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//===- CodeMetrics.cpp - Code cost measurements ---------------------------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file implements code cost measurement utilities.
#include "llvm/Analysis/CodeMetrics.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Function.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/InstructionCost.h"
#define DEBUG_TYPE "code-metrics"
using namespace llvm;
static void
appendSpeculatableOperands(const Value *V,
SmallPtrSetImpl<const Value *> &Visited,
SmallVectorImpl<const Value *> &Worklist) {
const User *U = dyn_cast<User>(V);
if (!U)
for (const Value *Operand : U->operands())
if (Visited.insert(Operand).second)
if (const auto *I = dyn_cast<Instruction>(Operand))
if (!I->mayHaveSideEffects() && !I->isTerminator())
static void completeEphemeralValues(SmallPtrSetImpl<const Value *> &Visited,
SmallVectorImpl<const Value *> &Worklist,
SmallPtrSetImpl<const Value *> &EphValues) {
// Note: We don't speculate PHIs here, so we'll miss instruction chains kept
// alive only by ephemeral values.
// Walk the worklist using an index but without caching the size so we can
// append more entries as we process the worklist. This forms a queue without
// quadratic behavior by just leaving processed nodes at the head of the
// worklist forever.
for (int i = 0; i < (int)Worklist.size(); ++i) {
const Value *V = Worklist[i];
assert(Visited.count(V) &&
"Failed to add a worklist entry to our visited set!");
// If all uses of this value are ephemeral, then so is this value.
if (!all_of(V->users(), [&](const User *U) { return EphValues.count(U); }))
LLVM_DEBUG(dbgs() << "Ephemeral Value: " << *V << "\n");
// Append any more operands to consider.
appendSpeculatableOperands(V, Visited, Worklist);
// Find all ephemeral values.
void CodeMetrics::collectEphemeralValues(
const Loop *L, AssumptionCache *AC,
SmallPtrSetImpl<const Value *> &EphValues) {
SmallPtrSet<const Value *, 32> Visited;
SmallVector<const Value *, 16> Worklist;
for (auto &AssumeVH : AC->assumptions()) {
if (!AssumeVH)
Instruction *I = cast<Instruction>(AssumeVH);
// Filter out call sites outside of the loop so we don't do a function's
// worth of work for each of its loops (and, in the common case, ephemeral
// values in the loop are likely due to @llvm.assume calls in the loop).
if (!L->contains(I->getParent()))
if (EphValues.insert(I).second)
appendSpeculatableOperands(I, Visited, Worklist);
completeEphemeralValues(Visited, Worklist, EphValues);
void CodeMetrics::collectEphemeralValues(
const Function *F, AssumptionCache *AC,
SmallPtrSetImpl<const Value *> &EphValues) {
SmallPtrSet<const Value *, 32> Visited;
SmallVector<const Value *, 16> Worklist;
for (auto &AssumeVH : AC->assumptions()) {
if (!AssumeVH)
Instruction *I = cast<Instruction>(AssumeVH);
assert(I->getParent()->getParent() == F &&
"Found assumption for the wrong function!");
if (EphValues.insert(I).second)
appendSpeculatableOperands(I, Visited, Worklist);
completeEphemeralValues(Visited, Worklist, EphValues);
/// Fill in the current structure with information gleaned from the specified
/// block.
void CodeMetrics::analyzeBasicBlock(
const BasicBlock *BB, const TargetTransformInfo &TTI,
const SmallPtrSetImpl<const Value *> &EphValues, bool PrepareForLTO) {
// Use a proxy variable for NumInsts of type InstructionCost, so that it can
// use InstructionCost's arithmetic properties such as saturation when this
// feature is added to InstructionCost.
// When storing the value back to NumInsts, we can assume all costs are Valid
// because the IR should not contain any nodes that cannot be costed. If that
// happens the cost-model is broken.
InstructionCost NumInstsProxy = NumInsts;
InstructionCost NumInstsBeforeThisBB = NumInsts;
for (const Instruction &I : *BB) {
// Skip ephemeral values.
if (EphValues.count(&I))
// Special handling for calls.
if (const auto *Call = dyn_cast<CallBase>(&I)) {
if (const Function *F = Call->getCalledFunction()) {
bool IsLoweredToCall = TTI.isLoweredToCall(F);
// If a function is both internal and has a single use, then it is
// extremely likely to get inlined in the future (it was probably
// exposed by an interleaved devirtualization pass).
// When preparing for LTO, liberally consider calls as inline
// candidates.
if (!Call->isNoInline() && IsLoweredToCall &&
((F->hasInternalLinkage() && F->hasOneUse()) || PrepareForLTO)) {
// If this call is to function itself, then the function is recursive.
// Inlining it into other functions is a bad idea, because this is
// basically just a form of loop peeling, and our metrics aren't useful
// for that case.
if (F == BB->getParent())
isRecursive = true;
if (IsLoweredToCall)
} else {
// We don't want inline asm to count as a call - that would prevent loop
// unrolling. The argument setup cost is still real, though.
if (!Call->isInlineAsm())
if (const AllocaInst *AI = dyn_cast<AllocaInst>(&I)) {
if (!AI->isStaticAlloca())
this->usesDynamicAlloca = true;
if (isa<ExtractElementInst>(I) || I.getType()->isVectorTy())
if (I.getType()->isTokenTy() && I.isUsedOutsideOfBlock(BB))
notDuplicatable = true;
if (const CallInst *CI = dyn_cast<CallInst>(&I)) {
if (CI->cannotDuplicate())
notDuplicatable = true;
if (CI->isConvergent())
convergent = true;
if (const InvokeInst *InvI = dyn_cast<InvokeInst>(&I))
if (InvI->cannotDuplicate())
notDuplicatable = true;
NumInstsProxy += TTI.getUserCost(&I, TargetTransformInfo::TCK_CodeSize);
NumInsts = *NumInstsProxy.getValue();
if (isa<ReturnInst>(BB->getTerminator()))
// We never want to inline functions that contain an indirectbr. This is
// incorrect because all the blockaddress's (in static global initializers
// for example) would be referring to the original function, and this indirect
// jump would jump from the inlined copy of the function into the original
// function which is extremely undefined behavior.
// FIXME: This logic isn't really right; we can safely inline functions
// with indirectbr's as long as no other function or global references the
// blockaddress of a block within the current function. And as a QOI issue,
// if someone is using a blockaddress without an indirectbr, and that
// reference somehow ends up in another function or global, we probably
// don't want to inline this function.
notDuplicatable |= isa<IndirectBrInst>(BB->getTerminator());
// Remember NumInsts for this BB.
InstructionCost NumInstsThisBB = NumInstsProxy - NumInstsBeforeThisBB;
NumBBInsts[BB] = *NumInstsThisBB.getValue();