1 //===- CodeMetrics.cpp - Code cost measurements ---------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements code cost measurement utilities.
12 //===----------------------------------------------------------------------===//
14 #include "llvm/Analysis/AssumptionCache.h"
15 #include "llvm/Analysis/CodeMetrics.h"
16 #include "llvm/Analysis/LoopInfo.h"
17 #include "llvm/Analysis/TargetTransformInfo.h"
18 #include "llvm/Analysis/ValueTracking.h"
19 #include "llvm/IR/CallSite.h"
20 #include "llvm/IR/DataLayout.h"
21 #include "llvm/IR/Function.h"
22 #include "llvm/IR/IntrinsicInst.h"
23 #include "llvm/Support/Debug.h"
25 #define DEBUG_TYPE "code-metrics"
29 static void completeEphemeralValues(SmallVector<const Value *, 16> &WorkSet,
30 SmallPtrSetImpl<const Value*> &EphValues) {
31 SmallPtrSet<const Value *, 32> Visited;
33 // Make sure that all of the items in WorkSet are in our EphValues set.
34 EphValues.insert(WorkSet.begin(), WorkSet.end());
36 // Note: We don't speculate PHIs here, so we'll miss instruction chains kept
37 // alive only by ephemeral values.
39 while (!WorkSet.empty()) {
40 const Value *V = WorkSet.front();
41 WorkSet.erase(WorkSet.begin());
43 if (!Visited.insert(V).second)
46 // If all uses of this value are ephemeral, then so is this value.
47 bool FoundNEUse = false;
48 for (const User *I : V->users())
49 if (!EphValues.count(I)) {
58 DEBUG(dbgs() << "Ephemeral Value: " << *V << "\n");
60 if (const User *U = dyn_cast<User>(V))
61 for (const Value *J : U->operands()) {
62 if (isSafeToSpeculativelyExecute(J))
68 // Find all ephemeral values.
69 void CodeMetrics::collectEphemeralValues(
70 const Loop *L, AssumptionCache *AC,
71 SmallPtrSetImpl<const Value *> &EphValues) {
72 SmallVector<const Value *, 16> WorkSet;
74 for (auto &AssumeVH : AC->assumptions()) {
77 Instruction *I = cast<Instruction>(AssumeVH);
79 // Filter out call sites outside of the loop so we don't to a function's
80 // worth of work for each of its loops (and, in the common case, ephemeral
81 // values in the loop are likely due to @llvm.assume calls in the loop).
82 if (!L->contains(I->getParent()))
88 completeEphemeralValues(WorkSet, EphValues);
91 void CodeMetrics::collectEphemeralValues(
92 const Function *F, AssumptionCache *AC,
93 SmallPtrSetImpl<const Value *> &EphValues) {
94 SmallVector<const Value *, 16> WorkSet;
96 for (auto &AssumeVH : AC->assumptions()) {
99 Instruction *I = cast<Instruction>(AssumeVH);
100 assert(I->getParent()->getParent() == F &&
101 "Found assumption for the wrong function!");
102 WorkSet.push_back(I);
105 completeEphemeralValues(WorkSet, EphValues);
108 /// analyzeBasicBlock - Fill in the current structure with information gleaned
109 /// from the specified block.
110 void CodeMetrics::analyzeBasicBlock(const BasicBlock *BB,
111 const TargetTransformInfo &TTI,
112 SmallPtrSetImpl<const Value*> &EphValues) {
114 unsigned NumInstsBeforeThisBB = NumInsts;
115 for (BasicBlock::const_iterator II = BB->begin(), E = BB->end();
117 // Skip ephemeral values.
118 if (EphValues.count(II))
121 // Special handling for calls.
122 if (isa<CallInst>(II) || isa<InvokeInst>(II)) {
123 ImmutableCallSite CS(cast<Instruction>(II));
125 if (const Function *F = CS.getCalledFunction()) {
126 // If a function is both internal and has a single use, then it is
127 // extremely likely to get inlined in the future (it was probably
128 // exposed by an interleaved devirtualization pass).
129 if (!CS.isNoInline() && F->hasInternalLinkage() && F->hasOneUse())
130 ++NumInlineCandidates;
132 // If this call is to function itself, then the function is recursive.
133 // Inlining it into other functions is a bad idea, because this is
134 // basically just a form of loop peeling, and our metrics aren't useful
136 if (F == BB->getParent())
139 if (TTI.isLoweredToCall(F))
142 // We don't want inline asm to count as a call - that would prevent loop
143 // unrolling. The argument setup cost is still real, though.
144 if (!isa<InlineAsm>(CS.getCalledValue()))
149 if (const AllocaInst *AI = dyn_cast<AllocaInst>(II)) {
150 if (!AI->isStaticAlloca())
151 this->usesDynamicAlloca = true;
154 if (isa<ExtractElementInst>(II) || II->getType()->isVectorTy())
157 if (const CallInst *CI = dyn_cast<CallInst>(II))
158 if (CI->cannotDuplicate())
159 notDuplicatable = true;
161 if (const InvokeInst *InvI = dyn_cast<InvokeInst>(II))
162 if (InvI->cannotDuplicate())
163 notDuplicatable = true;
165 NumInsts += TTI.getUserCost(&*II);
168 if (isa<ReturnInst>(BB->getTerminator()))
171 // We never want to inline functions that contain an indirectbr. This is
172 // incorrect because all the blockaddress's (in static global initializers
173 // for example) would be referring to the original function, and this indirect
174 // jump would jump from the inlined copy of the function into the original
175 // function which is extremely undefined behavior.
176 // FIXME: This logic isn't really right; we can safely inline functions
177 // with indirectbr's as long as no other function or global references the
178 // blockaddress of a block within the current function. And as a QOI issue,
179 // if someone is using a blockaddress without an indirectbr, and that
180 // reference somehow ends up in another function or global, we probably
181 // don't want to inline this function.
182 notDuplicatable |= isa<IndirectBrInst>(BB->getTerminator());
184 // Remember NumInsts for this BB.
185 NumBBInsts[BB] = NumInsts - NumInstsBeforeThisBB;