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/AssumptionTracker.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))
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(const Loop *L, AssumptionTracker *AT,
70 SmallPtrSetImpl<const Value*> &EphValues) {
71 SmallVector<const Value *, 16> WorkSet;
73 for (auto &I : AT->assumptions(L->getHeader()->getParent())) {
74 // Filter out call sites outside of the loop so we don't to a function's
75 // worth of work for each of its loops (and, in the common case, ephemeral
76 // values in the loop are likely due to @llvm.assume calls in the loop).
77 if (!L->contains(I->getParent()))
83 completeEphemeralValues(WorkSet, EphValues);
86 void CodeMetrics::collectEphemeralValues(const Function *F, AssumptionTracker *AT,
87 SmallPtrSetImpl<const Value*> &EphValues) {
88 SmallVector<const Value *, 16> WorkSet;
90 for (auto &I : AT->assumptions(const_cast<Function*>(F)))
93 completeEphemeralValues(WorkSet, EphValues);
96 /// analyzeBasicBlock - Fill in the current structure with information gleaned
97 /// from the specified block.
98 void CodeMetrics::analyzeBasicBlock(const BasicBlock *BB,
99 const TargetTransformInfo &TTI,
100 SmallPtrSetImpl<const Value*> &EphValues) {
102 unsigned NumInstsBeforeThisBB = NumInsts;
103 for (BasicBlock::const_iterator II = BB->begin(), E = BB->end();
105 // Skip ephemeral values.
106 if (EphValues.count(II))
109 // Special handling for calls.
110 if (isa<CallInst>(II) || isa<InvokeInst>(II)) {
111 ImmutableCallSite CS(cast<Instruction>(II));
113 if (const Function *F = CS.getCalledFunction()) {
114 // If a function is both internal and has a single use, then it is
115 // extremely likely to get inlined in the future (it was probably
116 // exposed by an interleaved devirtualization pass).
117 if (!CS.isNoInline() && F->hasInternalLinkage() && F->hasOneUse())
118 ++NumInlineCandidates;
120 // If this call is to function itself, then the function is recursive.
121 // Inlining it into other functions is a bad idea, because this is
122 // basically just a form of loop peeling, and our metrics aren't useful
124 if (F == BB->getParent())
127 if (TTI.isLoweredToCall(F))
130 // We don't want inline asm to count as a call - that would prevent loop
131 // unrolling. The argument setup cost is still real, though.
132 if (!isa<InlineAsm>(CS.getCalledValue()))
137 if (const AllocaInst *AI = dyn_cast<AllocaInst>(II)) {
138 if (!AI->isStaticAlloca())
139 this->usesDynamicAlloca = true;
142 if (isa<ExtractElementInst>(II) || II->getType()->isVectorTy())
145 if (const CallInst *CI = dyn_cast<CallInst>(II))
146 if (CI->cannotDuplicate())
147 notDuplicatable = true;
149 if (const InvokeInst *InvI = dyn_cast<InvokeInst>(II))
150 if (InvI->cannotDuplicate())
151 notDuplicatable = true;
153 NumInsts += TTI.getUserCost(&*II);
156 if (isa<ReturnInst>(BB->getTerminator()))
159 // We never want to inline functions that contain an indirectbr. This is
160 // incorrect because all the blockaddress's (in static global initializers
161 // for example) would be referring to the original function, and this indirect
162 // jump would jump from the inlined copy of the function into the original
163 // function which is extremely undefined behavior.
164 // FIXME: This logic isn't really right; we can safely inline functions
165 // with indirectbr's as long as no other function or global references the
166 // blockaddress of a block within the current function. And as a QOI issue,
167 // if someone is using a blockaddress without an indirectbr, and that
168 // reference somehow ends up in another function or global, we probably
169 // don't want to inline this function.
170 notDuplicatable |= isa<IndirectBrInst>(BB->getTerminator());
172 // Remember NumInsts for this BB.
173 NumBBInsts[BB] = NumInsts - NumInstsBeforeThisBB;