xref: /freebsd/contrib/llvm-project/llvm/lib/Analysis/CodeMetrics.cpp (revision 06e20d1babecec1f45ffda513f55a8db5f1c0f56)
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 
22 #define DEBUG_TYPE "code-metrics"
23 
24 using namespace llvm;
25 
26 static void
27 appendSpeculatableOperands(const Value *V,
28                            SmallPtrSetImpl<const Value *> &Visited,
29                            SmallVectorImpl<const Value *> &Worklist) {
30   const User *U = dyn_cast<User>(V);
31   if (!U)
32     return;
33 
34   for (const Value *Operand : U->operands())
35     if (Visited.insert(Operand).second)
36       if (isSafeToSpeculativelyExecute(Operand))
37         Worklist.push_back(Operand);
38 }
39 
40 static void completeEphemeralValues(SmallPtrSetImpl<const Value *> &Visited,
41                                     SmallVectorImpl<const Value *> &Worklist,
42                                     SmallPtrSetImpl<const Value *> &EphValues) {
43   // Note: We don't speculate PHIs here, so we'll miss instruction chains kept
44   // alive only by ephemeral values.
45 
46   // Walk the worklist using an index but without caching the size so we can
47   // append more entries as we process the worklist. This forms a queue without
48   // quadratic behavior by just leaving processed nodes at the head of the
49   // worklist forever.
50   for (int i = 0; i < (int)Worklist.size(); ++i) {
51     const Value *V = Worklist[i];
52 
53     assert(Visited.count(V) &&
54            "Failed to add a worklist entry to our visited set!");
55 
56     // If all uses of this value are ephemeral, then so is this value.
57     if (!all_of(V->users(), [&](const User *U) { return EphValues.count(U); }))
58       continue;
59 
60     EphValues.insert(V);
61     LLVM_DEBUG(dbgs() << "Ephemeral Value: " << *V << "\n");
62 
63     // Append any more operands to consider.
64     appendSpeculatableOperands(V, Visited, Worklist);
65   }
66 }
67 
68 // Find all ephemeral values.
69 void CodeMetrics::collectEphemeralValues(
70     const Loop *L, AssumptionCache *AC,
71     SmallPtrSetImpl<const Value *> &EphValues) {
72   SmallPtrSet<const Value *, 32> Visited;
73   SmallVector<const Value *, 16> Worklist;
74 
75   for (auto &AssumeVH : AC->assumptions()) {
76     if (!AssumeVH)
77       continue;
78     Instruction *I = cast<Instruction>(AssumeVH);
79 
80     // Filter out call sites outside of the loop so we don't do a function's
81     // worth of work for each of its loops (and, in the common case, ephemeral
82     // values in the loop are likely due to @llvm.assume calls in the loop).
83     if (!L->contains(I->getParent()))
84       continue;
85 
86     if (EphValues.insert(I).second)
87       appendSpeculatableOperands(I, Visited, Worklist);
88   }
89 
90   completeEphemeralValues(Visited, Worklist, EphValues);
91 }
92 
93 void CodeMetrics::collectEphemeralValues(
94     const Function *F, AssumptionCache *AC,
95     SmallPtrSetImpl<const Value *> &EphValues) {
96   SmallPtrSet<const Value *, 32> Visited;
97   SmallVector<const Value *, 16> Worklist;
98 
99   for (auto &AssumeVH : AC->assumptions()) {
100     if (!AssumeVH)
101       continue;
102     Instruction *I = cast<Instruction>(AssumeVH);
103     assert(I->getParent()->getParent() == F &&
104            "Found assumption for the wrong function!");
105 
106     if (EphValues.insert(I).second)
107       appendSpeculatableOperands(I, Visited, Worklist);
108   }
109 
110   completeEphemeralValues(Visited, Worklist, EphValues);
111 }
112 
113 /// Fill in the current structure with information gleaned from the specified
114 /// block.
115 void CodeMetrics::analyzeBasicBlock(const BasicBlock *BB,
116                                     const TargetTransformInfo &TTI,
117                                     const SmallPtrSetImpl<const Value*> &EphValues) {
118   ++NumBlocks;
119   unsigned NumInstsBeforeThisBB = NumInsts;
120   for (const Instruction &I : *BB) {
121     // Skip ephemeral values.
122     if (EphValues.count(&I))
123       continue;
124 
125     // Special handling for calls.
126     if (const auto *Call = dyn_cast<CallBase>(&I)) {
127       if (const Function *F = Call->getCalledFunction()) {
128         // If a function is both internal and has a single use, then it is
129         // extremely likely to get inlined in the future (it was probably
130         // exposed by an interleaved devirtualization pass).
131         if (!Call->isNoInline() && F->hasInternalLinkage() && F->hasOneUse())
132           ++NumInlineCandidates;
133 
134         // If this call is to function itself, then the function is recursive.
135         // Inlining it into other functions is a bad idea, because this is
136         // basically just a form of loop peeling, and our metrics aren't useful
137         // for that case.
138         if (F == BB->getParent())
139           isRecursive = true;
140 
141         if (TTI.isLoweredToCall(F))
142           ++NumCalls;
143       } else {
144         // We don't want inline asm to count as a call - that would prevent loop
145         // unrolling. The argument setup cost is still real, though.
146         if (!Call->isInlineAsm())
147           ++NumCalls;
148       }
149     }
150 
151     if (const AllocaInst *AI = dyn_cast<AllocaInst>(&I)) {
152       if (!AI->isStaticAlloca())
153         this->usesDynamicAlloca = true;
154     }
155 
156     if (isa<ExtractElementInst>(I) || I.getType()->isVectorTy())
157       ++NumVectorInsts;
158 
159     if (I.getType()->isTokenTy() && I.isUsedOutsideOfBlock(BB))
160       notDuplicatable = true;
161 
162     if (const CallInst *CI = dyn_cast<CallInst>(&I)) {
163       if (CI->cannotDuplicate())
164         notDuplicatable = true;
165       if (CI->isConvergent())
166         convergent = true;
167     }
168 
169     if (const InvokeInst *InvI = dyn_cast<InvokeInst>(&I))
170       if (InvI->cannotDuplicate())
171         notDuplicatable = true;
172 
173     NumInsts += TTI.getUserCost(&I, TargetTransformInfo::TCK_CodeSize);
174   }
175 
176   if (isa<ReturnInst>(BB->getTerminator()))
177     ++NumRets;
178 
179   // We never want to inline functions that contain an indirectbr.  This is
180   // incorrect because all the blockaddress's (in static global initializers
181   // for example) would be referring to the original function, and this indirect
182   // jump would jump from the inlined copy of the function into the original
183   // function which is extremely undefined behavior.
184   // FIXME: This logic isn't really right; we can safely inline functions
185   // with indirectbr's as long as no other function or global references the
186   // blockaddress of a block within the current function.  And as a QOI issue,
187   // if someone is using a blockaddress without an indirectbr, and that
188   // reference somehow ends up in another function or global, we probably
189   // don't want to inline this function.
190   notDuplicatable |= isa<IndirectBrInst>(BB->getTerminator());
191 
192   // Remember NumInsts for this BB.
193   NumBBInsts[BB] = NumInsts - NumInstsBeforeThisBB;
194 }
195