1 //===- CodeMetrics.cpp - Code cost measurements ---------------------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements code cost measurement utilities.
11 //
12 //===----------------------------------------------------------------------===//
13
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"
24 #include "llvm/Support/raw_ostream.h"
25
26 #define DEBUG_TYPE "code-metrics"
27
28 using namespace llvm;
29
completeEphemeralValues(SmallVector<const Value *,16> & WorkSet,SmallPtrSetImpl<const Value * > & EphValues)30 static void completeEphemeralValues(SmallVector<const Value *, 16> &WorkSet,
31 SmallPtrSetImpl<const Value*> &EphValues) {
32 SmallPtrSet<const Value *, 32> Visited;
33
34 // Make sure that all of the items in WorkSet are in our EphValues set.
35 EphValues.insert(WorkSet.begin(), WorkSet.end());
36
37 // Note: We don't speculate PHIs here, so we'll miss instruction chains kept
38 // alive only by ephemeral values.
39
40 while (!WorkSet.empty()) {
41 const Value *V = WorkSet.front();
42 WorkSet.erase(WorkSet.begin());
43
44 if (!Visited.insert(V).second)
45 continue;
46
47 // If all uses of this value are ephemeral, then so is this value.
48 if (!std::all_of(V->user_begin(), V->user_end(),
49 [&](const User *U) { return EphValues.count(U); }))
50 continue;
51
52 EphValues.insert(V);
53 DEBUG(dbgs() << "Ephemeral Value: " << *V << "\n");
54
55 if (const User *U = dyn_cast<User>(V))
56 for (const Value *J : U->operands()) {
57 if (isSafeToSpeculativelyExecute(J))
58 WorkSet.push_back(J);
59 }
60 }
61 }
62
63 // Find all ephemeral values.
collectEphemeralValues(const Loop * L,AssumptionCache * AC,SmallPtrSetImpl<const Value * > & EphValues)64 void CodeMetrics::collectEphemeralValues(
65 const Loop *L, AssumptionCache *AC,
66 SmallPtrSetImpl<const Value *> &EphValues) {
67 SmallVector<const Value *, 16> WorkSet;
68
69 for (auto &AssumeVH : AC->assumptions()) {
70 if (!AssumeVH)
71 continue;
72 Instruction *I = cast<Instruction>(AssumeVH);
73
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()))
78 continue;
79
80 WorkSet.push_back(I);
81 }
82
83 completeEphemeralValues(WorkSet, EphValues);
84 }
85
collectEphemeralValues(const Function * F,AssumptionCache * AC,SmallPtrSetImpl<const Value * > & EphValues)86 void CodeMetrics::collectEphemeralValues(
87 const Function *F, AssumptionCache *AC,
88 SmallPtrSetImpl<const Value *> &EphValues) {
89 SmallVector<const Value *, 16> WorkSet;
90
91 for (auto &AssumeVH : AC->assumptions()) {
92 if (!AssumeVH)
93 continue;
94 Instruction *I = cast<Instruction>(AssumeVH);
95 assert(I->getParent()->getParent() == F &&
96 "Found assumption for the wrong function!");
97 WorkSet.push_back(I);
98 }
99
100 completeEphemeralValues(WorkSet, EphValues);
101 }
102
103 /// analyzeBasicBlock - Fill in the current structure with information gleaned
104 /// from the specified block.
analyzeBasicBlock(const BasicBlock * BB,const TargetTransformInfo & TTI,SmallPtrSetImpl<const Value * > & EphValues)105 void CodeMetrics::analyzeBasicBlock(const BasicBlock *BB,
106 const TargetTransformInfo &TTI,
107 SmallPtrSetImpl<const Value*> &EphValues) {
108 ++NumBlocks;
109 unsigned NumInstsBeforeThisBB = NumInsts;
110 for (BasicBlock::const_iterator II = BB->begin(), E = BB->end();
111 II != E; ++II) {
112 // Skip ephemeral values.
113 if (EphValues.count(&*II))
114 continue;
115
116 // Special handling for calls.
117 if (isa<CallInst>(II) || isa<InvokeInst>(II)) {
118 ImmutableCallSite CS(cast<Instruction>(II));
119
120 if (const Function *F = CS.getCalledFunction()) {
121 // If a function is both internal and has a single use, then it is
122 // extremely likely to get inlined in the future (it was probably
123 // exposed by an interleaved devirtualization pass).
124 if (!CS.isNoInline() && F->hasInternalLinkage() && F->hasOneUse())
125 ++NumInlineCandidates;
126
127 // If this call is to function itself, then the function is recursive.
128 // Inlining it into other functions is a bad idea, because this is
129 // basically just a form of loop peeling, and our metrics aren't useful
130 // for that case.
131 if (F == BB->getParent())
132 isRecursive = true;
133
134 if (TTI.isLoweredToCall(F))
135 ++NumCalls;
136 } else {
137 // We don't want inline asm to count as a call - that would prevent loop
138 // unrolling. The argument setup cost is still real, though.
139 if (!isa<InlineAsm>(CS.getCalledValue()))
140 ++NumCalls;
141 }
142 }
143
144 if (const AllocaInst *AI = dyn_cast<AllocaInst>(II)) {
145 if (!AI->isStaticAlloca())
146 this->usesDynamicAlloca = true;
147 }
148
149 if (isa<ExtractElementInst>(II) || II->getType()->isVectorTy())
150 ++NumVectorInsts;
151
152 if (II->getType()->isTokenTy() && II->isUsedOutsideOfBlock(BB))
153 notDuplicatable = true;
154
155 if (const CallInst *CI = dyn_cast<CallInst>(II))
156 if (CI->cannotDuplicate())
157 notDuplicatable = true;
158
159 if (const InvokeInst *InvI = dyn_cast<InvokeInst>(II))
160 if (InvI->cannotDuplicate())
161 notDuplicatable = true;
162
163 NumInsts += TTI.getUserCost(&*II);
164 }
165
166 if (isa<ReturnInst>(BB->getTerminator()))
167 ++NumRets;
168
169 // We never want to inline functions that contain an indirectbr. This is
170 // incorrect because all the blockaddress's (in static global initializers
171 // for example) would be referring to the original function, and this indirect
172 // jump would jump from the inlined copy of the function into the original
173 // function which is extremely undefined behavior.
174 // FIXME: This logic isn't really right; we can safely inline functions
175 // with indirectbr's as long as no other function or global references the
176 // blockaddress of a block within the current function. And as a QOI issue,
177 // if someone is using a blockaddress without an indirectbr, and that
178 // reference somehow ends up in another function or global, we probably
179 // don't want to inline this function.
180 notDuplicatable |= isa<IndirectBrInst>(BB->getTerminator());
181
182 // Remember NumInsts for this BB.
183 NumBBInsts[BB] = NumInsts - NumInstsBeforeThisBB;
184 }
185