forked from OSchip/llvm-project
127 lines
4.5 KiB
C++
127 lines
4.5 KiB
C++
//===-- IPConstantPropagation.cpp - Propagate constants through calls -----===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass implements an _extremely_ simple interprocedural constant
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// propagation pass. It could certainly be improved in many different ways,
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// like using a worklist. This pass makes arguments dead, but does not remove
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// them. The existing dead argument elimination pass should be run after this
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// to clean up the mess.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/IPO.h"
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#include "llvm/Module.h"
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#include "llvm/Pass.h"
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#include "llvm/Constants.h"
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#include "llvm/Support/CallSite.h"
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#include "Support/Statistic.h"
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using namespace llvm;
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namespace {
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Statistic<> NumArgumentsProped("ipconstprop",
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"Number of args turned into constants");
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/// IPCP - The interprocedural constant propagation pass
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///
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struct IPCP : public Pass {
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bool run(Module &M);
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private:
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bool processFunction(Function &F);
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};
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RegisterOpt<IPCP> X("ipconstprop", "Interprocedural constant propagation");
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}
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Pass *llvm::createIPConstantPropagationPass() { return new IPCP(); }
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bool IPCP::run(Module &M) {
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bool Changed = false;
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bool LocalChange = true;
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// FIXME: instead of using smart algorithms, we just iterate until we stop
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// making changes.
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while (LocalChange) {
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LocalChange = false;
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for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
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if (!I->isExternal() && I->hasInternalLinkage())
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LocalChange |= processFunction(*I);
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Changed |= LocalChange;
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}
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return Changed;
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}
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/// processFunction - Look at all uses of the specified function. If all uses
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/// are direct call sites, and all pass a particular constant in for an
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/// argument, propagate that constant in as the argument.
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///
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bool IPCP::processFunction(Function &F) {
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if (F.aempty() || F.use_empty()) return false; // No arguments? Early exit.
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std::vector<std::pair<Constant*, bool> > ArgumentConstants;
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ArgumentConstants.resize(F.asize());
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unsigned NumNonconstant = 0;
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for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I)
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if (!isa<Instruction>(*I))
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return false; // Used by a non-instruction, do not transform
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else {
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CallSite CS = CallSite::get(cast<Instruction>(*I));
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if (CS.getInstruction() == 0 ||
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CS.getCalledFunction() != &F)
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return false; // Not a direct call site?
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// Check out all of the potentially constant arguments
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CallSite::arg_iterator AI = CS.arg_begin();
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for (unsigned i = 0, e = ArgumentConstants.size(); i != e; ++i, ++AI) {
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if (*AI == &F) return false; // Passes the function into itself
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if (!ArgumentConstants[i].second) {
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if (isa<Constant>(*AI) || isa<GlobalValue>(*AI)) {
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Constant *C = dyn_cast<Constant>(*AI);
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if (!C) C = ConstantPointerRef::get(cast<GlobalValue>(*AI));
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if (!ArgumentConstants[i].first)
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ArgumentConstants[i].first = C;
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else if (ArgumentConstants[i].first != C) {
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// Became non-constant
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ArgumentConstants[i].second = true;
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++NumNonconstant;
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if (NumNonconstant == ArgumentConstants.size()) return false;
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}
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} else {
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// This is not a constant argument. Mark the argument as
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// non-constant.
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ArgumentConstants[i].second = true;
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++NumNonconstant;
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if (NumNonconstant == ArgumentConstants.size()) return false;
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}
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}
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}
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}
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// If we got to this point, there is a constant argument!
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assert(NumNonconstant != ArgumentConstants.size());
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Function::aiterator AI = F.abegin();
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bool MadeChange = false;
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for (unsigned i = 0, e = ArgumentConstants.size(); i != e; ++i, ++AI)
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// Do we have a constant argument!?
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if (!ArgumentConstants[i].second && !AI->use_empty()) {
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assert(ArgumentConstants[i].first && "Unknown constant value!");
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Value *V = ArgumentConstants[i].first;
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if (ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(V))
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V = CPR->getValue();
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AI->replaceAllUsesWith(V);
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++NumArgumentsProped;
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MadeChange = true;
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}
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return MadeChange;
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}
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