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https://github.com/c64scene-ar/llvm-6502.git
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@62279 91177308-0d34-0410-b5e6-96231b3b80d8
378 lines
12 KiB
C++
378 lines
12 KiB
C++
//===- MergeFunctions.cpp - Merge identical functions ---------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass looks for equivalent functions that are mergable and folds them.
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//
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// A Function will not be analyzed if:
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// * it is overridable at runtime (except for weak linkage), or
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// * it is used by anything other than the callee parameter of a call/invoke
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//
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// A hash is computed from the function, based on its type and number of
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// basic blocks.
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//
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// Once all hashes are computed, we perform an expensive equality comparison
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// on each function pair. This takes n^2/2 comparisons per bucket, so it's
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// important that the hash function be high quality. The equality comparison
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// iterates through each instruction in each basic block.
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//
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// When a match is found, the functions are folded. We can only fold two
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// functions when we know that the definition of one of them is not
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// overridable.
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// * fold a function marked internal by replacing all of its users.
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// * fold extern or weak functions by replacing them with a global alias
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//
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//===----------------------------------------------------------------------===//
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//
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// Future work:
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//
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// * fold vector<T*>::push_back and vector<S*>::push_back.
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//
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// These two functions have different types, but in a way that doesn't matter
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// to us. As long as we never see an S or T itself, using S* and S** is the
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// same as using a T* and T**.
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//
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// * virtual functions.
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//
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// Many functions have their address taken by the virtual function table for
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// the object they belong to. However, as long as it's only used for a lookup
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// and call, this is irrelevant, and we'd like to fold such implementations.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "mergefunc"
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#include "llvm/Transforms/IPO.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Constants.h"
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#include "llvm/InlineAsm.h"
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#include "llvm/Instructions.h"
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#include "llvm/Module.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/CallSite.h"
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#include "llvm/Support/Compiler.h"
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#include "llvm/Support/Debug.h"
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#include <map>
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#include <vector>
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using namespace llvm;
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STATISTIC(NumFunctionsMerged, "Number of functions merged");
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STATISTIC(NumMergeFails, "Number of identical function pairings not merged");
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namespace {
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struct VISIBILITY_HIDDEN MergeFunctions : public ModulePass {
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static char ID; // Pass identification, replacement for typeid
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MergeFunctions() : ModulePass((intptr_t)&ID) {}
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bool runOnModule(Module &M);
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};
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}
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char MergeFunctions::ID = 0;
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static RegisterPass<MergeFunctions>
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X("mergefunc", "Merge Functions");
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ModulePass *llvm::createMergeFunctionsPass() {
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return new MergeFunctions();
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}
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static unsigned long hash(const Function *F) {
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return F->size() ^ reinterpret_cast<unsigned long>(F->getType());
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//return F->size() ^ F->arg_size() ^ F->getReturnType();
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}
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static bool compare(const Value *V, const Value *U) {
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assert(!isa<BasicBlock>(V) && !isa<BasicBlock>(U) &&
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"Must not compare basic blocks.");
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assert(V->getType() == U->getType() &&
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"Two of the same operation have operands of different type.");
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// TODO: If the constant is an expression of F, we should accept that it's
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// equal to the same expression in terms of G.
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if (isa<Constant>(V))
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return V == U;
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// The caller has ensured that ValueMap[V] != U. Since Arguments are
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// pre-loaded into the ValueMap, and Instructions are added as we go, we know
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// that this can only be a mis-match.
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if (isa<Instruction>(V) || isa<Argument>(V))
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return false;
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if (isa<InlineAsm>(V) && isa<InlineAsm>(U)) {
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const InlineAsm *IAF = cast<InlineAsm>(V);
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const InlineAsm *IAG = cast<InlineAsm>(U);
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return IAF->getAsmString() == IAG->getAsmString() &&
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IAF->getConstraintString() == IAG->getConstraintString();
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}
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return false;
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}
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static bool equals(const BasicBlock *BB1, const BasicBlock *BB2,
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DenseMap<const Value *, const Value *> &ValueMap,
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DenseMap<const Value *, const Value *> &SpeculationMap) {
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// Specutively add it anyways. If it's false, we'll notice a difference later, and
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// this won't matter.
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ValueMap[BB1] = BB2;
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BasicBlock::const_iterator FI = BB1->begin(), FE = BB1->end();
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BasicBlock::const_iterator GI = BB2->begin(), GE = BB2->end();
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do {
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if (!FI->isSameOperationAs(const_cast<Instruction *>(&*GI)))
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return false;
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if (FI->getNumOperands() != GI->getNumOperands())
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return false;
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if (ValueMap[FI] == GI) {
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++FI, ++GI;
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continue;
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}
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if (ValueMap[FI] != NULL)
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return false;
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for (unsigned i = 0, e = FI->getNumOperands(); i != e; ++i) {
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Value *OpF = FI->getOperand(i);
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Value *OpG = GI->getOperand(i);
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if (ValueMap[OpF] == OpG)
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continue;
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if (ValueMap[OpF] != NULL)
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return false;
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assert(OpF->getType() == OpG->getType() &&
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"Two of the same operation has operands of different type.");
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if (OpF->getValueID() != OpG->getValueID())
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return false;
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if (isa<PHINode>(FI)) {
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if (SpeculationMap[OpF] == NULL)
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SpeculationMap[OpF] = OpG;
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else if (SpeculationMap[OpF] != OpG)
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return false;
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continue;
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} else if (isa<BasicBlock>(OpF)) {
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assert(isa<TerminatorInst>(FI) &&
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"BasicBlock referenced by non-Terminator non-PHI");
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// This call changes the ValueMap, hence we can't use
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// Value *& = ValueMap[...]
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if (!equals(cast<BasicBlock>(OpF), cast<BasicBlock>(OpG), ValueMap,
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SpeculationMap))
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return false;
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} else {
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if (!compare(OpF, OpG))
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return false;
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}
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ValueMap[OpF] = OpG;
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}
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ValueMap[FI] = GI;
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++FI, ++GI;
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} while (FI != FE && GI != GE);
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return FI == FE && GI == GE;
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}
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static bool equals(const Function *F, const Function *G) {
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// We need to recheck everything, but check the things that weren't included
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// in the hash first.
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if (F->getAttributes() != G->getAttributes())
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return false;
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if (F->hasGC() != G->hasGC())
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return false;
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if (F->hasGC() && F->getGC() != G->getGC())
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return false;
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if (F->hasSection() != G->hasSection())
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return false;
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if (F->hasSection() && F->getSection() != G->getSection())
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return false;
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// TODO: if it's internal and only used in direct calls, we could handle this
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// case too.
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if (F->getCallingConv() != G->getCallingConv())
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return false;
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// TODO: We want to permit cases where two functions take T* and S* but
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// only load or store them into T** and S**.
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if (F->getType() != G->getType())
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return false;
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DenseMap<const Value *, const Value *> ValueMap;
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DenseMap<const Value *, const Value *> SpeculationMap;
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ValueMap[F] = G;
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assert(F->arg_size() == G->arg_size() &&
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"Identical functions have a different number of args.");
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for (Function::const_arg_iterator fi = F->arg_begin(), gi = G->arg_begin(),
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fe = F->arg_end(); fi != fe; ++fi, ++gi)
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ValueMap[fi] = gi;
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if (!equals(&F->getEntryBlock(), &G->getEntryBlock(), ValueMap,
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SpeculationMap))
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return false;
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for (DenseMap<const Value *, const Value *>::iterator
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I = SpeculationMap.begin(), E = SpeculationMap.end(); I != E; ++I) {
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if (ValueMap[I->first] != I->second)
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return false;
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}
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return true;
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}
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static bool fold(std::vector<Function *> &FnVec, unsigned i, unsigned j) {
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if (FnVec[i]->mayBeOverridden() && !FnVec[j]->mayBeOverridden())
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std::swap(FnVec[i], FnVec[j]);
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Function *F = FnVec[i];
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Function *G = FnVec[j];
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if (!F->mayBeOverridden()) {
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if (G->hasLocalLinkage()) {
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F->setAlignment(std::max(F->getAlignment(), G->getAlignment()));
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G->replaceAllUsesWith(F);
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G->eraseFromParent();
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++NumFunctionsMerged;
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return true;
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}
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if (G->hasExternalLinkage() || G->hasWeakLinkage()) {
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GlobalAlias *GA = new GlobalAlias(G->getType(), G->getLinkage(), "",
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F, G->getParent());
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F->setAlignment(std::max(F->getAlignment(), G->getAlignment()));
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GA->takeName(G);
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GA->setVisibility(G->getVisibility());
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G->replaceAllUsesWith(GA);
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G->eraseFromParent();
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++NumFunctionsMerged;
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return true;
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}
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}
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if (F->hasWeakLinkage() && G->hasWeakLinkage()) {
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GlobalAlias *GA_F = new GlobalAlias(F->getType(), F->getLinkage(), "",
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0, F->getParent());
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GA_F->takeName(F);
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GA_F->setVisibility(F->getVisibility());
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F->setAlignment(std::max(F->getAlignment(), G->getAlignment()));
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F->replaceAllUsesWith(GA_F);
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F->setName("folded." + GA_F->getName());
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F->setLinkage(GlobalValue::ExternalLinkage);
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GA_F->setAliasee(F);
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GlobalAlias *GA_G = new GlobalAlias(G->getType(), G->getLinkage(), "",
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F, G->getParent());
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GA_G->takeName(G);
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GA_G->setVisibility(G->getVisibility());
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G->replaceAllUsesWith(GA_G);
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G->eraseFromParent();
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++NumFunctionsMerged;
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return true;
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}
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DOUT << "Failed on " << F->getName() << " and " << G->getName() << "\n";
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++NumMergeFails;
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return false;
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}
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static bool hasAddressTaken(User *U) {
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for (User::use_iterator I = U->use_begin(), E = U->use_end(); I != E; ++I) {
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User *Use = *I;
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// 'call (bitcast @F to ...)' happens a lot.
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while (isa<ConstantExpr>(Use) && Use->hasOneUse()) {
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Use = *Use->use_begin();
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}
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if (isa<ConstantExpr>(Use)) {
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if (hasAddressTaken(Use))
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return true;
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}
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if (!isa<CallInst>(Use) && !isa<InvokeInst>(Use))
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return true;
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// Make sure we aren't passing U as a parameter to call instead of the
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// callee.
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if (CallSite(cast<Instruction>(Use)).hasArgument(U))
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return true;
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}
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return false;
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}
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bool MergeFunctions::runOnModule(Module &M) {
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bool Changed = false;
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std::map<unsigned long, std::vector<Function *> > FnMap;
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for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
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if (F->isDeclaration() || F->isIntrinsic())
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continue;
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if (!F->hasLocalLinkage() && !F->hasExternalLinkage() &&
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!F->hasWeakLinkage())
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continue;
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if (hasAddressTaken(F))
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continue;
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FnMap[hash(F)].push_back(F);
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}
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// TODO: instead of running in a loop, we could also fold functions in callgraph
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// order. Constructing the CFG probably isn't cheaper than just running in a loop.
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bool LocalChanged;
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do {
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LocalChanged = false;
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for (std::map<unsigned long, std::vector<Function *> >::iterator
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I = FnMap.begin(), E = FnMap.end(); I != E; ++I) {
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DOUT << "size: " << FnMap.size() << "\n";
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std::vector<Function *> &FnVec = I->second;
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DOUT << "hash (" << I->first << "): " << FnVec.size() << "\n";
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for (int i = 0, e = FnVec.size(); i != e; ++i) {
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for (int j = i + 1; j != e; ++j) {
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bool isEqual = equals(FnVec[i], FnVec[j]);
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DOUT << " " << FnVec[i]->getName()
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<< (isEqual ? " == " : " != ")
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<< FnVec[j]->getName() << "\n";
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if (isEqual) {
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if (fold(FnVec, i, j)) {
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LocalChanged = true;
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FnVec.erase(FnVec.begin() + j);
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--j, --e;
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}
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}
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}
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}
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}
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Changed |= LocalChanged;
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} while (LocalChanged);
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return Changed;
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}
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