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();
68 repb != repe; ++ repb)
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));
89 NCall = CallInst::Create(NF, args.begin(), args.end(),
90 CS.getInstruction()->getName(),
93 NCall = InvokeInst::Create(NF, cast<InvokeInst>(i)->getNormalDest(),
94 cast<InvokeInst>(i)->getUnwindDest(),
95 args.begin(), args.end(),
96 CS.getInstruction()->getName(),
98 CS.getInstruction()->replaceAllUsesWith(NCall);
99 CS.getInstruction()->eraseFromParent();
107 bool PartSpec::runOnModule(Module &M) {
108 bool Changed = false;
109 for (Module::iterator I = M.begin(); I != M.end(); ++I) {
111 if (F.isDeclaration() || F.mayBeOverridden()) continue;
112 SmallVector<int, 6> interestingArgs;
113 scanForInterest(F, interestingArgs);
115 // Find the first interesting Argument that we can specialize on
116 // If there are multiple interesting Arguments, then those will be found
117 // when processing the cloned function.
118 bool breakOuter = false;
119 for (unsigned int x = 0; !breakOuter && x < interestingArgs.size(); ++x) {
120 std::map<Constant*, int> distribution;
121 int total = scanDistribution(F, interestingArgs[x], distribution);
122 if (total > CallsMin)
123 for (std::map<Constant*, int>::iterator ii = distribution.begin(),
124 ee = distribution.end(); ii != ee; ++ii)
125 if (total > ii->second && ii->first &&
126 ii->second > total * ConstValPercent) {
127 DenseMap<const Value*, Value*> m;
128 Function::arg_iterator arg = F.arg_begin();
129 for (int y = 0; y < interestingArgs[x]; ++y)
131 m[&*arg] = ii->first;
132 SpecializeFunction(&F, m);
142 /// scanForInterest - This function decides which arguments would be worth
144 void PartSpec::scanForInterest(Function& F, SmallVector<int, 6>& args) {
145 for(Function::arg_iterator ii = F.arg_begin(), ee = F.arg_end();
147 for(Value::use_iterator ui = ii->use_begin(), ue = ii->use_end();
150 bool interesting = false;
152 if (isa<CmpInst>(ui)) interesting = true;
153 else if (isa<CallInst>(ui))
154 interesting = ui->getOperand(0) == ii;
155 else if (isa<InvokeInst>(ui))
156 interesting = ui->getOperand(0) == ii;
157 else if (isa<SwitchInst>(ui)) interesting = true;
158 else if (isa<BranchInst>(ui)) interesting = true;
161 args.push_back(std::distance(F.arg_begin(), ii));
168 /// scanDistribution - Construct a histogram of constants for arg of F at arg.
169 int PartSpec::scanDistribution(Function& F, int arg,
170 std::map<Constant*, int>& dist) {
171 bool hasIndirect = false;
173 for(Value::use_iterator ii = F.use_begin(), ee = F.use_end();
175 if ((isa<CallInst>(ii) || isa<InvokeInst>(ii))
176 && ii->getOperand(0) == &F) {
177 ++dist[dyn_cast<Constant>(ii->getOperand(arg + 1))];
182 // Preserve the original address taken function even if all other uses
183 // will be specialized.
184 if (hasIndirect) ++total;
188 ModulePass* llvm::createPartialSpecializationPass() { return new PartSpec(); }