1 //===- PreSelection.cpp - Specialize LLVM code for target machine ---------===//
3 // This file defines the PreSelection pass which specializes LLVM code for a
4 // target machine, while remaining in legal portable LLVM form and
5 // preserving type information and type safety. This is meant to enable
6 // dataflow optimizations on target-specific operations such as accesses to
7 // constants, globals, and array indexing.
9 //===----------------------------------------------------------------------===//
11 #include "llvm/CodeGen/PreSelection.h"
12 #include "llvm/Target/TargetMachine.h"
13 #include "llvm/Target/TargetInstrInfo.h"
14 #include "llvm/Transforms/Scalar.h"
15 #include "llvm/Support/InstVisitor.h"
16 #include "llvm/Module.h"
17 #include "llvm/Constants.h"
18 #include "llvm/iMemory.h"
19 #include "llvm/iPHINode.h"
20 #include "llvm/iOther.h"
21 #include "llvm/DerivedTypes.h"
22 #include "llvm/Pass.h"
23 #include "Support/CommandLine.h"
27 //===--------------------------------------------------------------------===//
28 // SelectDebugLevel - Allow command line control over debugging.
30 enum PreSelectDebugLevel_t {
31 PreSelect_NoDebugInfo,
32 PreSelect_PrintOutput,
35 // Enable Debug Options to be specified on the command line
36 cl::opt<PreSelectDebugLevel_t>
37 PreSelectDebugLevel("dpreselect", cl::Hidden,
38 cl::desc("debug information for target-dependent pre-selection"),
40 clEnumValN(PreSelect_NoDebugInfo, "n", "disable debug output (default)"),
41 clEnumValN(PreSelect_PrintOutput, "y", "print generated machine code"),
42 /* default level = */ PreSelect_NoDebugInfo));
45 //===--------------------------------------------------------------------===//
46 // class ConstantPoolForModule:
48 // The pool of constants that must be emitted for a module.
49 // This is a single pool for the entire module and is shared by
50 // all invocations of the PreSelection pass for this module by putting
51 // this as an annotation on the Module object.
52 // A single GlobalVariable is created for each constant in the pool
53 // representing the memory for that constant.
55 AnnotationID CPFM_AID(
56 AnnotationManager::getID("CodeGen::ConstantPoolForModule"));
58 class ConstantPoolForModule : private Annotation {
60 std::map<const Constant*, GlobalVariable*> gvars;
61 std::map<const Constant*, GlobalVariable*> origGVars;
62 ConstantPoolForModule(Module* M); // called only by annotation builder
63 ConstantPoolForModule(); // DO NOT IMPLEMENT
64 void operator=(const ConstantPoolForModule&); // DO NOT IMPLEMENT
66 static ConstantPoolForModule& get(Module* M) {
67 ConstantPoolForModule* cpool =
68 (ConstantPoolForModule*) M->getAnnotation(CPFM_AID);
69 if (cpool == NULL) // create a new annotation and add it to the Module
70 M->addAnnotation(cpool = new ConstantPoolForModule(M));
74 GlobalVariable* getGlobalForConstant(Constant* CV) {
75 std::map<const Constant*, GlobalVariable*>::iterator I = gvars.find(CV);
77 return I->second; // global exists so return it
78 return addToConstantPool(CV); // create a new global and return it
81 GlobalVariable* addToConstantPool(Constant* CV) {
82 GlobalVariable*& GV = gvars[CV]; // handle to global var entry in map
84 { // check if a global constant already existed; otherwise create one
85 std::map<const Constant*, GlobalVariable*>::iterator PI =
87 if (PI != origGVars.end())
88 GV = PI->second; // put in map
91 GV = new GlobalVariable(CV->getType(), true, //put in map
92 GlobalValue::InternalLinkage, CV);
93 myModule->getGlobalList().push_back(GV); // GV owned by module now
101 ConstantPoolForModule::ConstantPoolForModule(Module* M)
102 : Annotation(CPFM_AID), myModule(M)
104 // Build reverse map for pre-existing global constants so we can find them
105 for (Module::giterator GI = M->gbegin(), GE = M->gend(); GI != GE; ++GI)
106 if (GI->hasInitializer() && GI->isConstant())
107 origGVars[GI->getInitializer()] = GI;
110 //===--------------------------------------------------------------------===//
111 // PreSelection Pass - Specialize LLVM code for the current target machine.
112 // This was and will be a basicblock pass, but make it a FunctionPass until
113 // BasicBlockPass ::doFinalization(Function&) is available.
115 class PreSelection : public BasicBlockPass, public InstVisitor<PreSelection>
117 const TargetMachine ⌖
120 GlobalVariable* getGlobalForConstant(Constant* CV) {
121 Module* M = function->getParent();
122 return ConstantPoolForModule::get(M).getGlobalForConstant(CV);
126 PreSelection (const TargetMachine &T): target(T), function(NULL) {}
128 // runOnBasicBlock - apply this pass to each BB
129 bool runOnBasicBlock(BasicBlock &BB) {
130 function = BB.getParent();
135 bool doFinalization(Function &F) {
136 if (PreSelectDebugLevel >= PreSelect_PrintOutput)
137 std::cerr << "\n\n*** LLVM code after pre-selection for function "
138 << F.getName() << ":\n\n" << F;
142 // These methods do the actual work of specializing code
143 void visitInstruction(Instruction &I); // common work for every instr.
144 void visitGetElementPtrInst(GetElementPtrInst &I);
145 void visitLoadInst(LoadInst &I);
146 void visitCastInst(CastInst &I);
147 void visitStoreInst(StoreInst &I);
149 // Helper functions for visiting operands of every instruction
150 void visitOperands(Instruction &I); // work on all operands of instr.
151 void visitOneOperand(Instruction &I, Constant* CV, unsigned opNum,
152 Instruction& insertBefore); // iworks on one operand
155 // Register the pass...
156 RegisterOpt<PreSelection> X("preselect",
157 "Specialize LLVM code for a target machine",
158 createPreSelectionPass);
159 } // end anonymous namespace
162 //------------------------------------------------------------------------------
163 // Helper functions used by methods of class PreSelection
164 //------------------------------------------------------------------------------
167 // getGlobalAddr(): Put address of a global into a v. register.
168 static GetElementPtrInst* getGlobalAddr(Value* ptr, Instruction& insertBefore)
170 if (isa<ConstantPointerRef>(ptr))
171 ptr = cast<ConstantPointerRef>(ptr)->getValue();
173 return (isa<GlobalValue>(ptr))
174 ? new GetElementPtrInst(ptr,
175 std::vector<Value*>(1, ConstantSInt::get(Type::LongTy, 0U)),
176 "addrOfGlobal", &insertBefore)
181 // Wrapper on Constant::classof to use in find_if :-(
182 inline static bool nonConstant(const Use& U)
184 return ! isa<Constant>(U);
188 static Instruction* DecomposeConstantExpr(ConstantExpr* CE,
189 Instruction& insertBefore)
191 Value *getArg1, *getArg2;
193 switch(CE->getOpcode())
195 case Instruction::Cast:
196 getArg1 = CE->getOperand(0);
197 if (ConstantExpr* CEarg = dyn_cast<ConstantExpr>(getArg1))
198 getArg1 = DecomposeConstantExpr(CEarg, insertBefore);
199 return new CastInst(getArg1, CE->getType(), "constantCast",&insertBefore);
201 case Instruction::GetElementPtr:
202 assert(find_if(CE->op_begin()+1, CE->op_end(),nonConstant) == CE->op_end()
203 && "All indices in ConstantExpr getelementptr must be constant!");
204 getArg1 = CE->getOperand(0);
205 if (ConstantExpr* CEarg = dyn_cast<ConstantExpr>(getArg1))
206 getArg1 = DecomposeConstantExpr(CEarg, insertBefore);
207 else if (GetElementPtrInst* gep = getGlobalAddr(getArg1, insertBefore))
209 return new GetElementPtrInst(getArg1,
210 std::vector<Value*>(CE->op_begin()+1, CE->op_end()),
211 "constantGEP", &insertBefore);
213 default: // must be a binary operator
214 assert(CE->getOpcode() >= Instruction::BinaryOpsBegin &&
215 CE->getOpcode() < Instruction::BinaryOpsEnd &&
216 "Unrecognized opcode in ConstantExpr");
217 getArg1 = CE->getOperand(0);
218 if (ConstantExpr* CEarg = dyn_cast<ConstantExpr>(getArg1))
219 getArg1 = DecomposeConstantExpr(CEarg, insertBefore);
220 getArg2 = CE->getOperand(1);
221 if (ConstantExpr* CEarg = dyn_cast<ConstantExpr>(getArg2))
222 getArg2 = DecomposeConstantExpr(CEarg, insertBefore);
223 return BinaryOperator::create((Instruction::BinaryOps) CE->getOpcode(),
225 "constantBinaryOp", &insertBefore);
230 //------------------------------------------------------------------------------
231 // Instruction visitor methods to perform instruction-specific operations
232 //------------------------------------------------------------------------------
234 // Common work for *all* instructions. This needs to be called explicitly
235 // by other visit<InstructionType> functions.
237 PreSelection::visitInstruction(Instruction &I)
239 visitOperands(I); // Perform operand transformations
243 // GetElementPtr instructions: check if pointer is a global
245 PreSelection::visitGetElementPtrInst(GetElementPtrInst &I)
247 // Check for a global and put its address into a register before this instr
248 if (GetElementPtrInst* gep = getGlobalAddr(I.getPointerOperand(), I))
249 I.setOperand(I.getPointerOperandIndex(), gep); // replace pointer operand
251 // Decompose multidimensional array references
252 DecomposeArrayRef(&I);
254 // Perform other transformations common to all instructions
259 // Load instructions: check if pointer is a global
261 PreSelection::visitLoadInst(LoadInst &I)
263 // Check for a global and put its address into a register before this instr
264 if (GetElementPtrInst* gep = getGlobalAddr(I.getPointerOperand(), I))
265 I.setOperand(I.getPointerOperandIndex(), gep); // replace pointer operand
267 // Perform other transformations common to all instructions
272 // Store instructions: check if pointer is a global
274 PreSelection::visitStoreInst(StoreInst &I)
276 // Check for a global and put its address into a register before this instr
277 if (GetElementPtrInst* gep = getGlobalAddr(I.getPointerOperand(), I))
278 I.setOperand(I.getPointerOperandIndex(), gep); // replace pointer operand
280 // Perform other transformations common to all instructions
285 // Cast instructions:
286 // -- check if argument is a global
287 // -- make multi-step casts explicit:
288 // -- float/double to uint32_t:
289 // If target does not have a float-to-unsigned instruction, we
290 // need to convert to uint64_t and then to uint32_t, or we may
291 // overflow the signed int representation for legal uint32_t
292 // values. Expand this without checking target.
295 PreSelection::visitCastInst(CastInst &I)
297 CastInst* castI = NULL;
299 // Check for a global and put its address into a register before this instr
300 if (GetElementPtrInst* gep = getGlobalAddr(I.getOperand(0), I))
302 I.setOperand(0, gep); // replace pointer operand
304 else if (I.getType() == Type::UIntTy &&
305 I.getOperand(0)->getType()->isFloatingPoint())
306 { // insert a cast-fp-to-long before I, and then replace the operand of I
307 castI = new CastInst(I.getOperand(0), Type::LongTy, "fp2Long2Uint", &I);
308 I.setOperand(0, castI); // replace fp operand with long
311 // Perform other transformations common to all instructions
314 visitInstruction(*castI);
318 // visitOperands() transforms individual operands of all instructions:
319 // -- Load "large" int constants into a virtual register. What is large
320 // depends on the type of instruction and on the target architecture.
321 // -- For any constants that cannot be put in an immediate field,
322 // load address into virtual register first, and then load the constant.
325 PreSelection::visitOperands(Instruction &I)
327 // For any instruction other than PHI, copies go just before the instr.
328 // For a PHI, operand copies must be before the terminator of the
329 // appropriate predecessor basic block. Remaining logic is simple
330 // so just handle PHIs and other instructions separately.
332 if (PHINode* phi = dyn_cast<PHINode>(&I))
334 for (unsigned i=0, N=phi->getNumIncomingValues(); i < N; ++i)
335 if (Constant* CV = dyn_cast<Constant>(phi->getIncomingValue(i)))
336 this->visitOneOperand(I, CV, phi->getOperandNumForIncomingValue(i),
337 * phi->getIncomingBlock(i)->getTerminator());
340 for (unsigned i=0, N=I.getNumOperands(); i < N; ++i)
341 if (Constant* CV = dyn_cast<Constant>(I.getOperand(i)))
342 this->visitOneOperand(I, CV, i, I);
346 PreSelection::visitOneOperand(Instruction &I, Constant* CV, unsigned opNum,
347 Instruction& insertBefore)
349 if (ConstantExpr* CE = dyn_cast<ConstantExpr>(CV))
350 { // load-time constant: factor it out so we optimize as best we can
351 Instruction* computeConst = DecomposeConstantExpr(CE, insertBefore);
352 I.setOperand(opNum, computeConst); // replace expr operand with result
354 else if (target.getInstrInfo().ConstantTypeMustBeLoaded(CV))
355 { // load address of constant into a register, then load the constant
356 GetElementPtrInst* gep = getGlobalAddr(getGlobalForConstant(CV),
358 LoadInst* ldI = new LoadInst(gep, "loadConst", &insertBefore);
359 I.setOperand(opNum, ldI); // replace operand with copy in v.reg.
361 else if (target.getInstrInfo().ConstantMayNotFitInImmedField(CV, &I))
362 { // put the constant into a virtual register using a cast
363 CastInst* castI = new CastInst(CV, CV->getType(), "copyConst",
365 I.setOperand(opNum, castI); // replace operand with copy in v.reg.
370 //===----------------------------------------------------------------------===//
371 // createPreSelectionPass - Public entrypoint for pre-selection pass
372 // and this file as a whole...
375 createPreSelectionPass(TargetMachine &T)
377 return new PreSelection(T);