1//===- CodeMetrics.cpp - Code cost measurements ---------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file implements code cost measurement utilities.
10//
11//===----------------------------------------------------------------------===//
12
13#include "llvm/Analysis/CodeMetrics.h"
14#include "llvm/ADT/SmallPtrSet.h"
15#include "llvm/Analysis/AssumptionCache.h"
16#include "llvm/Analysis/LoopInfo.h"
17#include "llvm/Analysis/TargetTransformInfo.h"
18#include "llvm/IR/Function.h"
19#include "llvm/Support/Debug.h"
20#include "llvm/Support/InstructionCost.h"
21
22#define DEBUG_TYPE "code-metrics"
23
24using namespace llvm;
25
26static void
27appendSpeculatableOperands(const Value *V,
28 SmallPtrSetImpl<const Value *> &Visited,
29 SmallVectorImpl<const Value *> &Worklist) {
30 const User *U = dyn_cast<User>(Val: V);
31 if (!U)
32 return;
33
34 for (const Value *Operand : U->operands())
35 if (Visited.insert(Ptr: Operand).second)
36 if (const auto *I = dyn_cast<Instruction>(Val: Operand))
37 if (!I->mayHaveSideEffects() && !I->isTerminator())
38 Worklist.push_back(Elt: I);
39}
40
41static void completeEphemeralValues(SmallPtrSetImpl<const Value *> &Visited,
42 SmallVectorImpl<const Value *> &Worklist,
43 SmallPtrSetImpl<const Value *> &EphValues) {
44 // Note: We don't speculate PHIs here, so we'll miss instruction chains kept
45 // alive only by ephemeral values.
46
47 // Walk the worklist using an index but without caching the size so we can
48 // append more entries as we process the worklist. This forms a queue without
49 // quadratic behavior by just leaving processed nodes at the head of the
50 // worklist forever.
51 for (int i = 0; i < (int)Worklist.size(); ++i) {
52 const Value *V = Worklist[i];
53
54 assert(Visited.count(V) &&
55 "Failed to add a worklist entry to our visited set!");
56
57 // If all uses of this value are ephemeral, then so is this value.
58 if (!all_of(Range: V->users(), P: [&](const User *U) { return EphValues.count(Ptr: U); }))
59 continue;
60
61 EphValues.insert(Ptr: V);
62 LLVM_DEBUG(dbgs() << "Ephemeral Value: " << *V << "\n");
63
64 // Append any more operands to consider.
65 appendSpeculatableOperands(V, Visited, Worklist);
66 }
67}
68
69// Find all ephemeral values.
70void CodeMetrics::collectEphemeralValues(
71 const Loop *L, AssumptionCache *AC,
72 SmallPtrSetImpl<const Value *> &EphValues) {
73 SmallPtrSet<const Value *, 32> Visited;
74 SmallVector<const Value *, 16> Worklist;
75
76 for (auto &AssumeVH : AC->assumptions()) {
77 if (!AssumeVH)
78 continue;
79 Instruction *I = cast<Instruction>(Val&: AssumeVH);
80
81 // Filter out call sites outside of the loop so we don't do a function's
82 // worth of work for each of its loops (and, in the common case, ephemeral
83 // values in the loop are likely due to @llvm.assume calls in the loop).
84 if (!L->contains(BB: I->getParent()))
85 continue;
86
87 if (EphValues.insert(Ptr: I).second)
88 appendSpeculatableOperands(V: I, Visited, Worklist);
89 }
90
91 completeEphemeralValues(Visited, Worklist, EphValues);
92}
93
94void CodeMetrics::collectEphemeralValues(
95 const Function *F, AssumptionCache *AC,
96 SmallPtrSetImpl<const Value *> &EphValues) {
97 SmallPtrSet<const Value *, 32> Visited;
98 SmallVector<const Value *, 16> Worklist;
99
100 for (auto &AssumeVH : AC->assumptions()) {
101 if (!AssumeVH)
102 continue;
103 Instruction *I = cast<Instruction>(Val&: AssumeVH);
104 assert(I->getParent()->getParent() == F &&
105 "Found assumption for the wrong function!");
106
107 if (EphValues.insert(Ptr: I).second)
108 appendSpeculatableOperands(V: I, Visited, Worklist);
109 }
110
111 completeEphemeralValues(Visited, Worklist, EphValues);
112}
113
114/// Fill in the current structure with information gleaned from the specified
115/// block.
116void CodeMetrics::analyzeBasicBlock(
117 const BasicBlock *BB, const TargetTransformInfo &TTI,
118 const SmallPtrSetImpl<const Value *> &EphValues, bool PrepareForLTO) {
119 ++NumBlocks;
120 InstructionCost NumInstsBeforeThisBB = NumInsts;
121 for (const Instruction &I : *BB) {
122 // Skip ephemeral values.
123 if (EphValues.count(Ptr: &I))
124 continue;
125
126 // Special handling for calls.
127 if (const auto *Call = dyn_cast<CallBase>(Val: &I)) {
128 if (const Function *F = Call->getCalledFunction()) {
129 bool IsLoweredToCall = TTI.isLoweredToCall(F);
130 // If a function is both internal and has a single use, then it is
131 // extremely likely to get inlined in the future (it was probably
132 // exposed by an interleaved devirtualization pass).
133 // When preparing for LTO, liberally consider calls as inline
134 // candidates.
135 if (!Call->isNoInline() && IsLoweredToCall &&
136 ((F->hasInternalLinkage() && F->hasOneLiveUse()) ||
137 PrepareForLTO)) {
138 ++NumInlineCandidates;
139 }
140
141 // If this call is to function itself, then the function is recursive.
142 // Inlining it into other functions is a bad idea, because this is
143 // basically just a form of loop peeling, and our metrics aren't useful
144 // for that case.
145 if (F == BB->getParent())
146 isRecursive = true;
147
148 if (IsLoweredToCall)
149 ++NumCalls;
150 } else {
151 // We don't want inline asm to count as a call - that would prevent loop
152 // unrolling. The argument setup cost is still real, though.
153 if (!Call->isInlineAsm())
154 ++NumCalls;
155 }
156 }
157
158 if (const AllocaInst *AI = dyn_cast<AllocaInst>(Val: &I)) {
159 if (!AI->isStaticAlloca())
160 this->usesDynamicAlloca = true;
161 }
162
163 if (isa<ExtractElementInst>(Val: I) || I.getType()->isVectorTy())
164 ++NumVectorInsts;
165
166 if (I.getType()->isTokenTy() && I.isUsedOutsideOfBlock(BB))
167 notDuplicatable = true;
168
169 if (const CallInst *CI = dyn_cast<CallInst>(Val: &I)) {
170 if (CI->cannotDuplicate())
171 notDuplicatable = true;
172 if (CI->isConvergent())
173 convergent = true;
174 }
175
176 if (const InvokeInst *InvI = dyn_cast<InvokeInst>(Val: &I))
177 if (InvI->cannotDuplicate())
178 notDuplicatable = true;
179
180 NumInsts += TTI.getInstructionCost(U: &I, CostKind: TargetTransformInfo::TCK_CodeSize);
181 }
182
183 if (isa<ReturnInst>(Val: BB->getTerminator()))
184 ++NumRets;
185
186 // We never want to inline functions that contain an indirectbr. This is
187 // incorrect because all the blockaddress's (in static global initializers
188 // for example) would be referring to the original function, and this indirect
189 // jump would jump from the inlined copy of the function into the original
190 // function which is extremely undefined behavior.
191 // FIXME: This logic isn't really right; we can safely inline functions
192 // with indirectbr's as long as no other function or global references the
193 // blockaddress of a block within the current function. And as a QOI issue,
194 // if someone is using a blockaddress without an indirectbr, and that
195 // reference somehow ends up in another function or global, we probably
196 // don't want to inline this function.
197 notDuplicatable |= isa<IndirectBrInst>(Val: BB->getTerminator());
198
199 // Remember NumInsts for this BB.
200 InstructionCost NumInstsThisBB = NumInsts - NumInstsBeforeThisBB;
201 NumBBInsts[BB] = NumInstsThisBB;
202}
203

source code of llvm/lib/Analysis/CodeMetrics.cpp