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https://github.com/c64scene-ar/llvm-6502.git
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3ed469ccd7
Turn on -Wunused and -Wno-unused-parameter. Clean up most of the resulting fall out by removing unused variables. Remaining warnings have to do with unused functions (I didn't want to delete code without review) and unused variables in generated code. Maintainers should clean up the remaining issues when they see them. All changes pass DejaGnu tests and Olden. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@31380 91177308-0d34-0410-b5e6-96231b3b80d8
557 lines
22 KiB
C++
557 lines
22 KiB
C++
//===-- ArgumentPromotion.cpp - Promote by-reference arguments ------------===//
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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 promotes "by reference" arguments to be "by value" arguments. In
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// practice, this means looking for internal functions that have pointer
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// arguments. If we can prove, through the use of alias analysis, that an
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// argument is *only* loaded, then we can pass the value into the function
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// instead of the address of the value. This can cause recursive simplification
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// of code and lead to the elimination of allocas (especially in C++ template
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// code like the STL).
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//
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// This pass also handles aggregate arguments that are passed into a function,
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// scalarizing them if the elements of the aggregate are only loaded. Note that
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// we refuse to scalarize aggregates which would require passing in more than
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// three operands to the function, because we don't want to pass thousands of
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// operands for a large array or structure!
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//
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// Note that this transformation could also be done for arguments that are only
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// stored to (returning the value instead), but we do not currently handle that
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// case. This case would be best handled when and if we start supporting
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// multiple return values from functions.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "argpromotion"
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#include "llvm/Transforms/IPO.h"
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#include "llvm/Constants.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Module.h"
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#include "llvm/CallGraphSCCPass.h"
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#include "llvm/Instructions.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/CallGraph.h"
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#include "llvm/Target/TargetData.h"
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#include "llvm/Support/CallSite.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/ADT/DepthFirstIterator.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/ADT/StringExtras.h"
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#include <iostream>
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#include <set>
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using namespace llvm;
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namespace {
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Statistic<> NumArgumentsPromoted("argpromotion",
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"Number of pointer arguments promoted");
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Statistic<> NumAggregatesPromoted("argpromotion",
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"Number of aggregate arguments promoted");
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Statistic<> NumArgumentsDead("argpromotion",
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"Number of dead pointer args eliminated");
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/// ArgPromotion - The 'by reference' to 'by value' argument promotion pass.
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///
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struct ArgPromotion : public CallGraphSCCPass {
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<AliasAnalysis>();
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AU.addRequired<TargetData>();
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CallGraphSCCPass::getAnalysisUsage(AU);
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}
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virtual bool runOnSCC(const std::vector<CallGraphNode *> &SCC);
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private:
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bool PromoteArguments(CallGraphNode *CGN);
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bool isSafeToPromoteArgument(Argument *Arg) const;
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Function *DoPromotion(Function *F, std::vector<Argument*> &ArgsToPromote);
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};
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RegisterPass<ArgPromotion> X("argpromotion",
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"Promote 'by reference' arguments to scalars");
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}
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ModulePass *llvm::createArgumentPromotionPass() {
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return new ArgPromotion();
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}
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bool ArgPromotion::runOnSCC(const std::vector<CallGraphNode *> &SCC) {
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bool Changed = false, LocalChange;
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do { // Iterate until we stop promoting from this SCC.
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LocalChange = false;
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// Attempt to promote arguments from all functions in this SCC.
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for (unsigned i = 0, e = SCC.size(); i != e; ++i)
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LocalChange |= PromoteArguments(SCC[i]);
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Changed |= LocalChange; // Remember that we changed something.
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} while (LocalChange);
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return Changed;
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}
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/// PromoteArguments - This method checks the specified function to see if there
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/// are any promotable arguments and if it is safe to promote the function (for
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/// example, all callers are direct). If safe to promote some arguments, it
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/// calls the DoPromotion method.
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///
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bool ArgPromotion::PromoteArguments(CallGraphNode *CGN) {
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Function *F = CGN->getFunction();
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// Make sure that it is local to this module.
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if (!F || !F->hasInternalLinkage()) return false;
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// First check: see if there are any pointer arguments! If not, quick exit.
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std::vector<Argument*> PointerArgs;
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for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I)
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if (isa<PointerType>(I->getType()))
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PointerArgs.push_back(I);
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if (PointerArgs.empty()) return false;
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// Second check: make sure that all callers are direct callers. We can't
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// transform functions that have indirect callers.
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for (Value::use_iterator UI = F->use_begin(), E = F->use_end();
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UI != E; ++UI) {
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CallSite CS = CallSite::get(*UI);
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if (!CS.getInstruction()) // "Taking the address" of the function
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return false;
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// Ensure that this call site is CALLING the function, not passing it as
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// an argument.
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for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
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AI != E; ++AI)
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if (*AI == F) return false; // Passing the function address in!
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}
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// Check to see which arguments are promotable. If an argument is not
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// promotable, remove it from the PointerArgs vector.
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for (unsigned i = 0; i != PointerArgs.size(); ++i)
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if (!isSafeToPromoteArgument(PointerArgs[i])) {
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std::swap(PointerArgs[i--], PointerArgs.back());
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PointerArgs.pop_back();
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}
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// No promotable pointer arguments.
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if (PointerArgs.empty()) return false;
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// Okay, promote all of the arguments are rewrite the callees!
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Function *NewF = DoPromotion(F, PointerArgs);
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// Update the call graph to know that the old function is gone.
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getAnalysis<CallGraph>().changeFunction(F, NewF);
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return true;
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}
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/// IsAlwaysValidPointer - Return true if the specified pointer is always legal
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/// to load.
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static bool IsAlwaysValidPointer(Value *V) {
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if (isa<AllocaInst>(V) || isa<GlobalVariable>(V)) return true;
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if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V))
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return IsAlwaysValidPointer(GEP->getOperand(0));
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if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
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if (CE->getOpcode() == Instruction::GetElementPtr)
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return IsAlwaysValidPointer(CE->getOperand(0));
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return false;
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}
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/// AllCalleesPassInValidPointerForArgument - Return true if we can prove that
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/// all callees pass in a valid pointer for the specified function argument.
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static bool AllCalleesPassInValidPointerForArgument(Argument *Arg) {
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Function *Callee = Arg->getParent();
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unsigned ArgNo = std::distance(Callee->arg_begin(), Function::arg_iterator(Arg));
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// Look at all call sites of the function. At this pointer we know we only
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// have direct callees.
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for (Value::use_iterator UI = Callee->use_begin(), E = Callee->use_end();
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UI != E; ++UI) {
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CallSite CS = CallSite::get(*UI);
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assert(CS.getInstruction() && "Should only have direct calls!");
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if (!IsAlwaysValidPointer(CS.getArgument(ArgNo)))
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return false;
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}
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return true;
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}
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/// isSafeToPromoteArgument - As you might guess from the name of this method,
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/// it checks to see if it is both safe and useful to promote the argument.
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/// This method limits promotion of aggregates to only promote up to three
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/// elements of the aggregate in order to avoid exploding the number of
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/// arguments passed in.
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bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg) const {
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// We can only promote this argument if all of the uses are loads, or are GEP
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// instructions (with constant indices) that are subsequently loaded.
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bool HasLoadInEntryBlock = false;
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BasicBlock *EntryBlock = Arg->getParent()->begin();
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std::vector<LoadInst*> Loads;
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std::vector<std::vector<ConstantInt*> > GEPIndices;
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for (Value::use_iterator UI = Arg->use_begin(), E = Arg->use_end();
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UI != E; ++UI)
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if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
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if (LI->isVolatile()) return false; // Don't hack volatile loads
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Loads.push_back(LI);
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HasLoadInEntryBlock |= LI->getParent() == EntryBlock;
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} else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(*UI)) {
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if (GEP->use_empty()) {
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// Dead GEP's cause trouble later. Just remove them if we run into
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// them.
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getAnalysis<AliasAnalysis>().deleteValue(GEP);
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GEP->getParent()->getInstList().erase(GEP);
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return isSafeToPromoteArgument(Arg);
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}
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// Ensure that all of the indices are constants.
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std::vector<ConstantInt*> Operands;
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for (unsigned i = 1, e = GEP->getNumOperands(); i != e; ++i)
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if (ConstantInt *C = dyn_cast<ConstantInt>(GEP->getOperand(i)))
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Operands.push_back(C);
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else
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return false; // Not a constant operand GEP!
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// Ensure that the only users of the GEP are load instructions.
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for (Value::use_iterator UI = GEP->use_begin(), E = GEP->use_end();
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UI != E; ++UI)
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if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
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if (LI->isVolatile()) return false; // Don't hack volatile loads
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Loads.push_back(LI);
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HasLoadInEntryBlock |= LI->getParent() == EntryBlock;
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} else {
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return false;
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}
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// See if there is already a GEP with these indices. If not, check to
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// make sure that we aren't promoting too many elements. If so, nothing
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// to do.
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if (std::find(GEPIndices.begin(), GEPIndices.end(), Operands) ==
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GEPIndices.end()) {
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if (GEPIndices.size() == 3) {
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DEBUG(std::cerr << "argpromotion disable promoting argument '"
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<< Arg->getName() << "' because it would require adding more "
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<< "than 3 arguments to the function.\n");
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// We limit aggregate promotion to only promoting up to three elements
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// of the aggregate.
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return false;
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}
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GEPIndices.push_back(Operands);
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}
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} else {
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return false; // Not a load or a GEP.
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}
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if (Loads.empty()) return true; // No users, this is a dead argument.
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// If we decide that we want to promote this argument, the value is going to
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// be unconditionally loaded in all callees. This is only safe to do if the
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// pointer was going to be unconditionally loaded anyway (i.e. there is a load
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// of the pointer in the entry block of the function) or if we can prove that
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// all pointers passed in are always to legal locations (for example, no null
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// pointers are passed in, no pointers to free'd memory, etc).
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if (!HasLoadInEntryBlock && !AllCalleesPassInValidPointerForArgument(Arg))
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return false; // Cannot prove that this is safe!!
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// Okay, now we know that the argument is only used by load instructions and
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// it is safe to unconditionally load the pointer. Use alias analysis to
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// check to see if the pointer is guaranteed to not be modified from entry of
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// the function to each of the load instructions.
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// Because there could be several/many load instructions, remember which
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// blocks we know to be transparent to the load.
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std::set<BasicBlock*> TranspBlocks;
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AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
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TargetData &TD = getAnalysis<TargetData>();
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for (unsigned i = 0, e = Loads.size(); i != e; ++i) {
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// Check to see if the load is invalidated from the start of the block to
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// the load itself.
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LoadInst *Load = Loads[i];
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BasicBlock *BB = Load->getParent();
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const PointerType *LoadTy =
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cast<PointerType>(Load->getOperand(0)->getType());
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unsigned LoadSize = (unsigned)TD.getTypeSize(LoadTy->getElementType());
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if (AA.canInstructionRangeModify(BB->front(), *Load, Arg, LoadSize))
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return false; // Pointer is invalidated!
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// Now check every path from the entry block to the load for transparency.
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// To do this, we perform a depth first search on the inverse CFG from the
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// loading block.
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for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
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for (idf_ext_iterator<BasicBlock*> I = idf_ext_begin(*PI, TranspBlocks),
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E = idf_ext_end(*PI, TranspBlocks); I != E; ++I)
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if (AA.canBasicBlockModify(**I, Arg, LoadSize))
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return false;
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}
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// If the path from the entry of the function to each load is free of
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// instructions that potentially invalidate the load, we can make the
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// transformation!
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return true;
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}
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namespace {
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/// GEPIdxComparator - Provide a strong ordering for GEP indices. All Value*
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/// elements are instances of ConstantInt.
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///
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struct GEPIdxComparator {
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bool operator()(const std::vector<Value*> &LHS,
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const std::vector<Value*> &RHS) const {
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unsigned idx = 0;
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for (; idx < LHS.size() && idx < RHS.size(); ++idx) {
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if (LHS[idx] != RHS[idx]) {
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return cast<ConstantInt>(LHS[idx])->getZExtValue() <
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cast<ConstantInt>(RHS[idx])->getZExtValue();
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}
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}
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// Return less than if we ran out of stuff in LHS and we didn't run out of
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// stuff in RHS.
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return idx == LHS.size() && idx != RHS.size();
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}
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};
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}
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/// DoPromotion - This method actually performs the promotion of the specified
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/// arguments, and returns the new function. At this point, we know that it's
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/// safe to do so.
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Function *ArgPromotion::DoPromotion(Function *F,
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std::vector<Argument*> &Args2Prom) {
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std::set<Argument*> ArgsToPromote(Args2Prom.begin(), Args2Prom.end());
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// Start by computing a new prototype for the function, which is the same as
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// the old function, but has modified arguments.
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const FunctionType *FTy = F->getFunctionType();
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std::vector<const Type*> Params;
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typedef std::set<std::vector<Value*>, GEPIdxComparator> ScalarizeTable;
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// ScalarizedElements - If we are promoting a pointer that has elements
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// accessed out of it, keep track of which elements are accessed so that we
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// can add one argument for each.
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//
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// Arguments that are directly loaded will have a zero element value here, to
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// handle cases where there are both a direct load and GEP accesses.
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//
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std::map<Argument*, ScalarizeTable> ScalarizedElements;
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// OriginalLoads - Keep track of a representative load instruction from the
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// original function so that we can tell the alias analysis implementation
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// what the new GEP/Load instructions we are inserting look like.
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std::map<std::vector<Value*>, LoadInst*> OriginalLoads;
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for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I)
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if (!ArgsToPromote.count(I)) {
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Params.push_back(I->getType());
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} else if (I->use_empty()) {
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++NumArgumentsDead;
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} else {
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// Okay, this is being promoted. Check to see if there are any GEP uses
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// of the argument.
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ScalarizeTable &ArgIndices = ScalarizedElements[I];
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for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
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++UI) {
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Instruction *User = cast<Instruction>(*UI);
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assert(isa<LoadInst>(User) || isa<GetElementPtrInst>(User));
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std::vector<Value*> Indices(User->op_begin()+1, User->op_end());
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ArgIndices.insert(Indices);
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LoadInst *OrigLoad;
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if (LoadInst *L = dyn_cast<LoadInst>(User))
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OrigLoad = L;
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else
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OrigLoad = cast<LoadInst>(User->use_back());
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OriginalLoads[Indices] = OrigLoad;
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}
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// Add a parameter to the function for each element passed in.
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for (ScalarizeTable::iterator SI = ArgIndices.begin(),
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E = ArgIndices.end(); SI != E; ++SI)
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Params.push_back(GetElementPtrInst::getIndexedType(I->getType(), *SI));
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if (ArgIndices.size() == 1 && ArgIndices.begin()->empty())
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++NumArgumentsPromoted;
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else
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++NumAggregatesPromoted;
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}
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const Type *RetTy = FTy->getReturnType();
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// Work around LLVM bug PR56: the CWriter cannot emit varargs functions which
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// have zero fixed arguments.
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bool ExtraArgHack = false;
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if (Params.empty() && FTy->isVarArg()) {
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ExtraArgHack = true;
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Params.push_back(Type::IntTy);
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}
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FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg());
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// Create the new function body and insert it into the module...
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Function *NF = new Function(NFTy, F->getLinkage(), F->getName());
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NF->setCallingConv(F->getCallingConv());
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F->getParent()->getFunctionList().insert(F, NF);
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// Get the alias analysis information that we need to update to reflect our
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// changes.
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AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
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// Loop over all of the callers of the function, transforming the call sites
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// to pass in the loaded pointers.
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//
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std::vector<Value*> Args;
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while (!F->use_empty()) {
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CallSite CS = CallSite::get(F->use_back());
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Instruction *Call = CS.getInstruction();
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// Loop over the operands, inserting GEP and loads in the caller as
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// appropriate.
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CallSite::arg_iterator AI = CS.arg_begin();
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for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
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I != E; ++I, ++AI)
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if (!ArgsToPromote.count(I))
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Args.push_back(*AI); // Unmodified argument
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else if (!I->use_empty()) {
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// Non-dead argument: insert GEPs and loads as appropriate.
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ScalarizeTable &ArgIndices = ScalarizedElements[I];
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for (ScalarizeTable::iterator SI = ArgIndices.begin(),
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E = ArgIndices.end(); SI != E; ++SI) {
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Value *V = *AI;
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LoadInst *OrigLoad = OriginalLoads[*SI];
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if (!SI->empty()) {
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V = new GetElementPtrInst(V, *SI, V->getName()+".idx", Call);
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AA.copyValue(OrigLoad->getOperand(0), V);
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}
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Args.push_back(new LoadInst(V, V->getName()+".val", Call));
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AA.copyValue(OrigLoad, Args.back());
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}
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}
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if (ExtraArgHack)
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Args.push_back(Constant::getNullValue(Type::IntTy));
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// Push any varargs arguments on the list
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for (; AI != CS.arg_end(); ++AI)
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Args.push_back(*AI);
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Instruction *New;
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if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
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New = new InvokeInst(NF, II->getNormalDest(), II->getUnwindDest(),
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Args, "", Call);
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cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
|
|
} else {
|
|
New = new CallInst(NF, Args, "", Call);
|
|
cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
|
|
if (cast<CallInst>(Call)->isTailCall())
|
|
cast<CallInst>(New)->setTailCall();
|
|
}
|
|
Args.clear();
|
|
|
|
// Update the alias analysis implementation to know that we are replacing
|
|
// the old call with a new one.
|
|
AA.replaceWithNewValue(Call, New);
|
|
|
|
if (!Call->use_empty()) {
|
|
Call->replaceAllUsesWith(New);
|
|
std::string Name = Call->getName();
|
|
Call->setName("");
|
|
New->setName(Name);
|
|
}
|
|
|
|
// Finally, remove the old call from the program, reducing the use-count of
|
|
// F.
|
|
Call->getParent()->getInstList().erase(Call);
|
|
}
|
|
|
|
// Since we have now created the new function, splice the body of the old
|
|
// function right into the new function, leaving the old rotting hulk of the
|
|
// function empty.
|
|
NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
|
|
|
|
// Loop over the argument list, transfering uses of the old arguments over to
|
|
// the new arguments, also transfering over the names as well.
|
|
//
|
|
for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), I2 = NF->arg_begin();
|
|
I != E; ++I)
|
|
if (!ArgsToPromote.count(I)) {
|
|
// If this is an unmodified argument, move the name and users over to the
|
|
// new version.
|
|
I->replaceAllUsesWith(I2);
|
|
I2->setName(I->getName());
|
|
AA.replaceWithNewValue(I, I2);
|
|
++I2;
|
|
} else if (I->use_empty()) {
|
|
AA.deleteValue(I);
|
|
} else {
|
|
// Otherwise, if we promoted this argument, then all users are load
|
|
// instructions, and all loads should be using the new argument that we
|
|
// added.
|
|
ScalarizeTable &ArgIndices = ScalarizedElements[I];
|
|
|
|
while (!I->use_empty()) {
|
|
if (LoadInst *LI = dyn_cast<LoadInst>(I->use_back())) {
|
|
assert(ArgIndices.begin()->empty() &&
|
|
"Load element should sort to front!");
|
|
I2->setName(I->getName()+".val");
|
|
LI->replaceAllUsesWith(I2);
|
|
AA.replaceWithNewValue(LI, I2);
|
|
LI->getParent()->getInstList().erase(LI);
|
|
DEBUG(std::cerr << "*** Promoted load of argument '" << I->getName()
|
|
<< "' in function '" << F->getName() << "'\n");
|
|
} else {
|
|
GetElementPtrInst *GEP = cast<GetElementPtrInst>(I->use_back());
|
|
std::vector<Value*> Operands(GEP->op_begin()+1, GEP->op_end());
|
|
|
|
Function::arg_iterator TheArg = I2;
|
|
for (ScalarizeTable::iterator It = ArgIndices.begin();
|
|
*It != Operands; ++It, ++TheArg) {
|
|
assert(It != ArgIndices.end() && "GEP not handled??");
|
|
}
|
|
|
|
std::string NewName = I->getName();
|
|
for (unsigned i = 0, e = Operands.size(); i != e; ++i)
|
|
if (ConstantInt *CI = dyn_cast<ConstantInt>(Operands[i]))
|
|
NewName += "."+itostr((int64_t)CI->getZExtValue());
|
|
else
|
|
NewName += ".x";
|
|
TheArg->setName(NewName+".val");
|
|
|
|
DEBUG(std::cerr << "*** Promoted agg argument '" << TheArg->getName()
|
|
<< "' of function '" << F->getName() << "'\n");
|
|
|
|
// All of the uses must be load instructions. Replace them all with
|
|
// the argument specified by ArgNo.
|
|
while (!GEP->use_empty()) {
|
|
LoadInst *L = cast<LoadInst>(GEP->use_back());
|
|
L->replaceAllUsesWith(TheArg);
|
|
AA.replaceWithNewValue(L, TheArg);
|
|
L->getParent()->getInstList().erase(L);
|
|
}
|
|
AA.deleteValue(GEP);
|
|
GEP->getParent()->getInstList().erase(GEP);
|
|
}
|
|
}
|
|
|
|
// Increment I2 past all of the arguments added for this promoted pointer.
|
|
for (unsigned i = 0, e = ArgIndices.size(); i != e; ++i)
|
|
++I2;
|
|
}
|
|
|
|
// Notify the alias analysis implementation that we inserted a new argument.
|
|
if (ExtraArgHack)
|
|
AA.copyValue(Constant::getNullValue(Type::IntTy), NF->arg_begin());
|
|
|
|
|
|
// Tell the alias analysis that the old function is about to disappear.
|
|
AA.replaceWithNewValue(F, NF);
|
|
|
|
// Now that the old function is dead, delete it.
|
|
F->getParent()->getFunctionList().erase(F);
|
|
return NF;
|
|
}
|