//===-- IPConstantPropagation.cpp - Propagate constants through calls -----===//
-//
+//
// The LLVM Compiler Infrastructure
//
-// This file was developed by the LLVM research group and is distributed under
-// the University of Illinois Open Source License. See LICENSE.TXT for details.
-//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
//===----------------------------------------------------------------------===//
//
// This pass implements an _extremely_ simple interprocedural constant
//
//===----------------------------------------------------------------------===//
+#define DEBUG_TYPE "ipconstprop"
#include "llvm/Transforms/IPO.h"
+#include "llvm/Constants.h"
+#include "llvm/Instructions.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
-#include "llvm/Constants.h"
#include "llvm/Support/CallSite.h"
+#include "llvm/Support/Compiler.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
-namespace {
- Statistic<> NumArgumentsProped("ipconstprop",
- "Number of args turned into constants");
+STATISTIC(NumArgumentsProped, "Number of args turned into constants");
+STATISTIC(NumReturnValProped, "Number of return values turned into constants");
+namespace {
/// IPCP - The interprocedural constant propagation pass
///
- struct IPCP : public ModulePass {
+ struct VISIBILITY_HIDDEN IPCP : public ModulePass {
+ static char ID; // Pass identification, replacement for typeid
+ IPCP() : ModulePass((intptr_t)&ID) {}
+
bool runOnModule(Module &M);
private:
- bool processFunction(Function &F);
+ bool PropagateConstantsIntoArguments(Function &F);
+ bool PropagateConstantReturn(Function &F);
};
- RegisterOpt<IPCP> X("ipconstprop", "Interprocedural constant propagation");
+ char IPCP::ID = 0;
+ RegisterPass<IPCP> X("ipconstprop", "Interprocedural constant propagation");
}
ModulePass *llvm::createIPConstantPropagationPass() { return new IPCP(); }
while (LocalChange) {
LocalChange = false;
for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
- if (!I->isExternal() && I->hasInternalLinkage())
- LocalChange |= processFunction(*I);
+ if (!I->isDeclaration()) {
+ // Delete any klingons.
+ I->removeDeadConstantUsers();
+ if (I->hasInternalLinkage())
+ LocalChange |= PropagateConstantsIntoArguments(*I);
+ Changed |= PropagateConstantReturn(*I);
+ }
Changed |= LocalChange;
}
return Changed;
}
-/// processFunction - Look at all uses of the specified function. If all uses
-/// are direct call sites, and all pass a particular constant in for an
-/// argument, propagate that constant in as the argument.
+/// PropagateConstantsIntoArguments - Look at all uses of the specified
+/// function. If all uses are direct call sites, and all pass a particular
+/// constant in for an argument, propagate that constant in as the argument.
///
-bool IPCP::processFunction(Function &F) {
- if (F.aempty() || F.use_empty()) return false; // No arguments? Early exit.
-
- // Delete any klingons.
- F.removeDeadConstantUsers();
+bool IPCP::PropagateConstantsIntoArguments(Function &F) {
+ if (F.arg_empty() || F.use_empty()) return false; // No arguments? Early exit.
std::vector<std::pair<Constant*, bool> > ArgumentConstants;
- ArgumentConstants.resize(F.asize());
+ ArgumentConstants.resize(F.arg_size());
unsigned NumNonconstant = 0;
return false; // Used by a non-instruction, do not transform
else {
CallSite CS = CallSite::get(cast<Instruction>(*I));
- if (CS.getInstruction() == 0 ||
+ if (CS.getInstruction() == 0 ||
CS.getCalledFunction() != &F)
return false; // Not a direct call site?
-
+
// Check out all of the potentially constant arguments
CallSite::arg_iterator AI = CS.arg_begin();
- Function::aiterator Arg = F.abegin();
+ Function::arg_iterator Arg = F.arg_begin();
for (unsigned i = 0, e = ArgumentConstants.size(); i != e;
++i, ++AI, ++Arg) {
if (*AI == &F) return false; // Passes the function into itself
// If we got to this point, there is a constant argument!
assert(NumNonconstant != ArgumentConstants.size());
- Function::aiterator AI = F.abegin();
+ Function::arg_iterator AI = F.arg_begin();
bool MadeChange = false;
for (unsigned i = 0, e = ArgumentConstants.size(); i != e; ++i, ++AI)
// Do we have a constant argument!?
- if (!ArgumentConstants[i].second) {
+ if (!ArgumentConstants[i].second && !AI->use_empty()) {
Value *V = ArgumentConstants[i].first;
if (V == 0) V = UndefValue::get(AI->getType());
AI->replaceAllUsesWith(V);
return MadeChange;
}
+
+// Check to see if this function returns a constant. If so, replace all callers
+// that user the return value with the returned valued. If we can replace ALL
+// callers,
+bool IPCP::PropagateConstantReturn(Function &F) {
+ if (F.getReturnType() == Type::VoidTy)
+ return false; // No return value.
+
+ // Check to see if this function returns a constant.
+ Value *RetVal = 0;
+ for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
+ if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
+ if (isa<UndefValue>(RI->getOperand(0))) {
+ // Ignore.
+ } else if (Constant *C = dyn_cast<Constant>(RI->getOperand(0))) {
+ if (RetVal == 0)
+ RetVal = C;
+ else if (RetVal != C)
+ return false; // Does not return the same constant.
+ } else {
+ return false; // Does not return a constant.
+ }
+ }
+
+ if (RetVal == 0) RetVal = UndefValue::get(F.getReturnType());
+
+ // If we got here, the function returns a constant value. Loop over all
+ // users, replacing any uses of the return value with the returned constant.
+ bool ReplacedAllUsers = true;
+ bool MadeChange = false;
+ for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I)
+ if (!isa<Instruction>(*I))
+ ReplacedAllUsers = false;
+ else {
+ CallSite CS = CallSite::get(cast<Instruction>(*I));
+ if (CS.getInstruction() == 0 ||
+ CS.getCalledFunction() != &F) {
+ ReplacedAllUsers = false;
+ } else {
+ if (!CS.getInstruction()->use_empty()) {
+ CS.getInstruction()->replaceAllUsesWith(RetVal);
+ MadeChange = true;
+ }
+ }
+ }
+
+ // If we replace all users with the returned constant, and there can be no
+ // other callers of the function, replace the constant being returned in the
+ // function with an undef value.
+ if (ReplacedAllUsers && F.hasInternalLinkage() && !isa<UndefValue>(RetVal)) {
+ Value *RV = UndefValue::get(RetVal->getType());
+ for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
+ if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
+ if (RI->getOperand(0) != RV) {
+ RI->setOperand(0, RV);
+ MadeChange = true;
+ }
+ }
+ }
+
+ if (MadeChange) ++NumReturnValProped;
+ return MadeChange;
+}
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