xref: /freebsd/contrib/llvm-project/llvm/lib/Analysis/CodeMetrics.cpp (revision c7a063741720ef81d4caa4613242579d12f1d605)
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/Analysis/ValueTracking.h"
19 #include "llvm/IR/Function.h"
20 #include "llvm/Support/Debug.h"
21 #include "llvm/Support/InstructionCost.h"
22 
23 #define DEBUG_TYPE "code-metrics"
24 
25 using namespace llvm;
26 
27 static void
28 appendSpeculatableOperands(const Value *V,
29                            SmallPtrSetImpl<const Value *> &Visited,
30                            SmallVectorImpl<const Value *> &Worklist) {
31   const User *U = dyn_cast<User>(V);
32   if (!U)
33     return;
34 
35   for (const Value *Operand : U->operands())
36     if (Visited.insert(Operand).second)
37       if (const auto *I = dyn_cast<Instruction>(Operand))
38         if (!I->mayHaveSideEffects() && !I->isTerminator())
39           Worklist.push_back(I);
40 }
41 
42 static void completeEphemeralValues(SmallPtrSetImpl<const Value *> &Visited,
43                                     SmallVectorImpl<const Value *> &Worklist,
44                                     SmallPtrSetImpl<const Value *> &EphValues) {
45   // Note: We don't speculate PHIs here, so we'll miss instruction chains kept
46   // alive only by ephemeral values.
47 
48   // Walk the worklist using an index but without caching the size so we can
49   // append more entries as we process the worklist. This forms a queue without
50   // quadratic behavior by just leaving processed nodes at the head of the
51   // worklist forever.
52   for (int i = 0; i < (int)Worklist.size(); ++i) {
53     const Value *V = Worklist[i];
54 
55     assert(Visited.count(V) &&
56            "Failed to add a worklist entry to our visited set!");
57 
58     // If all uses of this value are ephemeral, then so is this value.
59     if (!all_of(V->users(), [&](const User *U) { return EphValues.count(U); }))
60       continue;
61 
62     EphValues.insert(V);
63     LLVM_DEBUG(dbgs() << "Ephemeral Value: " << *V << "\n");
64 
65     // Append any more operands to consider.
66     appendSpeculatableOperands(V, Visited, Worklist);
67   }
68 }
69 
70 // Find all ephemeral values.
71 void CodeMetrics::collectEphemeralValues(
72     const Loop *L, AssumptionCache *AC,
73     SmallPtrSetImpl<const Value *> &EphValues) {
74   SmallPtrSet<const Value *, 32> Visited;
75   SmallVector<const Value *, 16> Worklist;
76 
77   for (auto &AssumeVH : AC->assumptions()) {
78     if (!AssumeVH)
79       continue;
80     Instruction *I = cast<Instruction>(AssumeVH);
81 
82     // Filter out call sites outside of the loop so we don't do a function's
83     // worth of work for each of its loops (and, in the common case, ephemeral
84     // values in the loop are likely due to @llvm.assume calls in the loop).
85     if (!L->contains(I->getParent()))
86       continue;
87 
88     if (EphValues.insert(I).second)
89       appendSpeculatableOperands(I, Visited, Worklist);
90   }
91 
92   completeEphemeralValues(Visited, Worklist, EphValues);
93 }
94 
95 void CodeMetrics::collectEphemeralValues(
96     const Function *F, AssumptionCache *AC,
97     SmallPtrSetImpl<const Value *> &EphValues) {
98   SmallPtrSet<const Value *, 32> Visited;
99   SmallVector<const Value *, 16> Worklist;
100 
101   for (auto &AssumeVH : AC->assumptions()) {
102     if (!AssumeVH)
103       continue;
104     Instruction *I = cast<Instruction>(AssumeVH);
105     assert(I->getParent()->getParent() == F &&
106            "Found assumption for the wrong function!");
107 
108     if (EphValues.insert(I).second)
109       appendSpeculatableOperands(I, Visited, Worklist);
110   }
111 
112   completeEphemeralValues(Visited, Worklist, EphValues);
113 }
114 
115 /// Fill in the current structure with information gleaned from the specified
116 /// block.
117 void CodeMetrics::analyzeBasicBlock(
118     const BasicBlock *BB, const TargetTransformInfo &TTI,
119     const SmallPtrSetImpl<const Value *> &EphValues, bool PrepareForLTO) {
120   ++NumBlocks;
121   // Use a proxy variable for NumInsts of type InstructionCost, so that it can
122   // use InstructionCost's arithmetic properties such as saturation when this
123   // feature is added to InstructionCost.
124   // When storing the value back to NumInsts, we can assume all costs are Valid
125   // because the IR should not contain any nodes that cannot be costed. If that
126   // happens the cost-model is broken.
127   InstructionCost NumInstsProxy = NumInsts;
128   InstructionCost NumInstsBeforeThisBB = NumInsts;
129   for (const Instruction &I : *BB) {
130     // Skip ephemeral values.
131     if (EphValues.count(&I))
132       continue;
133 
134     // Special handling for calls.
135     if (const auto *Call = dyn_cast<CallBase>(&I)) {
136       if (const Function *F = Call->getCalledFunction()) {
137         bool IsLoweredToCall = TTI.isLoweredToCall(F);
138         // If a function is both internal and has a single use, then it is
139         // extremely likely to get inlined in the future (it was probably
140         // exposed by an interleaved devirtualization pass).
141         // When preparing for LTO, liberally consider calls as inline
142         // candidates.
143         if (!Call->isNoInline() && IsLoweredToCall &&
144             ((F->hasInternalLinkage() && F->hasOneUse()) || PrepareForLTO)) {
145           ++NumInlineCandidates;
146         }
147 
148         // If this call is to function itself, then the function is recursive.
149         // Inlining it into other functions is a bad idea, because this is
150         // basically just a form of loop peeling, and our metrics aren't useful
151         // for that case.
152         if (F == BB->getParent())
153           isRecursive = true;
154 
155         if (IsLoweredToCall)
156           ++NumCalls;
157       } else {
158         // We don't want inline asm to count as a call - that would prevent loop
159         // unrolling. The argument setup cost is still real, though.
160         if (!Call->isInlineAsm())
161           ++NumCalls;
162       }
163     }
164 
165     if (const AllocaInst *AI = dyn_cast<AllocaInst>(&I)) {
166       if (!AI->isStaticAlloca())
167         this->usesDynamicAlloca = true;
168     }
169 
170     if (isa<ExtractElementInst>(I) || I.getType()->isVectorTy())
171       ++NumVectorInsts;
172 
173     if (I.getType()->isTokenTy() && I.isUsedOutsideOfBlock(BB))
174       notDuplicatable = true;
175 
176     if (const CallInst *CI = dyn_cast<CallInst>(&I)) {
177       if (CI->cannotDuplicate())
178         notDuplicatable = true;
179       if (CI->isConvergent())
180         convergent = true;
181     }
182 
183     if (const InvokeInst *InvI = dyn_cast<InvokeInst>(&I))
184       if (InvI->cannotDuplicate())
185         notDuplicatable = true;
186 
187     NumInstsProxy += TTI.getUserCost(&I, TargetTransformInfo::TCK_CodeSize);
188     NumInsts = *NumInstsProxy.getValue();
189   }
190 
191   if (isa<ReturnInst>(BB->getTerminator()))
192     ++NumRets;
193 
194   // We never want to inline functions that contain an indirectbr.  This is
195   // incorrect because all the blockaddress's (in static global initializers
196   // for example) would be referring to the original function, and this indirect
197   // jump would jump from the inlined copy of the function into the original
198   // function which is extremely undefined behavior.
199   // FIXME: This logic isn't really right; we can safely inline functions
200   // with indirectbr's as long as no other function or global references the
201   // blockaddress of a block within the current function.  And as a QOI issue,
202   // if someone is using a blockaddress without an indirectbr, and that
203   // reference somehow ends up in another function or global, we probably
204   // don't want to inline this function.
205   notDuplicatable |= isa<IndirectBrInst>(BB->getTerminator());
206 
207   // Remember NumInsts for this BB.
208   InstructionCost NumInstsThisBB = NumInstsProxy - NumInstsBeforeThisBB;
209   NumBBInsts[BB] = *NumInstsThisBB.getValue();
210 }
211