200 lines
7.0 KiB
C++
200 lines
7.0 KiB
C++
//===- CodeMetrics.cpp - Code cost measurements ---------------------------===//
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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 file implements code cost measurement utilities.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/CodeMetrics.h"
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#include "llvm/Analysis/AssumptionCache.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Analysis/TargetTransformInfo.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/IR/CallSite.h"
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#include "llvm/IR/DataLayout.h"
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#include "llvm/IR/Function.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#define DEBUG_TYPE "code-metrics"
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using namespace llvm;
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static void
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appendSpeculatableOperands(const Value *V,
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SmallPtrSetImpl<const Value *> &Visited,
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SmallVectorImpl<const Value *> &Worklist) {
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const User *U = dyn_cast<User>(V);
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if (!U)
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return;
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for (const Value *Operand : U->operands())
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if (Visited.insert(Operand).second)
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if (isSafeToSpeculativelyExecute(Operand))
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Worklist.push_back(Operand);
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}
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static void completeEphemeralValues(SmallPtrSetImpl<const Value *> &Visited,
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SmallVectorImpl<const Value *> &Worklist,
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SmallPtrSetImpl<const Value *> &EphValues) {
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// Note: We don't speculate PHIs here, so we'll miss instruction chains kept
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// alive only by ephemeral values.
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// Walk the worklist using an index but without caching the size so we can
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// append more entries as we process the worklist. This forms a queue without
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// quadratic behavior by just leaving processed nodes at the head of the
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// worklist forever.
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for (int i = 0; i < (int)Worklist.size(); ++i) {
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const Value *V = Worklist[i];
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assert(Visited.count(V) &&
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"Failed to add a worklist entry to our visited set!");
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// If all uses of this value are ephemeral, then so is this value.
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if (!all_of(V->users(), [&](const User *U) { return EphValues.count(U); }))
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continue;
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EphValues.insert(V);
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DEBUG(dbgs() << "Ephemeral Value: " << *V << "\n");
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// Append any more operands to consider.
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appendSpeculatableOperands(V, Visited, Worklist);
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}
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}
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// Find all ephemeral values.
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void CodeMetrics::collectEphemeralValues(
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const Loop *L, AssumptionCache *AC,
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SmallPtrSetImpl<const Value *> &EphValues) {
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SmallPtrSet<const Value *, 32> Visited;
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SmallVector<const Value *, 16> Worklist;
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for (auto &AssumeVH : AC->assumptions()) {
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if (!AssumeVH)
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continue;
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Instruction *I = cast<Instruction>(AssumeVH);
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// Filter out call sites outside of the loop so we don't do a function's
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// worth of work for each of its loops (and, in the common case, ephemeral
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// values in the loop are likely due to @llvm.assume calls in the loop).
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if (!L->contains(I->getParent()))
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continue;
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if (EphValues.insert(I).second)
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appendSpeculatableOperands(I, Visited, Worklist);
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}
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completeEphemeralValues(Visited, Worklist, EphValues);
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}
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void CodeMetrics::collectEphemeralValues(
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const Function *F, AssumptionCache *AC,
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SmallPtrSetImpl<const Value *> &EphValues) {
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SmallPtrSet<const Value *, 32> Visited;
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SmallVector<const Value *, 16> Worklist;
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for (auto &AssumeVH : AC->assumptions()) {
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if (!AssumeVH)
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continue;
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Instruction *I = cast<Instruction>(AssumeVH);
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assert(I->getParent()->getParent() == F &&
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"Found assumption for the wrong function!");
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if (EphValues.insert(I).second)
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appendSpeculatableOperands(I, Visited, Worklist);
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}
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completeEphemeralValues(Visited, Worklist, EphValues);
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}
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/// Fill in the current structure with information gleaned from the specified
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/// block.
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void CodeMetrics::analyzeBasicBlock(const BasicBlock *BB,
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const TargetTransformInfo &TTI,
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const SmallPtrSetImpl<const Value*> &EphValues) {
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++NumBlocks;
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unsigned NumInstsBeforeThisBB = NumInsts;
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for (const Instruction &I : *BB) {
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// Skip ephemeral values.
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if (EphValues.count(&I))
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continue;
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// Special handling for calls.
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if (isa<CallInst>(I) || isa<InvokeInst>(I)) {
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ImmutableCallSite CS(&I);
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if (const Function *F = CS.getCalledFunction()) {
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// If a function is both internal and has a single use, then it is
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// extremely likely to get inlined in the future (it was probably
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// exposed by an interleaved devirtualization pass).
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if (!CS.isNoInline() && F->hasInternalLinkage() && F->hasOneUse())
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++NumInlineCandidates;
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// If this call is to function itself, then the function is recursive.
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// Inlining it into other functions is a bad idea, because this is
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// basically just a form of loop peeling, and our metrics aren't useful
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// for that case.
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if (F == BB->getParent())
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isRecursive = true;
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if (TTI.isLoweredToCall(F))
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++NumCalls;
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} else {
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// We don't want inline asm to count as a call - that would prevent loop
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// unrolling. The argument setup cost is still real, though.
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if (!isa<InlineAsm>(CS.getCalledValue()))
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++NumCalls;
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}
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}
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if (const AllocaInst *AI = dyn_cast<AllocaInst>(&I)) {
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if (!AI->isStaticAlloca())
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this->usesDynamicAlloca = true;
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}
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if (isa<ExtractElementInst>(I) || I.getType()->isVectorTy())
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++NumVectorInsts;
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if (I.getType()->isTokenTy() && I.isUsedOutsideOfBlock(BB))
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notDuplicatable = true;
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if (const CallInst *CI = dyn_cast<CallInst>(&I)) {
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if (CI->cannotDuplicate())
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notDuplicatable = true;
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if (CI->isConvergent())
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convergent = true;
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}
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if (const InvokeInst *InvI = dyn_cast<InvokeInst>(&I))
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if (InvI->cannotDuplicate())
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notDuplicatable = true;
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NumInsts += TTI.getUserCost(&I);
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}
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if (isa<ReturnInst>(BB->getTerminator()))
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++NumRets;
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// We never want to inline functions that contain an indirectbr. This is
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// incorrect because all the blockaddress's (in static global initializers
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// for example) would be referring to the original function, and this indirect
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// jump would jump from the inlined copy of the function into the original
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// function which is extremely undefined behavior.
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// FIXME: This logic isn't really right; we can safely inline functions
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// with indirectbr's as long as no other function or global references the
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// blockaddress of a block within the current function. And as a QOI issue,
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// if someone is using a blockaddress without an indirectbr, and that
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// reference somehow ends up in another function or global, we probably
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// don't want to inline this function.
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notDuplicatable |= isa<IndirectBrInst>(BB->getTerminator());
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// Remember NumInsts for this BB.
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NumBBInsts[BB] = NumInsts - NumInstsBeforeThisBB;
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}
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