1 //===-- PartialSpecialization.cpp - Specialize for common constants--------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass finds function arguments that are often a common constant and
11 // specializes a version of the called function for that constant.
13 // This pass simply does the cloning for functions it specializes. It depends
14 // on IPSCCP and DAE to clean up the results.
16 // The initial heuristic favors constant arguments that are used in control
19 //===----------------------------------------------------------------------===//
21 #define DEBUG_TYPE "partialspecialization"
22 #include "llvm/Transforms/IPO.h"
23 #include "llvm/Constant.h"
24 #include "llvm/Instructions.h"
25 #include "llvm/Module.h"
26 #include "llvm/Pass.h"
27 #include "llvm/ADT/Statistic.h"
28 #include "llvm/Transforms/Utils/Cloning.h"
29 #include "llvm/Support/CallSite.h"
30 #include "llvm/Support/Compiler.h"
31 #include "llvm/ADT/DenseSet.h"
35 STATISTIC(numSpecialized, "Number of specialized functions created");
37 // Call must be used at least occasionally
38 static const int CallsMin = 5;
40 // Must have 10% of calls having the same constant to specialize on
41 static const double ConstValPercent = .1;
44 class VISIBILITY_HIDDEN PartSpec : public ModulePass {
45 void scanForInterest(Function&, SmallVector<int, 6>&);
46 int scanDistribution(Function&, int, std::map<Constant*, int>&);
48 static char ID; // Pass identification, replacement for typeid
49 PartSpec() : ModulePass(&ID) {}
50 bool runOnModule(Module &M);
54 char PartSpec::ID = 0;
55 static RegisterPass<PartSpec>
56 X("partialspecialization", "Partial Specialization");
58 // Specialize F by replacing the arguments (keys) in replacements with the
59 // constants (values). Replace all calls to F with those constants with
60 // a call to the specialized function. Returns the specialized function
62 SpecializeFunction(Function* F,
63 DenseMap<const Value*, Value*>& replacements) {
64 // arg numbers of deleted arguments
65 DenseSet<unsigned> deleted;
66 for (DenseMap<const Value*, Value*>::iterator
67 repb = replacements.begin(), repe = replacements.end();
69 deleted.insert(cast<Argument>(repb->first)->getArgNo());
71 Function* NF = CloneFunction(F, replacements);
72 NF->setLinkage(GlobalValue::InternalLinkage);
73 F->getParent()->getFunctionList().push_back(NF);
75 for (Value::use_iterator ii = F->use_begin(), ee = F->use_end();
77 Value::use_iterator i = ii;
79 if (isa<CallInst>(i) || isa<InvokeInst>(i)) {
80 CallSite CS(cast<Instruction>(i));
81 if (CS.getCalledFunction() == F) {
83 SmallVector<Value*, 6> args;
84 for (unsigned x = 0; x < CS.arg_size(); ++x)
85 if (!deleted.count(x))
86 args.push_back(CS.getArgument(x));
88 if (CallInst *CI = dyn_cast<CallInst>(i)) {
89 NCall = CallInst::Create(NF, args.begin(), args.end(),
91 cast<CallInst>(NCall)->setTailCall(CI->isTailCall());
92 cast<CallInst>(NCall)->setCallingConv(CI->getCallingConv());
94 InvokeInst *II = cast<InvokeInst>(i);
95 NCall = InvokeInst::Create(NF, II->getNormalDest(),
97 args.begin(), args.end(),
99 cast<InvokeInst>(NCall)->setCallingConv(II->getCallingConv());
101 CS.getInstruction()->replaceAllUsesWith(NCall);
102 CS.getInstruction()->eraseFromParent();
110 bool PartSpec::runOnModule(Module &M) {
111 Context = &M.getContext();
113 bool Changed = false;
114 for (Module::iterator I = M.begin(); I != M.end(); ++I) {
116 if (F.isDeclaration() || F.mayBeOverridden()) continue;
117 SmallVector<int, 6> interestingArgs;
118 scanForInterest(F, interestingArgs);
120 // Find the first interesting Argument that we can specialize on
121 // If there are multiple interesting Arguments, then those will be found
122 // when processing the cloned function.
123 bool breakOuter = false;
124 for (unsigned int x = 0; !breakOuter && x < interestingArgs.size(); ++x) {
125 std::map<Constant*, int> distribution;
126 int total = scanDistribution(F, interestingArgs[x], distribution);
127 if (total > CallsMin)
128 for (std::map<Constant*, int>::iterator ii = distribution.begin(),
129 ee = distribution.end(); ii != ee; ++ii)
130 if (total > ii->second && ii->first &&
131 ii->second > total * ConstValPercent) {
132 DenseMap<const Value*, Value*> m;
133 Function::arg_iterator arg = F.arg_begin();
134 for (int y = 0; y < interestingArgs[x]; ++y)
136 m[&*arg] = ii->first;
137 SpecializeFunction(&F, m);
147 /// scanForInterest - This function decides which arguments would be worth
149 void PartSpec::scanForInterest(Function& F, SmallVector<int, 6>& args) {
150 for(Function::arg_iterator ii = F.arg_begin(), ee = F.arg_end();
152 for(Value::use_iterator ui = ii->use_begin(), ue = ii->use_end();
155 bool interesting = false;
157 if (isa<CmpInst>(ui)) interesting = true;
158 else if (isa<CallInst>(ui))
159 interesting = ui->getOperand(0) == ii;
160 else if (isa<InvokeInst>(ui))
161 interesting = ui->getOperand(0) == ii;
162 else if (isa<SwitchInst>(ui)) interesting = true;
163 else if (isa<BranchInst>(ui)) interesting = true;
166 args.push_back(std::distance(F.arg_begin(), ii));
173 /// scanDistribution - Construct a histogram of constants for arg of F at arg.
174 int PartSpec::scanDistribution(Function& F, int arg,
175 std::map<Constant*, int>& dist) {
176 bool hasIndirect = false;
178 for(Value::use_iterator ii = F.use_begin(), ee = F.use_end();
180 if ((isa<CallInst>(ii) || isa<InvokeInst>(ii))
181 && ii->getOperand(0) == &F) {
182 ++dist[dyn_cast<Constant>(ii->getOperand(arg + 1))];
187 // Preserve the original address taken function even if all other uses
188 // will be specialized.
189 if (hasIndirect) ++total;
193 ModulePass* llvm::createPartialSpecializationPass() { return new PartSpec(); }