;
614 if (getConstantStringLength(s1,len_1,&A1)) {
617 // strcmp("",x) -> *x
619 new LoadInst(CastToCStr(s2,*ci), ci->getName()+".load",ci);
621 new CastInst(load,Type::IntTy,ci->getName()+".int",ci);
622 ci->replaceAllUsesWith(cast);
623 ci->eraseFromParent();
628 bool isstr_2 = false;
631 if (getConstantStringLength(s2, len_2, &A2)) {
634 // strcmp(x,"") -> *x
636 new LoadInst(CastToCStr(s1,*ci),ci->getName()+".val",ci);
638 new CastInst(load,Type::IntTy,ci->getName()+".int",ci);
639 ci->replaceAllUsesWith(cast);
640 ci->eraseFromParent();
645 if (isstr_1 && isstr_2) {
646 // strcmp(x,y) -> cnst (if both x and y are constant strings)
647 std::string str1 = A1->getAsString();
648 std::string str2 = A2->getAsString();
649 int result = strcmp(str1.c_str(), str2.c_str());
650 ci->replaceAllUsesWith(ConstantSInt::get(Type::IntTy,result));
651 ci->eraseFromParent();
658 /// This LibCallOptimization will simplify a call to the strncmp library
659 /// function. It optimizes out cases where one or both arguments are constant
660 /// and the result can be determined statically.
661 /// @brief Simplify the strncmp library function.
662 struct StrNCmpOptimization : public LibCallOptimization {
664 StrNCmpOptimization() : LibCallOptimization("strncmp",
665 "Number of 'strncmp' calls simplified") {}
667 /// @brief Make sure that the "strncmp" function has the right prototype
668 virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC){
669 if (f->getReturnType() == Type::IntTy && f->arg_size() == 3)
674 /// @brief Perform the strncpy optimization
675 virtual bool OptimizeCall(CallInst *ci, SimplifyLibCalls &SLC) {
676 // First, check to see if src and destination are the same. If they are,
677 // then the optimization is to replace the CallInst with a constant 0
678 // because the call is a no-op.
679 Value* s1 = ci->getOperand(1);
680 Value* s2 = ci->getOperand(2);
682 // strncmp(x,x,l) -> 0
683 ci->replaceAllUsesWith(ConstantInt::get(Type::IntTy,0));
684 ci->eraseFromParent();
688 // Check the length argument, if it is Constant zero then the strings are
690 uint64_t len_arg = 0;
691 bool len_arg_is_const = false;
692 if (ConstantInt* len_CI = dyn_cast<ConstantInt>(ci->getOperand(3))) {
693 len_arg_is_const = true;
694 len_arg = len_CI->getRawValue();
696 // strncmp(x,y,0) -> 0
697 ci->replaceAllUsesWith(ConstantInt::get(Type::IntTy,0));
698 ci->eraseFromParent();
703 bool isstr_1 = false;
706 if (getConstantStringLength(s1, len_1, &A1)) {
709 // strncmp("",x) -> *x
710 LoadInst* load = new LoadInst(s1,ci->getName()+".load",ci);
712 new CastInst(load,Type::IntTy,ci->getName()+".int",ci);
713 ci->replaceAllUsesWith(cast);
714 ci->eraseFromParent();
719 bool isstr_2 = false;
722 if (getConstantStringLength(s2,len_2,&A2)) {
725 // strncmp(x,"") -> *x
726 LoadInst* load = new LoadInst(s2,ci->getName()+".val",ci);
728 new CastInst(load,Type::IntTy,ci->getName()+".int",ci);
729 ci->replaceAllUsesWith(cast);
730 ci->eraseFromParent();
735 if (isstr_1 && isstr_2 && len_arg_is_const) {
736 // strncmp(x,y,const) -> constant
737 std::string str1 = A1->getAsString();
738 std::string str2 = A2->getAsString();
739 int result = strncmp(str1.c_str(), str2.c_str(), len_arg);
740 ci->replaceAllUsesWith(ConstantSInt::get(Type::IntTy,result));
741 ci->eraseFromParent();
748 /// This LibCallOptimization will simplify a call to the strcpy library
749 /// function. Two optimizations are possible:
750 /// (1) If src and dest are the same and not volatile, just return dest
751 /// (2) If the src is a constant then we can convert to llvm.memmove
752 /// @brief Simplify the strcpy library function.
753 struct StrCpyOptimization : public LibCallOptimization {
755 StrCpyOptimization() : LibCallOptimization("strcpy",
756 "Number of 'strcpy' calls simplified") {}
758 /// @brief Make sure that the "strcpy" function has the right prototype
759 virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC){
760 if (f->getReturnType() == PointerType::get(Type::SByteTy))
761 if (f->arg_size() == 2) {
762 Function::const_arg_iterator AI = f->arg_begin();
763 if (AI++->getType() == PointerType::get(Type::SByteTy))
764 if (AI->getType() == PointerType::get(Type::SByteTy)) {
765 // Indicate this is a suitable call type.
772 /// @brief Perform the strcpy optimization
773 virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& SLC) {
774 // First, check to see if src and destination are the same. If they are,
775 // then the optimization is to replace the CallInst with the destination
776 // because the call is a no-op. Note that this corresponds to the
777 // degenerate strcpy(X,X) case which should have "undefined" results
778 // according to the C specification. However, it occurs sometimes and
779 // we optimize it as a no-op.
780 Value* dest = ci->getOperand(1);
781 Value* src = ci->getOperand(2);
783 ci->replaceAllUsesWith(dest);
784 ci->eraseFromParent();
788 // Get the length of the constant string referenced by the second operand,
789 // the "src" parameter. Fail the optimization if we can't get the length
790 // (note that getConstantStringLength does lots of checks to make sure this
793 if (!getConstantStringLength(ci->getOperand(2),len))
796 // If the constant string's length is zero we can optimize this by just
797 // doing a store of 0 at the first byte of the destination
799 new StoreInst(ConstantInt::get(Type::SByteTy,0),ci->getOperand(1),ci);
800 ci->replaceAllUsesWith(dest);
801 ci->eraseFromParent();
805 // Increment the length because we actually want to memcpy the null
806 // terminator as well.
809 // We have enough information to now generate the memcpy call to
810 // do the concatenation for us.
811 std::vector<Value*> vals;
812 vals.push_back(dest); // destination
813 vals.push_back(src); // source
814 vals.push_back(ConstantUInt::get(SLC.getIntPtrType(),len)); // length
815 vals.push_back(ConstantUInt::get(Type::UIntTy,1)); // alignment
816 new CallInst(SLC.get_memcpy(), vals, "", ci);
818 // Finally, substitute the first operand of the strcat call for the
819 // strcat call itself since strcat returns its first operand; and,
820 // kill the strcat CallInst.
821 ci->replaceAllUsesWith(dest);
822 ci->eraseFromParent();
827 /// This LibCallOptimization will simplify a call to the strlen library
828 /// function by replacing it with a constant value if the string provided to
829 /// it is a constant array.
830 /// @brief Simplify the strlen library function.
831 struct StrLenOptimization : public LibCallOptimization {
832 StrLenOptimization() : LibCallOptimization("strlen",
833 "Number of 'strlen' calls simplified") {}
835 /// @brief Make sure that the "strlen" function has the right prototype
836 virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC)
838 if (f->getReturnType() == SLC.getTargetData()->getIntPtrType())
839 if (f->arg_size() == 1)
840 if (Function::const_arg_iterator AI = f->arg_begin())
841 if (AI->getType() == PointerType::get(Type::SByteTy))
846 /// @brief Perform the strlen optimization
847 virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& SLC)
849 // Make sure we're dealing with an sbyte* here.
850 Value* str = ci->getOperand(1);
851 if (str->getType() != PointerType::get(Type::SByteTy))
854 // Does the call to strlen have exactly one use?
856 // Is that single use a binary operator?
857 if (BinaryOperator* bop = dyn_cast<BinaryOperator>(ci->use_back()))
858 // Is it compared against a constant integer?
859 if (ConstantInt* CI = dyn_cast<ConstantInt>(bop->getOperand(1)))
861 // Get the value the strlen result is compared to
862 uint64_t val = CI->getRawValue();
864 // If its compared against length 0 with == or !=
866 (bop->getOpcode() == Instruction::SetEQ ||
867 bop->getOpcode() == Instruction::SetNE))
869 // strlen(x) != 0 -> *x != 0
870 // strlen(x) == 0 -> *x == 0
871 LoadInst* load = new LoadInst(str,str->getName()+".first",ci);
872 BinaryOperator* rbop = BinaryOperator::create(bop->getOpcode(),
873 load, ConstantSInt::get(Type::SByteTy,0),
874 bop->getName()+".strlen", ci);
875 bop->replaceAllUsesWith(rbop);
876 bop->eraseFromParent();
877 ci->eraseFromParent();
882 // Get the length of the constant string operand
884 if (!getConstantStringLength(ci->getOperand(1),len))
887 // strlen("xyz") -> 3 (for example)
888 const Type *Ty = SLC.getTargetData()->getIntPtrType();
890 ci->replaceAllUsesWith(ConstantSInt::get(Ty, len));
892 ci->replaceAllUsesWith(ConstantUInt::get(Ty, len));
894 ci->eraseFromParent();
899 /// IsOnlyUsedInEqualsComparison - Return true if it only matters that the value
900 /// is equal or not-equal to zero.
901 static bool IsOnlyUsedInEqualsZeroComparison(Instruction *I) {
902 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
904 Instruction *User = cast<Instruction>(*UI);
905 if (User->getOpcode() == Instruction::SetNE ||
906 User->getOpcode() == Instruction::SetEQ) {
907 if (isa<Constant>(User->getOperand(1)) &&
908 cast<Constant>(User->getOperand(1))->isNullValue())
910 } else if (CastInst *CI = dyn_cast<CastInst>(User))
911 if (CI->getType() == Type::BoolTy)
913 // Unknown instruction.
919 /// This memcmpOptimization will simplify a call to the memcmp library
921 struct memcmpOptimization : public LibCallOptimization {
922 /// @brief Default Constructor
924 : LibCallOptimization("memcmp", "Number of 'memcmp' calls simplified") {}
926 /// @brief Make sure that the "memcmp" function has the right prototype
927 virtual bool ValidateCalledFunction(const Function *F, SimplifyLibCalls &TD) {
928 Function::const_arg_iterator AI = F->arg_begin();
929 if (F->arg_size() != 3 || !isa<PointerType>(AI->getType())) return false;
930 if (!isa<PointerType>((++AI)->getType())) return false;
931 if (!(++AI)->getType()->isInteger()) return false;
932 if (!F->getReturnType()->isInteger()) return false;
936 /// Because of alignment and instruction information that we don't have, we
937 /// leave the bulk of this to the code generators.
939 /// Note that we could do much more if we could force alignment on otherwise
940 /// small aligned allocas, or if we could indicate that loads have a small
942 virtual bool OptimizeCall(CallInst *CI, SimplifyLibCalls &TD) {
943 Value *LHS = CI->getOperand(1), *RHS = CI->getOperand(2);
945 // If the two operands are the same, return zero.
947 // memcmp(s,s,x) -> 0
948 CI->replaceAllUsesWith(Constant::getNullValue(CI->getType()));
949 CI->eraseFromParent();
953 // Make sure we have a constant length.
954 ConstantInt *LenC = dyn_cast<ConstantInt>(CI->getOperand(3));
955 if (!LenC) return false;
956 uint64_t Len = LenC->getRawValue();
958 // If the length is zero, this returns 0.
961 // memcmp(s1,s2,0) -> 0
962 CI->replaceAllUsesWith(Constant::getNullValue(CI->getType()));
963 CI->eraseFromParent();
966 // memcmp(S1,S2,1) -> *(ubyte*)S1 - *(ubyte*)S2
967 const Type *UCharPtr = PointerType::get(Type::UByteTy);
968 CastInst *Op1Cast = new CastInst(LHS, UCharPtr, LHS->getName(), CI);
969 CastInst *Op2Cast = new CastInst(RHS, UCharPtr, RHS->getName(), CI);
970 Value *S1V = new LoadInst(Op1Cast, LHS->getName()+".val", CI);
971 Value *S2V = new LoadInst(Op2Cast, RHS->getName()+".val", CI);
972 Value *RV = BinaryOperator::createSub(S1V, S2V, CI->getName()+".diff",CI);
973 if (RV->getType() != CI->getType())
974 RV = new CastInst(RV, CI->getType(), RV->getName(), CI);
975 CI->replaceAllUsesWith(RV);
976 CI->eraseFromParent();
980 if (IsOnlyUsedInEqualsZeroComparison(CI)) {
981 // TODO: IF both are aligned, use a short load/compare.
983 // memcmp(S1,S2,2) -> S1[0]-S2[0] | S1[1]-S2[1] iff only ==/!= 0 matters
984 const Type *UCharPtr = PointerType::get(Type::UByteTy);
985 CastInst *Op1Cast = new CastInst(LHS, UCharPtr, LHS->getName(), CI);
986 CastInst *Op2Cast = new CastInst(RHS, UCharPtr, RHS->getName(), CI);
987 Value *S1V1 = new LoadInst(Op1Cast, LHS->getName()+".val1", CI);
988 Value *S2V1 = new LoadInst(Op2Cast, RHS->getName()+".val1", CI);
989 Value *D1 = BinaryOperator::createSub(S1V1, S2V1,
990 CI->getName()+".d1", CI);
991 Constant *One = ConstantInt::get(Type::IntTy, 1);
992 Value *G1 = new GetElementPtrInst(Op1Cast, One, "next1v", CI);
993 Value *G2 = new GetElementPtrInst(Op2Cast, One, "next2v", CI);
994 Value *S1V2 = new LoadInst(G1, LHS->getName()+".val2", CI);
995 Value *S2V2 = new LoadInst(G2, RHS->getName()+".val2", CI);
996 Value *D2 = BinaryOperator::createSub(S1V2, S2V2,
997 CI->getName()+".d1", CI);
998 Value *Or = BinaryOperator::createOr(D1, D2, CI->getName()+".res", CI);
999 if (Or->getType() != CI->getType())
1000 Or = new CastInst(Or, CI->getType(), Or->getName(), CI);
1001 CI->replaceAllUsesWith(Or);
1002 CI->eraseFromParent();
1015 /// This LibCallOptimization will simplify a call to the memcpy library
1016 /// function by expanding it out to a single store of size 0, 1, 2, 4, or 8
1017 /// bytes depending on the length of the string and the alignment. Additional
1018 /// optimizations are possible in code generation (sequence of immediate store)
1019 /// @brief Simplify the memcpy library function.
1020 struct LLVMMemCpyMoveOptzn : public LibCallOptimization {
1021 LLVMMemCpyMoveOptzn(const char* fname, const char* desc)
1022 : LibCallOptimization(fname, desc) {}
1024 /// @brief Make sure that the "memcpy" function has the right prototype
1025 virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& TD) {
1026 // Just make sure this has 4 arguments per LLVM spec.
1027 return (f->arg_size() == 4);
1030 /// Because of alignment and instruction information that we don't have, we
1031 /// leave the bulk of this to the code generators. The optimization here just
1032 /// deals with a few degenerate cases where the length of the string and the
1033 /// alignment match the sizes of our intrinsic types so we can do a load and
1034 /// store instead of the memcpy call.
1035 /// @brief Perform the memcpy optimization.
1036 virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& TD) {
1037 // Make sure we have constant int values to work with
1038 ConstantInt* LEN = dyn_cast<ConstantInt>(ci->getOperand(3));
1041 ConstantInt* ALIGN = dyn_cast<ConstantInt>(ci->getOperand(4));
1045 // If the length is larger than the alignment, we can't optimize
1046 uint64_t len = LEN->getRawValue();
1047 uint64_t alignment = ALIGN->getRawValue();
1049 alignment = 1; // Alignment 0 is identity for alignment 1
1050 if (len > alignment)
1053 // Get the type we will cast to, based on size of the string
1054 Value* dest = ci->getOperand(1);
1055 Value* src = ci->getOperand(2);
1060 // memcpy(d,s,0,a) -> noop
1061 ci->eraseFromParent();
1063 case 1: castType = Type::SByteTy; break;
1064 case 2: castType = Type::ShortTy; break;
1065 case 4: castType = Type::IntTy; break;
1066 case 8: castType = Type::LongTy; break;
1071 // Cast source and dest to the right sized primitive and then load/store
1073 new CastInst(src,PointerType::get(castType),src->getName()+".cast",ci);
1074 CastInst* DestCast =
1075 new CastInst(dest,PointerType::get(castType),dest->getName()+".cast",ci);
1076 LoadInst* LI = new LoadInst(SrcCast,SrcCast->getName()+".val",ci);
1077 StoreInst* SI = new StoreInst(LI, DestCast, ci);
1078 ci->eraseFromParent();
1083 /// This LibCallOptimization will simplify a call to the memcpy/memmove library
1085 LLVMMemCpyMoveOptzn LLVMMemCpyOptimizer32("llvm.memcpy.i32",
1086 "Number of 'llvm.memcpy' calls simplified");
1087 LLVMMemCpyMoveOptzn LLVMMemCpyOptimizer64("llvm.memcpy.i64",
1088 "Number of 'llvm.memcpy' calls simplified");
1089 LLVMMemCpyMoveOptzn LLVMMemMoveOptimizer32("llvm.memmove.i32",
1090 "Number of 'llvm.memmove' calls simplified");
1091 LLVMMemCpyMoveOptzn LLVMMemMoveOptimizer64("llvm.memmove.i64",
1092 "Number of 'llvm.memmove' calls simplified");
1094 /// This LibCallOptimization will simplify a call to the memset library
1095 /// function by expanding it out to a single store of size 0, 1, 2, 4, or 8
1096 /// bytes depending on the length argument.
1097 struct LLVMMemSetOptimization : public LibCallOptimization {
1098 /// @brief Default Constructor
1099 LLVMMemSetOptimization(const char *Name) : LibCallOptimization(Name,
1100 "Number of 'llvm.memset' calls simplified") {}
1102 /// @brief Make sure that the "memset" function has the right prototype
1103 virtual bool ValidateCalledFunction(const Function *F, SimplifyLibCalls &TD) {
1104 // Just make sure this has 3 arguments per LLVM spec.
1105 return F->arg_size() == 4;
1108 /// Because of alignment and instruction information that we don't have, we
1109 /// leave the bulk of this to the code generators. The optimization here just
1110 /// deals with a few degenerate cases where the length parameter is constant
1111 /// and the alignment matches the sizes of our intrinsic types so we can do
1112 /// store instead of the memcpy call. Other calls are transformed into the
1113 /// llvm.memset intrinsic.
1114 /// @brief Perform the memset optimization.
1115 virtual bool OptimizeCall(CallInst *ci, SimplifyLibCalls &TD) {
1116 // Make sure we have constant int values to work with
1117 ConstantInt* LEN = dyn_cast<ConstantInt>(ci->getOperand(3));
1120 ConstantInt* ALIGN = dyn_cast<ConstantInt>(ci->getOperand(4));
1124 // Extract the length and alignment
1125 uint64_t len = LEN->getRawValue();
1126 uint64_t alignment = ALIGN->getRawValue();
1128 // Alignment 0 is identity for alignment 1
1132 // If the length is zero, this is a no-op
1134 // memset(d,c,0,a) -> noop
1135 ci->eraseFromParent();
1139 // If the length is larger than the alignment, we can't optimize
1140 if (len > alignment)
1143 // Make sure we have a constant ubyte to work with so we can extract
1144 // the value to be filled.
1145 ConstantUInt* FILL = dyn_cast<ConstantUInt>(ci->getOperand(2));
1148 if (FILL->getType() != Type::UByteTy)
1151 // memset(s,c,n) -> store s, c (for n=1,2,4,8)
1153 // Extract the fill character
1154 uint64_t fill_char = FILL->getValue();
1155 uint64_t fill_value = fill_char;
1157 // Get the type we will cast to, based on size of memory area to fill, and
1158 // and the value we will store there.
1159 Value* dest = ci->getOperand(1);
1163 castType = Type::UByteTy;
1166 castType = Type::UShortTy;
1167 fill_value |= fill_char << 8;
1170 castType = Type::UIntTy;
1171 fill_value |= fill_char << 8 | fill_char << 16 | fill_char << 24;
1174 castType = Type::ULongTy;
1175 fill_value |= fill_char << 8 | fill_char << 16 | fill_char << 24;
1176 fill_value |= fill_char << 32 | fill_char << 40 | fill_char << 48;
1177 fill_value |= fill_char << 56;
1183 // Cast dest to the right sized primitive and then load/store
1184 CastInst* DestCast =
1185 new CastInst(dest,PointerType::get(castType),dest->getName()+".cast",ci);
1186 new StoreInst(ConstantUInt::get(castType,fill_value),DestCast, ci);
1187 ci->eraseFromParent();
1192 LLVMMemSetOptimization MemSet32Optimizer("llvm.memset.i32");
1193 LLVMMemSetOptimization MemSet64Optimizer("llvm.memset.i64");
1196 /// This LibCallOptimization will simplify calls to the "pow" library
1197 /// function. It looks for cases where the result of pow is well known and
1198 /// substitutes the appropriate value.
1199 /// @brief Simplify the pow library function.
1200 struct PowOptimization : public LibCallOptimization {
1202 /// @brief Default Constructor
1203 PowOptimization() : LibCallOptimization("pow",
1204 "Number of 'pow' calls simplified") {}
1206 /// @brief Make sure that the "pow" function has the right prototype
1207 virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC){
1208 // Just make sure this has 2 arguments
1209 return (f->arg_size() == 2);
1212 /// @brief Perform the pow optimization.
1213 virtual bool OptimizeCall(CallInst *ci, SimplifyLibCalls &SLC) {
1214 const Type *Ty = cast<Function>(ci->getOperand(0))->getReturnType();
1215 Value* base = ci->getOperand(1);
1216 Value* expn = ci->getOperand(2);
1217 if (ConstantFP *Op1 = dyn_cast<ConstantFP>(base)) {
1218 double Op1V = Op1->getValue();
1220 // pow(1.0,x) -> 1.0
1221 ci->replaceAllUsesWith(ConstantFP::get(Ty,1.0));
1222 ci->eraseFromParent();
1225 } else if (ConstantFP* Op2 = dyn_cast<ConstantFP>(expn)) {
1226 double Op2V = Op2->getValue();
1228 // pow(x,0.0) -> 1.0
1229 ci->replaceAllUsesWith(ConstantFP::get(Ty,1.0));
1230 ci->eraseFromParent();
1232 } else if (Op2V == 0.5) {
1233 // pow(x,0.5) -> sqrt(x)
1234 CallInst* sqrt_inst = new CallInst(SLC.get_sqrt(), base,
1235 ci->getName()+".pow",ci);
1236 ci->replaceAllUsesWith(sqrt_inst);
1237 ci->eraseFromParent();
1239 } else if (Op2V == 1.0) {
1241 ci->replaceAllUsesWith(base);
1242 ci->eraseFromParent();
1244 } else if (Op2V == -1.0) {
1245 // pow(x,-1.0) -> 1.0/x
1246 BinaryOperator* div_inst= BinaryOperator::createDiv(
1247 ConstantFP::get(Ty,1.0), base, ci->getName()+".pow", ci);
1248 ci->replaceAllUsesWith(div_inst);
1249 ci->eraseFromParent();
1253 return false; // opt failed
1257 /// This LibCallOptimization will simplify calls to the "fprintf" library
1258 /// function. It looks for cases where the result of fprintf is not used and the
1259 /// operation can be reduced to something simpler.
1260 /// @brief Simplify the pow library function.
1261 struct FPrintFOptimization : public LibCallOptimization {
1263 /// @brief Default Constructor
1264 FPrintFOptimization() : LibCallOptimization("fprintf",
1265 "Number of 'fprintf' calls simplified") {}
1267 /// @brief Make sure that the "fprintf" function has the right prototype
1268 virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC){
1269 // Just make sure this has at least 2 arguments
1270 return (f->arg_size() >= 2);
1273 /// @brief Perform the fprintf optimization.
1274 virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& SLC) {
1275 // If the call has more than 3 operands, we can't optimize it
1276 if (ci->getNumOperands() > 4 || ci->getNumOperands() <= 2)
1279 // If the result of the fprintf call is used, none of these optimizations
1281 if (!ci->use_empty())
1284 // All the optimizations depend on the length of the second argument and the
1285 // fact that it is a constant string array. Check that now
1287 ConstantArray* CA = 0;
1288 if (!getConstantStringLength(ci->getOperand(2), len, &CA))
1291 if (ci->getNumOperands() == 3) {
1292 // Make sure there's no % in the constant array
1293 for (unsigned i = 0; i < len; ++i) {
1294 if (ConstantInt* CI = dyn_cast<ConstantInt>(CA->getOperand(i))) {
1295 // Check for the null terminator
1296 if (CI->getRawValue() == '%')
1297 return false; // we found end of string
1303 // fprintf(file,fmt) -> fwrite(fmt,strlen(fmt),file)
1304 const Type* FILEptr_type = ci->getOperand(1)->getType();
1305 Function* fwrite_func = SLC.get_fwrite(FILEptr_type);
1309 // Make sure that the fprintf() and fwrite() functions both take the
1310 // same type of char pointer.
1311 if (ci->getOperand(2)->getType() !=
1312 fwrite_func->getFunctionType()->getParamType(0))
1315 std::vector<Value*> args;
1316 args.push_back(ci->getOperand(2));
1317 args.push_back(ConstantUInt::get(SLC.getIntPtrType(),len));
1318 args.push_back(ConstantUInt::get(SLC.getIntPtrType(),1));
1319 args.push_back(ci->getOperand(1));
1320 new CallInst(fwrite_func,args,ci->getName(),ci);
1321 ci->replaceAllUsesWith(ConstantSInt::get(Type::IntTy,len));
1322 ci->eraseFromParent();
1326 // The remaining optimizations require the format string to be length 2
1331 // The first character has to be a %
1332 if (ConstantInt* CI = dyn_cast<ConstantInt>(CA->getOperand(0)))
1333 if (CI->getRawValue() != '%')
1336 // Get the second character and switch on its value
1337 ConstantInt* CI = dyn_cast<ConstantInt>(CA->getOperand(1));
1338 switch (CI->getRawValue()) {
1342 ConstantArray* CA = 0;
1343 if (!getConstantStringLength(ci->getOperand(3), len, &CA))
1346 // fprintf(file,"%s",str) -> fwrite(fmt,strlen(fmt),1,file)
1347 const Type* FILEptr_type = ci->getOperand(1)->getType();
1348 Function* fwrite_func = SLC.get_fwrite(FILEptr_type);
1351 std::vector<Value*> args;
1352 args.push_back(CastToCStr(ci->getOperand(3), *ci));
1353 args.push_back(ConstantUInt::get(SLC.getIntPtrType(),len));
1354 args.push_back(ConstantUInt::get(SLC.getIntPtrType(),1));
1355 args.push_back(ci->getOperand(1));
1356 new CallInst(fwrite_func,args,ci->getName(),ci);
1357 ci->replaceAllUsesWith(ConstantSInt::get(Type::IntTy,len));
1362 ConstantInt* CI = dyn_cast<ConstantInt>(ci->getOperand(3));
1366 const Type* FILEptr_type = ci->getOperand(1)->getType();
1367 Function* fputc_func = SLC.get_fputc(FILEptr_type);
1370 CastInst* cast = new CastInst(CI,Type::IntTy,CI->getName()+".int",ci);
1371 new CallInst(fputc_func,cast,ci->getOperand(1),"",ci);
1372 ci->replaceAllUsesWith(ConstantSInt::get(Type::IntTy,1));
1378 ci->eraseFromParent();
1383 /// This LibCallOptimization will simplify calls to the "sprintf" library
1384 /// function. It looks for cases where the result of sprintf is not used and the
1385 /// operation can be reduced to something simpler.
1386 /// @brief Simplify the pow library function.
1387 struct SPrintFOptimization : public LibCallOptimization {
1389 /// @brief Default Constructor
1390 SPrintFOptimization() : LibCallOptimization("sprintf",
1391 "Number of 'sprintf' calls simplified") {}
1393 /// @brief Make sure that the "fprintf" function has the right prototype
1394 virtual bool ValidateCalledFunction(const Function *f, SimplifyLibCalls &SLC){
1395 // Just make sure this has at least 2 arguments
1396 return (f->getReturnType() == Type::IntTy && f->arg_size() >= 2);
1399 /// @brief Perform the sprintf optimization.
1400 virtual bool OptimizeCall(CallInst *ci, SimplifyLibCalls &SLC) {
1401 // If the call has more than 3 operands, we can't optimize it
1402 if (ci->getNumOperands() > 4 || ci->getNumOperands() < 3)
1405 // All the optimizations depend on the length of the second argument and the
1406 // fact that it is a constant string array. Check that now
1408 ConstantArray* CA = 0;
1409 if (!getConstantStringLength(ci->getOperand(2), len, &CA))
1412 if (ci->getNumOperands() == 3) {
1414 // If the length is 0, we just need to store a null byte
1415 new StoreInst(ConstantInt::get(Type::SByteTy,0),ci->getOperand(1),ci);
1416 ci->replaceAllUsesWith(ConstantSInt::get(Type::IntTy,0));
1417 ci->eraseFromParent();
1421 // Make sure there's no % in the constant array
1422 for (unsigned i = 0; i < len; ++i) {
1423 if (ConstantInt* CI = dyn_cast<ConstantInt>(CA->getOperand(i))) {
1424 // Check for the null terminator
1425 if (CI->getRawValue() == '%')
1426 return false; // we found a %, can't optimize
1428 return false; // initializer is not constant int, can't optimize
1432 // Increment length because we want to copy the null byte too
1435 // sprintf(str,fmt) -> llvm.memcpy(str,fmt,strlen(fmt),1)
1436 Function* memcpy_func = SLC.get_memcpy();
1439 std::vector<Value*> args;
1440 args.push_back(ci->getOperand(1));
1441 args.push_back(ci->getOperand(2));
1442 args.push_back(ConstantUInt::get(SLC.getIntPtrType(),len));
1443 args.push_back(ConstantUInt::get(Type::UIntTy,1));
1444 new CallInst(memcpy_func,args,"",ci);
1445 ci->replaceAllUsesWith(ConstantSInt::get(Type::IntTy,len));
1446 ci->eraseFromParent();
1450 // The remaining optimizations require the format string to be length 2
1455 // The first character has to be a %
1456 if (ConstantInt* CI = dyn_cast<ConstantInt>(CA->getOperand(0)))
1457 if (CI->getRawValue() != '%')
1460 // Get the second character and switch on its value
1461 ConstantInt* CI = dyn_cast<ConstantInt>(CA->getOperand(1));
1462 switch (CI->getRawValue()) {
1464 // sprintf(dest,"%s",str) -> llvm.memcpy(dest, str, strlen(str)+1, 1)
1465 Function* strlen_func = SLC.get_strlen();
1466 Function* memcpy_func = SLC.get_memcpy();
1467 if (!strlen_func || !memcpy_func)
1470 Value *Len = new CallInst(strlen_func, CastToCStr(ci->getOperand(3), *ci),
1471 ci->getOperand(3)->getName()+".len", ci);
1472 Value *Len1 = BinaryOperator::createAdd(Len,
1473 ConstantInt::get(Len->getType(), 1),
1474 Len->getName()+"1", ci);
1475 if (Len1->getType() != SLC.getIntPtrType())
1476 Len1 = new CastInst(Len1, SLC.getIntPtrType(), Len1->getName(), ci);
1477 std::vector<Value*> args;
1478 args.push_back(CastToCStr(ci->getOperand(1), *ci));
1479 args.push_back(CastToCStr(ci->getOperand(3), *ci));
1480 args.push_back(Len1);
1481 args.push_back(ConstantUInt::get(Type::UIntTy,1));
1482 new CallInst(memcpy_func, args, "", ci);
1484 // The strlen result is the unincremented number of bytes in the string.
1485 if (!ci->use_empty()) {
1486 if (Len->getType() != ci->getType())
1487 Len = new CastInst(Len, ci->getType(), Len->getName(), ci);
1488 ci->replaceAllUsesWith(Len);
1490 ci->eraseFromParent();
1494 // sprintf(dest,"%c",chr) -> store chr, dest
1495 CastInst* cast = new CastInst(ci->getOperand(3),Type::SByteTy,"char",ci);
1496 new StoreInst(cast, ci->getOperand(1), ci);
1497 GetElementPtrInst* gep = new GetElementPtrInst(ci->getOperand(1),
1498 ConstantUInt::get(Type::UIntTy,1),ci->getOperand(1)->getName()+".end",
1500 new StoreInst(ConstantInt::get(Type::SByteTy,0),gep,ci);
1501 ci->replaceAllUsesWith(ConstantSInt::get(Type::IntTy,1));
1502 ci->eraseFromParent();
1510 /// This LibCallOptimization will simplify calls to the "fputs" library
1511 /// function. It looks for cases where the result of fputs is not used and the
1512 /// operation can be reduced to something simpler.
1513 /// @brief Simplify the pow library function.
1514 struct PutsOptimization : public LibCallOptimization {
1516 /// @brief Default Constructor
1517 PutsOptimization() : LibCallOptimization("fputs",
1518 "Number of 'fputs' calls simplified") {}
1520 /// @brief Make sure that the "fputs" function has the right prototype
1521 virtual bool ValidateCalledFunction(const Function *F, SimplifyLibCalls &SLC){
1522 // Just make sure this has 2 arguments
1523 return F->arg_size() == 2;
1526 /// @brief Perform the fputs optimization.
1527 virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& SLC) {
1528 // If the result is used, none of these optimizations work
1529 if (!ci->use_empty())
1532 // All the optimizations depend on the length of the first argument and the
1533 // fact that it is a constant string array. Check that now
1535 if (!getConstantStringLength(ci->getOperand(1), len))
1540 // fputs("",F) -> noop
1544 // fputs(s,F) -> fputc(s[0],F) (if s is constant and strlen(s) == 1)
1545 const Type* FILEptr_type = ci->getOperand(2)->getType();
1546 Function* fputc_func = SLC.get_fputc(FILEptr_type);
1549 LoadInst* loadi = new LoadInst(ci->getOperand(1),
1550 ci->getOperand(1)->getName()+".byte",ci);
1551 CastInst* casti = new CastInst(loadi,Type::IntTy,
1552 loadi->getName()+".int",ci);
1553 new CallInst(fputc_func,casti,ci->getOperand(2),"",ci);
1558 // fputs(s,F) -> fwrite(s,1,len,F) (if s is constant and strlen(s) > 1)
1559 const Type* FILEptr_type = ci->getOperand(2)->getType();
1560 Function* fwrite_func = SLC.get_fwrite(FILEptr_type);
1563 std::vector<Value*> parms;
1564 parms.push_back(ci->getOperand(1));
1565 parms.push_back(ConstantUInt::get(SLC.getIntPtrType(),len));
1566 parms.push_back(ConstantUInt::get(SLC.getIntPtrType(),1));
1567 parms.push_back(ci->getOperand(2));
1568 new CallInst(fwrite_func,parms,"",ci);
1572 ci->eraseFromParent();
1573 return true; // success
1577 /// This LibCallOptimization will simplify calls to the "isdigit" library
1578 /// function. It simply does range checks the parameter explicitly.
1579 /// @brief Simplify the isdigit library function.
1580 struct isdigitOptimization : public LibCallOptimization {
1582 isdigitOptimization() : LibCallOptimization("isdigit",
1583 "Number of 'isdigit' calls simplified") {}
1585 /// @brief Make sure that the "isdigit" function has the right prototype
1586 virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC){
1587 // Just make sure this has 1 argument
1588 return (f->arg_size() == 1);
1591 /// @brief Perform the toascii optimization.
1592 virtual bool OptimizeCall(CallInst *ci, SimplifyLibCalls &SLC) {
1593 if (ConstantInt* CI = dyn_cast<ConstantInt>(ci->getOperand(1))) {
1594 // isdigit(c) -> 0 or 1, if 'c' is constant
1595 uint64_t val = CI->getRawValue();
1596 if (val >= '0' && val <='9')
1597 ci->replaceAllUsesWith(ConstantSInt::get(Type::IntTy,1));
1599 ci->replaceAllUsesWith(ConstantSInt::get(Type::IntTy,0));
1600 ci->eraseFromParent();
1604 // isdigit(c) -> (unsigned)c - '0' <= 9
1606 new CastInst(ci->getOperand(1),Type::UIntTy,
1607 ci->getOperand(1)->getName()+".uint",ci);
1608 BinaryOperator* sub_inst = BinaryOperator::createSub(cast,
1609 ConstantUInt::get(Type::UIntTy,0x30),
1610 ci->getOperand(1)->getName()+".sub",ci);
1611 SetCondInst* setcond_inst = new SetCondInst(Instruction::SetLE,sub_inst,
1612 ConstantUInt::get(Type::UIntTy,9),
1613 ci->getOperand(1)->getName()+".cmp",ci);
1615 new CastInst(setcond_inst,Type::IntTy,
1616 ci->getOperand(1)->getName()+".isdigit",ci);
1617 ci->replaceAllUsesWith(c2);
1618 ci->eraseFromParent();
1623 struct isasciiOptimization : public LibCallOptimization {
1625 isasciiOptimization()
1626 : LibCallOptimization("isascii", "Number of 'isascii' calls simplified") {}
1628 virtual bool ValidateCalledFunction(const Function *F, SimplifyLibCalls &SLC){
1629 return F->arg_size() == 1 && F->arg_begin()->getType()->isInteger() &&
1630 F->getReturnType()->isInteger();
1633 /// @brief Perform the isascii optimization.
1634 virtual bool OptimizeCall(CallInst *CI, SimplifyLibCalls &SLC) {
1635 // isascii(c) -> (unsigned)c < 128
1636 Value *V = CI->getOperand(1);
1637 if (V->getType()->isSigned())
1638 V = new CastInst(V, V->getType()->getUnsignedVersion(), V->getName(), CI);
1639 Value *Cmp = BinaryOperator::createSetLT(V, ConstantUInt::get(V->getType(),
1641 V->getName()+".isascii", CI);
1642 if (Cmp->getType() != CI->getType())
1643 Cmp = new CastInst(Cmp, CI->getType(), Cmp->getName(), CI);
1644 CI->replaceAllUsesWith(Cmp);
1645 CI->eraseFromParent();
1651 /// This LibCallOptimization will simplify calls to the "toascii" library
1652 /// function. It simply does the corresponding and operation to restrict the
1653 /// range of values to the ASCII character set (0-127).
1654 /// @brief Simplify the toascii library function.
1655 struct ToAsciiOptimization : public LibCallOptimization {
1657 /// @brief Default Constructor
1658 ToAsciiOptimization() : LibCallOptimization("toascii",
1659 "Number of 'toascii' calls simplified") {}
1661 /// @brief Make sure that the "fputs" function has the right prototype
1662 virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC){
1663 // Just make sure this has 2 arguments
1664 return (f->arg_size() == 1);
1667 /// @brief Perform the toascii optimization.
1668 virtual bool OptimizeCall(CallInst *ci, SimplifyLibCalls &SLC) {
1669 // toascii(c) -> (c & 0x7f)
1670 Value* chr = ci->getOperand(1);
1671 BinaryOperator* and_inst = BinaryOperator::createAnd(chr,
1672 ConstantInt::get(chr->getType(),0x7F),ci->getName()+".toascii",ci);
1673 ci->replaceAllUsesWith(and_inst);
1674 ci->eraseFromParent();
1679 /// This LibCallOptimization will simplify calls to the "ffs" library
1680 /// calls which find the first set bit in an int, long, or long long. The
1681 /// optimization is to compute the result at compile time if the argument is
1683 /// @brief Simplify the ffs library function.
1684 struct FFSOptimization : public LibCallOptimization {
1686 /// @brief Subclass Constructor
1687 FFSOptimization(const char* funcName, const char* description)
1688 : LibCallOptimization(funcName, description) {}
1691 /// @brief Default Constructor
1692 FFSOptimization() : LibCallOptimization("ffs",
1693 "Number of 'ffs' calls simplified") {}
1695 /// @brief Make sure that the "ffs" function has the right prototype
1696 virtual bool ValidateCalledFunction(const Function *F, SimplifyLibCalls &SLC){
1697 // Just make sure this has 2 arguments
1698 return F->arg_size() == 1 && F->getReturnType() == Type::IntTy;
1701 /// @brief Perform the ffs optimization.
1702 virtual bool OptimizeCall(CallInst *TheCall, SimplifyLibCalls &SLC) {
1703 if (ConstantInt *CI = dyn_cast<ConstantInt>(TheCall->getOperand(1))) {
1704 // ffs(cnst) -> bit#
1705 // ffsl(cnst) -> bit#
1706 // ffsll(cnst) -> bit#
1707 uint64_t val = CI->getRawValue();
1711 while ((val & 1) == 0) {
1716 TheCall->replaceAllUsesWith(ConstantSInt::get(Type::IntTy, result));
1717 TheCall->eraseFromParent();
1721 // ffs(x) -> x == 0 ? 0 : llvm.cttz(x)+1
1722 // ffsl(x) -> x == 0 ? 0 : llvm.cttz(x)+1
1723 // ffsll(x) -> x == 0 ? 0 : llvm.cttz(x)+1
1724 const Type *ArgType = TheCall->getOperand(1)->getType();
1725 ArgType = ArgType->getUnsignedVersion();
1726 const char *CTTZName;
1727 switch (ArgType->getTypeID()) {
1728 default: assert(0 && "Unknown unsigned type!");
1729 case Type::UByteTyID : CTTZName = "llvm.cttz.i8" ; break;
1730 case Type::UShortTyID: CTTZName = "llvm.cttz.i16"; break;
1731 case Type::UIntTyID : CTTZName = "llvm.cttz.i32"; break;
1732 case Type::ULongTyID : CTTZName = "llvm.cttz.i64"; break;
1735 Function *F = SLC.getModule()->getOrInsertFunction(CTTZName, ArgType,
1737 Value *V = new CastInst(TheCall->getOperand(1), ArgType, "tmp", TheCall);
1738 Value *V2 = new CallInst(F, V, "tmp", TheCall);
1739 V2 = new CastInst(V2, Type::IntTy, "tmp", TheCall);
1740 V2 = BinaryOperator::createAdd(V2, ConstantSInt::get(Type::IntTy, 1),
1743 BinaryOperator::createSetEQ(V, Constant::getNullValue(V->getType()),
1745 V2 = new SelectInst(Cond, ConstantInt::get(Type::IntTy, 0), V2,
1746 TheCall->getName(), TheCall);
1747 TheCall->replaceAllUsesWith(V2);
1748 TheCall->eraseFromParent();
1753 /// This LibCallOptimization will simplify calls to the "ffsl" library
1754 /// calls. It simply uses FFSOptimization for which the transformation is
1756 /// @brief Simplify the ffsl library function.
1757 struct FFSLOptimization : public FFSOptimization {
1759 /// @brief Default Constructor
1760 FFSLOptimization() : FFSOptimization("ffsl",
1761 "Number of 'ffsl' calls simplified") {}
1765 /// This LibCallOptimization will simplify calls to the "ffsll" library
1766 /// calls. It simply uses FFSOptimization for which the transformation is
1768 /// @brief Simplify the ffsl library function.
1769 struct FFSLLOptimization : public FFSOptimization {
1771 /// @brief Default Constructor
1772 FFSLLOptimization() : FFSOptimization("ffsll",
1773 "Number of 'ffsll' calls simplified") {}
1777 /// This optimizes unary functions that take and return doubles.
1778 struct UnaryDoubleFPOptimizer : public LibCallOptimization {
1779 UnaryDoubleFPOptimizer(const char *Fn, const char *Desc)
1780 : LibCallOptimization(Fn, Desc) {}
1782 // Make sure that this function has the right prototype
1783 virtual bool ValidateCalledFunction(const Function *F, SimplifyLibCalls &SLC){
1784 return F->arg_size() == 1 && F->arg_begin()->getType() == Type::DoubleTy &&
1785 F->getReturnType() == Type::DoubleTy;
1788 /// ShrinkFunctionToFloatVersion - If the input to this function is really a
1789 /// float, strength reduce this to a float version of the function,
1790 /// e.g. floor((double)FLT) -> (double)floorf(FLT). This can only be called
1791 /// when the target supports the destination function and where there can be
1792 /// no precision loss.
1793 static bool ShrinkFunctionToFloatVersion(CallInst *CI, SimplifyLibCalls &SLC,
1794 Function *(SimplifyLibCalls::*FP)()){
1795 if (CastInst *Cast = dyn_cast<CastInst>(CI->getOperand(1)))
1796 if (Cast->getOperand(0)->getType() == Type::FloatTy) {
1797 Value *New = new CallInst((SLC.*FP)(), Cast->getOperand(0),
1799 New = new CastInst(New, Type::DoubleTy, CI->getName(), CI);
1800 CI->replaceAllUsesWith(New);
1801 CI->eraseFromParent();
1802 if (Cast->use_empty())
1803 Cast->eraseFromParent();
1811 struct FloorOptimization : public UnaryDoubleFPOptimizer {
1813 : UnaryDoubleFPOptimizer("floor", "Number of 'floor' calls simplified") {}
1815 virtual bool OptimizeCall(CallInst *CI, SimplifyLibCalls &SLC) {
1817 // If this is a float argument passed in, convert to floorf.
1818 if (ShrinkFunctionToFloatVersion(CI, SLC, &SimplifyLibCalls::get_floorf))
1821 return false; // opt failed
1825 struct CeilOptimization : public UnaryDoubleFPOptimizer {
1827 : UnaryDoubleFPOptimizer("ceil", "Number of 'ceil' calls simplified") {}
1829 virtual bool OptimizeCall(CallInst *CI, SimplifyLibCalls &SLC) {
1831 // If this is a float argument passed in, convert to ceilf.
1832 if (ShrinkFunctionToFloatVersion(CI, SLC, &SimplifyLibCalls::get_ceilf))
1835 return false; // opt failed
1839 struct RoundOptimization : public UnaryDoubleFPOptimizer {
1841 : UnaryDoubleFPOptimizer("round", "Number of 'round' calls simplified") {}
1843 virtual bool OptimizeCall(CallInst *CI, SimplifyLibCalls &SLC) {
1845 // If this is a float argument passed in, convert to roundf.
1846 if (ShrinkFunctionToFloatVersion(CI, SLC, &SimplifyLibCalls::get_roundf))
1849 return false; // opt failed
1853 struct RintOptimization : public UnaryDoubleFPOptimizer {
1855 : UnaryDoubleFPOptimizer("rint", "Number of 'rint' calls simplified") {}
1857 virtual bool OptimizeCall(CallInst *CI, SimplifyLibCalls &SLC) {
1859 // If this is a float argument passed in, convert to rintf.
1860 if (ShrinkFunctionToFloatVersion(CI, SLC, &SimplifyLibCalls::get_rintf))
1863 return false; // opt failed
1867 struct NearByIntOptimization : public UnaryDoubleFPOptimizer {
1868 NearByIntOptimization()
1869 : UnaryDoubleFPOptimizer("nearbyint",
1870 "Number of 'nearbyint' calls simplified") {}
1872 virtual bool OptimizeCall(CallInst *CI, SimplifyLibCalls &SLC) {
1873 #ifdef HAVE_NEARBYINTF
1874 // If this is a float argument passed in, convert to nearbyintf.
1875 if (ShrinkFunctionToFloatVersion(CI, SLC,&SimplifyLibCalls::get_nearbyintf))
1878 return false; // opt failed
1880 } NearByIntOptimizer;
1882 /// A function to compute the length of a null-terminated constant array of
1883 /// integers. This function can't rely on the size of the constant array
1884 /// because there could be a null terminator in the middle of the array.
1885 /// We also have to bail out if we find a non-integer constant initializer
1886 /// of one of the elements or if there is no null-terminator. The logic
1887 /// below checks each of these conditions and will return true only if all
1888 /// conditions are met. In that case, the \p len parameter is set to the length
1889 /// of the null-terminated string. If false is returned, the conditions were
1890 /// not met and len is set to 0.
1891 /// @brief Get the length of a constant string (null-terminated array).
1892 bool getConstantStringLength(Value *V, uint64_t &len, ConstantArray **CA) {
1893 assert(V != 0 && "Invalid args to getConstantStringLength");
1894 len = 0; // make sure we initialize this
1896 // If the value is not a GEP instruction nor a constant expression with a
1897 // GEP instruction, then return false because ConstantArray can't occur
1899 if (GetElementPtrInst* GEPI = dyn_cast<GetElementPtrInst>(V))
1901 else if (ConstantExpr* CE = dyn_cast<ConstantExpr>(V))
1902 if (CE->getOpcode() == Instruction::GetElementPtr)
1909 // Make sure the GEP has exactly three arguments.
1910 if (GEP->getNumOperands() != 3)
1913 // Check to make sure that the first operand of the GEP is an integer and
1914 // has value 0 so that we are sure we're indexing into the initializer.
1915 if (ConstantInt* op1 = dyn_cast<ConstantInt>(GEP->getOperand(1))) {
1916 if (!op1->isNullValue())
1921 // Ensure that the second operand is a ConstantInt. If it isn't then this
1922 // GEP is wonky and we're not really sure what were referencing into and
1923 // better of not optimizing it. While we're at it, get the second index
1924 // value. We'll need this later for indexing the ConstantArray.
1925 uint64_t start_idx = 0;
1926 if (ConstantInt* CI = dyn_cast<ConstantInt>(GEP->getOperand(2)))
1927 start_idx = CI->getRawValue();
1931 // The GEP instruction, constant or instruction, must reference a global
1932 // variable that is a constant and is initialized. The referenced constant
1933 // initializer is the array that we'll use for optimization.
1934 GlobalVariable* GV = dyn_cast<GlobalVariable>(GEP->getOperand(0));
1935 if (!GV || !GV->isConstant() || !GV->hasInitializer())
1938 // Get the initializer.
1939 Constant* INTLZR = GV->getInitializer();
1941 // Handle the ConstantAggregateZero case
1942 if (ConstantAggregateZero *CAZ = dyn_cast<ConstantAggregateZero>(INTLZR)) {
1943 // This is a degenerate case. The initializer is constant zero so the
1944 // length of the string must be zero.
1949 // Must be a Constant Array
1950 ConstantArray* A = dyn_cast<ConstantArray>(INTLZR);
1954 // Get the number of elements in the array
1955 uint64_t max_elems = A->getType()->getNumElements();
1957 // Traverse the constant array from start_idx (derived above) which is
1958 // the place the GEP refers to in the array.
1959 for (len = start_idx; len < max_elems; len++) {
1960 if (ConstantInt *CI = dyn_cast<ConstantInt>(A->getOperand(len))) {
1961 // Check for the null terminator
1962 if (CI->isNullValue())
1963 break; // we found end of string
1965 return false; // This array isn't suitable, non-int initializer
1968 if (len >= max_elems)
1969 return false; // This array isn't null terminated
1971 // Subtract out the initial value from the length
1975 return true; // success!
1978 /// CastToCStr - Return V if it is an sbyte*, otherwise cast it to sbyte*,
1979 /// inserting the cast before IP, and return the cast.
1980 /// @brief Cast a value to a "C" string.
1981 Value *CastToCStr(Value *V, Instruction &IP) {
1982 const Type *SBPTy = PointerType::get(Type::SByteTy);
1983 if (V->getType() != SBPTy)
1984 return new CastInst(V, SBPTy, V->getName(), &IP);
1989 // Additional cases that we need to add to this file:
1992 // * cbrt(expN(X)) -> expN(x/3)
1993 // * cbrt(sqrt(x)) -> pow(x,1/6)
1994 // * cbrt(sqrt(x)) -> pow(x,1/9)
1997 // * cos(-x) -> cos(x)
2000 // * exp(log(x)) -> x
2003 // * log(exp(x)) -> x
2004 // * log(x**y) -> y*log(x)
2005 // * log(exp(y)) -> y*log(e)
2006 // * log(exp2(y)) -> y*log(2)
2007 // * log(exp10(y)) -> y*log(10)
2008 // * log(sqrt(x)) -> 0.5*log(x)
2009 // * log(pow(x,y)) -> y*log(x)
2011 // lround, lroundf, lroundl:
2012 // * lround(cnst) -> cnst'
2015 // * memcmp(x,y,l) -> cnst
2016 // (if all arguments are constant and strlen(x) <= l and strlen(y) <= l)
2019 // * memmove(d,s,l,a) -> memcpy(d,s,l,a)
2020 // (if s is a global constant array)
2023 // * pow(exp(x),y) -> exp(x*y)
2024 // * pow(sqrt(x),y) -> pow(x,y*0.5)
2025 // * pow(pow(x,y),z)-> pow(x,y*z)
2028 // * puts("") -> fputc("\n",stdout) (how do we get "stdout"?)
2030 // round, roundf, roundl:
2031 // * round(cnst) -> cnst'
2034 // * signbit(cnst) -> cnst'
2035 // * signbit(nncst) -> 0 (if pstv is a non-negative constant)
2037 // sqrt, sqrtf, sqrtl:
2038 // * sqrt(expN(x)) -> expN(x*0.5)
2039 // * sqrt(Nroot(x)) -> pow(x,1/(2*N))
2040 // * sqrt(pow(x,y)) -> pow(|x|,y*0.5)
2043 // * stpcpy(str, "literal") ->
2044 // llvm.memcpy(str,"literal",strlen("literal")+1,1)
2046 // * strrchr(s,c) -> reverse_offset_of_in(c,s)
2047 // (if c is a constant integer and s is a constant string)
2048 // * strrchr(s1,0) -> strchr(s1,0)
2051 // * strncat(x,y,0) -> x
2052 // * strncat(x,y,0) -> x (if strlen(y) = 0)
2053 // * strncat(x,y,l) -> strcat(x,y) (if y and l are constants an l > strlen(y))
2056 // * strncpy(d,s,0) -> d
2057 // * strncpy(d,s,l) -> memcpy(d,s,l,1)
2058 // (if s and l are constants)
2061 // * strpbrk(s,a) -> offset_in_for(s,a)
2062 // (if s and a are both constant strings)
2063 // * strpbrk(s,"") -> 0
2064 // * strpbrk(s,a) -> strchr(s,a[0]) (if a is constant string of length 1)
2067 // * strspn(s,a) -> const_int (if both args are constant)
2068 // * strspn("",a) -> 0
2069 // * strspn(s,"") -> 0
2070 // * strcspn(s,a) -> const_int (if both args are constant)
2071 // * strcspn("",a) -> 0
2072 // * strcspn(s,"") -> strlen(a)
2075 // * strstr(x,x) -> x
2076 // * strstr(s1,s2) -> offset_of_s2_in(s1)
2077 // (if s1 and s2 are constant strings)
2080 // * tan(atan(x)) -> x
2082 // trunc, truncf, truncl:
2083 // * trunc(cnst) -> cnst'