| //===-- 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 pass implements an _extremely_ simple interprocedural constant |
| // propagation pass. It could certainly be improved in many different ways, |
| // like using a worklist. This pass makes arguments dead, but does not remove |
| // them. The existing dead argument elimination pass should be run after this |
| // to clean up the mess. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Transforms/IPO.h" |
| #include "llvm/Module.h" |
| #include "llvm/Pass.h" |
| #include "llvm/Constants.h" |
| #include "llvm/Support/CallSite.h" |
| #include "Support/Statistic.h" |
| |
| namespace llvm { |
| |
| namespace { |
| Statistic<> NumArgumentsProped("ipconstprop", |
| "Number of args turned into constants"); |
| |
| /// IPCP - The interprocedural constant propagation pass |
| /// |
| struct IPCP : public Pass { |
| bool run(Module &M); |
| private: |
| bool processFunction(Function &F); |
| }; |
| RegisterOpt<IPCP> X("ipconstprop", "Interprocedural constant propagation"); |
| } |
| |
| Pass *createIPConstantPropagationPass() { return new IPCP(); } |
| |
| bool IPCP::run(Module &M) { |
| bool Changed = false; |
| bool LocalChange = true; |
| |
| // FIXME: instead of using smart algorithms, we just iterate until we stop |
| // making changes. |
| while (LocalChange) { |
| LocalChange = false; |
| for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) |
| if (!I->isExternal() && I->hasInternalLinkage()) |
| LocalChange |= processFunction(*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. |
| /// |
| bool IPCP::processFunction(Function &F) { |
| if (F.aempty() || F.use_empty()) return false; // No arguments? Early exit. |
| |
| std::vector<std::pair<Constant*, bool> > ArgumentConstants; |
| ArgumentConstants.resize(F.asize()); |
| |
| unsigned NumNonconstant = 0; |
| |
| for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I) |
| if (!isa<Instruction>(*I)) |
| return false; // Used by a non-instruction, do not transform |
| else { |
| CallSite CS = CallSite::get(cast<Instruction>(*I)); |
| 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(); |
| for (unsigned i = 0, e = ArgumentConstants.size(); i != e; ++i, ++AI) { |
| if (*AI == &F) return false; // Passes the function into itself |
| |
| if (!ArgumentConstants[i].second) { |
| if (isa<Constant>(*AI) || isa<GlobalValue>(*AI)) { |
| Constant *C = dyn_cast<Constant>(*AI); |
| if (!C) C = ConstantPointerRef::get(cast<GlobalValue>(*AI)); |
| |
| if (!ArgumentConstants[i].first) |
| ArgumentConstants[i].first = C; |
| else if (ArgumentConstants[i].first != C) { |
| // Became non-constant |
| ArgumentConstants[i].second = true; |
| ++NumNonconstant; |
| if (NumNonconstant == ArgumentConstants.size()) return false; |
| } |
| } else { |
| // This is not a constant argument. Mark the argument as |
| // non-constant. |
| ArgumentConstants[i].second = true; |
| ++NumNonconstant; |
| if (NumNonconstant == ArgumentConstants.size()) return false; |
| } |
| } |
| } |
| } |
| |
| // If we got to this point, there is a constant argument! |
| assert(NumNonconstant != ArgumentConstants.size()); |
| Function::aiterator AI = F.abegin(); |
| bool MadeChange = false; |
| for (unsigned i = 0, e = ArgumentConstants.size(); i != e; ++i, ++AI) |
| // Do we have a constant argument!? |
| if (!ArgumentConstants[i].second && !AI->use_empty()) { |
| assert(ArgumentConstants[i].first && "Unknown constant value!"); |
| Value *V = ArgumentConstants[i].first; |
| if (ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(V)) |
| V = CPR->getValue(); |
| AI->replaceAllUsesWith(V); |
| ++NumArgumentsProped; |
| MadeChange = true; |
| } |
| return MadeChange; |
| } |
| |
| } // End llvm namespace |