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.pop_back_val();
41 if (!Visited.insert(V))
44 // If all uses of this value are ephemeral, then so is this value.
45 bool FoundNEUse = false;
46 for (const User *I : V->users())
47 if (!EphValues.count(I)) {
56 DEBUG(dbgs() << "Ephemeral Value: " << *V << "\n");
58 if (const User *U = dyn_cast<User>(V))
59 for (const Value *J : U->operands()) {
60 if (isSafeToSpeculativelyExecute(J))
66 // Find all ephemeral values.
67 void CodeMetrics::collectEphemeralValues(const Loop *L, AssumptionTracker *AT,
68 SmallPtrSetImpl<const Value*> &EphValues) {
69 SmallVector<const Value *, 16> WorkSet;
71 for (auto &I : AT->assumptions(L->getHeader()->getParent())) {
72 // Filter out call sites outside of the loop so we don't to a function's
73 // worth of work for each of its loops (and, in the common case, ephemeral
74 // values in the loop are likely due to @llvm.assume calls in the loop).
75 if (!L->contains(I->getParent()))
81 completeEphemeralValues(WorkSet, EphValues);
84 void CodeMetrics::collectEphemeralValues(const Function *F, AssumptionTracker *AT,
85 SmallPtrSetImpl<const Value*> &EphValues) {
86 SmallVector<const Value *, 16> WorkSet;
88 for (auto &I : AT->assumptions(const_cast<Function*>(F)))
91 completeEphemeralValues(WorkSet, EphValues);
94 /// analyzeBasicBlock - Fill in the current structure with information gleaned
95 /// from the specified block.
96 void CodeMetrics::analyzeBasicBlock(const BasicBlock *BB,
97 const TargetTransformInfo &TTI,
98 SmallPtrSetImpl<const Value*> &EphValues) {
100 unsigned NumInstsBeforeThisBB = NumInsts;
101 for (BasicBlock::const_iterator II = BB->begin(), E = BB->end();
103 // Skip ephemeral values.
104 if (EphValues.count(II))
107 // Special handling for calls.
108 if (isa<CallInst>(II) || isa<InvokeInst>(II)) {
109 ImmutableCallSite CS(cast<Instruction>(II));
111 if (const Function *F = CS.getCalledFunction()) {
112 // If a function is both internal and has a single use, then it is
113 // extremely likely to get inlined in the future (it was probably
114 // exposed by an interleaved devirtualization pass).
115 if (!CS.isNoInline() && F->hasInternalLinkage() && F->hasOneUse())
116 ++NumInlineCandidates;
118 // If this call is to function itself, then the function is recursive.
119 // Inlining it into other functions is a bad idea, because this is
120 // basically just a form of loop peeling, and our metrics aren't useful
122 if (F == BB->getParent())
125 if (TTI.isLoweredToCall(F))
128 // We don't want inline asm to count as a call - that would prevent loop
129 // unrolling. The argument setup cost is still real, though.
130 if (!isa<InlineAsm>(CS.getCalledValue()))
135 if (const AllocaInst *AI = dyn_cast<AllocaInst>(II)) {
136 if (!AI->isStaticAlloca())
137 this->usesDynamicAlloca = true;
140 if (isa<ExtractElementInst>(II) || II->getType()->isVectorTy())
143 if (const CallInst *CI = dyn_cast<CallInst>(II))
144 if (CI->cannotDuplicate())
145 notDuplicatable = true;
147 if (const InvokeInst *InvI = dyn_cast<InvokeInst>(II))
148 if (InvI->cannotDuplicate())
149 notDuplicatable = true;
151 NumInsts += TTI.getUserCost(&*II);
154 if (isa<ReturnInst>(BB->getTerminator()))
157 // We never want to inline functions that contain an indirectbr. This is
158 // incorrect because all the blockaddress's (in static global initializers
159 // for example) would be referring to the original function, and this indirect
160 // jump would jump from the inlined copy of the function into the original
161 // function which is extremely undefined behavior.
162 // FIXME: This logic isn't really right; we can safely inline functions
163 // with indirectbr's as long as no other function or global references the
164 // blockaddress of a block within the current function. And as a QOI issue,
165 // if someone is using a blockaddress without an indirectbr, and that
166 // reference somehow ends up in another function or global, we probably
167 // don't want to inline this function.
168 notDuplicatable |= isa<IndirectBrInst>(BB->getTerminator());
170 // Remember NumInsts for this BB.
171 NumBBInsts[BB] = NumInsts - NumInstsBeforeThisBB;