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/ADT/DenseSet.h"
34 STATISTIC(numSpecialized, "Number of specialized functions created");
35 STATISTIC(numReplaced, "Number of callers replaced by specialization");
37 // Maximum number of arguments markable interested
38 static const int MaxInterests = 6;
40 // Call must be used at least occasionally
41 static const int CallsMin = 5;
43 // Must have 10% of calls having the same constant to specialize on
44 static const double ConstValPercent = .1;
47 typedef SmallVector<int, MaxInterests> InterestingArgVector;
48 class PartSpec : public ModulePass {
49 void scanForInterest(Function&, InterestingArgVector&);
50 int scanDistribution(Function&, int, std::map<Constant*, int>&);
52 static char ID; // Pass identification, replacement for typeid
53 PartSpec() : ModulePass(ID) {}
54 bool runOnModule(Module &M);
58 char PartSpec::ID = 0;
59 INITIALIZE_PASS(PartSpec, "partialspecialization",
60 "Partial Specialization", false, false);
62 // Specialize F by replacing the arguments (keys) in replacements with the
63 // constants (values). Replace all calls to F with those constants with
64 // a call to the specialized function. Returns the specialized function
66 SpecializeFunction(Function* F,
67 ValueMap<const Value*, Value*>& replacements) {
68 // arg numbers of deleted arguments
69 DenseMap<unsigned, const Argument*> deleted;
70 for (ValueMap<const Value*, Value*>::iterator
71 repb = replacements.begin(), repe = replacements.end();
72 repb != repe; ++repb) {
73 Argument const *arg = cast<const Argument>(repb->first);
74 deleted[arg->getArgNo()] = arg;
77 Function* NF = CloneFunction(F, replacements,
78 /*ModuleLevelChanges=*/false);
79 NF->setLinkage(GlobalValue::InternalLinkage);
80 F->getParent()->getFunctionList().push_back(NF);
82 for (Value::use_iterator ii = F->use_begin(), ee = F->use_end();
84 Value::use_iterator i = ii;
89 if (CS.getCalledFunction() == F) {
90 SmallVector<Value*, 6> args;
91 // Assemble the non-specialized arguments for the updated callsite.
92 // In the process, make sure that the specialized arguments are
93 // constant and match the specialization. If that's not the case,
94 // this callsite needs to call the original or some other
95 // specialization; don't change it here.
96 CallSite::arg_iterator as = CS.arg_begin(), ae = CS.arg_end();
97 for (CallSite::arg_iterator ai = as; ai != ae; ++ai) {
98 DenseMap<unsigned, const Argument*>::iterator delit = deleted.find(
99 std::distance(as, ai));
100 if (delit == deleted.end())
101 args.push_back(cast<Value>(ai));
103 Constant *ci = dyn_cast<Constant>(ai);
104 if (!(ci && ci == replacements[delit->second]))
109 if (CallInst *CI = dyn_cast<CallInst>(U)) {
110 NCall = CallInst::Create(NF, args.begin(), args.end(),
112 cast<CallInst>(NCall)->setTailCall(CI->isTailCall());
113 cast<CallInst>(NCall)->setCallingConv(CI->getCallingConv());
115 InvokeInst *II = cast<InvokeInst>(U);
116 NCall = InvokeInst::Create(NF, II->getNormalDest(),
118 args.begin(), args.end(),
120 cast<InvokeInst>(NCall)->setCallingConv(II->getCallingConv());
122 CS.getInstruction()->replaceAllUsesWith(NCall);
123 CS.getInstruction()->eraseFromParent();
133 bool PartSpec::runOnModule(Module &M) {
134 bool Changed = false;
135 for (Module::iterator I = M.begin(); I != M.end(); ++I) {
137 if (F.isDeclaration() || F.mayBeOverridden()) continue;
138 InterestingArgVector interestingArgs;
139 scanForInterest(F, interestingArgs);
141 // Find the first interesting Argument that we can specialize on
142 // If there are multiple interesting Arguments, then those will be found
143 // when processing the cloned function.
144 bool breakOuter = false;
145 for (unsigned int x = 0; !breakOuter && x < interestingArgs.size(); ++x) {
146 std::map<Constant*, int> distribution;
147 int total = scanDistribution(F, interestingArgs[x], distribution);
148 if (total > CallsMin)
149 for (std::map<Constant*, int>::iterator ii = distribution.begin(),
150 ee = distribution.end(); ii != ee; ++ii)
151 if (total > ii->second && ii->first &&
152 ii->second > total * ConstValPercent) {
153 ValueMap<const Value*, Value*> m;
154 Function::arg_iterator arg = F.arg_begin();
155 for (int y = 0; y < interestingArgs[x]; ++y)
157 m[&*arg] = ii->first;
158 SpecializeFunction(&F, m);
168 /// scanForInterest - This function decides which arguments would be worth
170 void PartSpec::scanForInterest(Function& F, InterestingArgVector& args) {
171 for(Function::arg_iterator ii = F.arg_begin(), ee = F.arg_end();
173 for(Value::use_iterator ui = ii->use_begin(), ue = ii->use_end();
176 bool interesting = false;
178 if (isa<CmpInst>(U)) interesting = true;
179 else if (isa<CallInst>(U))
180 interesting = ui->getOperand(0) == ii;
181 else if (isa<InvokeInst>(U))
182 interesting = ui->getOperand(0) == ii;
183 else if (isa<SwitchInst>(U)) interesting = true;
184 else if (isa<BranchInst>(U)) interesting = true;
187 args.push_back(std::distance(F.arg_begin(), ii));
194 /// scanDistribution - Construct a histogram of constants for arg of F at arg.
195 int PartSpec::scanDistribution(Function& F, int arg,
196 std::map<Constant*, int>& dist) {
197 bool hasIndirect = false;
199 for (Value::use_iterator ii = F.use_begin(), ee = F.use_end();
203 if (CS && CS.getCalledFunction() == &F) {
204 ++dist[dyn_cast<Constant>(CS.getArgument(arg))];
210 // Preserve the original address taken function even if all other uses
211 // will be specialized.
212 if (hasIndirect) ++total;
216 ModulePass* llvm::createPartialSpecializationPass() { return new PartSpec(); }