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/Analysis/AssumptionCache.h"
15#include "llvm/Analysis/LoopInfo.h"
16#include "llvm/Analysis/TargetTransformInfo.h"
17#include "llvm/Analysis/ValueTracking.h"
18#include "llvm/IR/DataLayout.h"
19#include "llvm/IR/Function.h"
20#include "llvm/Support/Debug.h"
21#include "llvm/Support/raw_ostream.h"
22
23#define DEBUG_TYPE "code-metrics"
24
25using namespace llvm;
26
27static void
28appendSpeculatableOperands(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 (isSafeToSpeculativelyExecute(Operand))
38        Worklist.push_back(Operand);
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(V->users(), [&](const User *U) { return EphValues.count(U); }))
59      continue;
60
61    EphValues.insert(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>(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(I->getParent()))
85      continue;
86
87    if (EphValues.insert(I).second)
88      appendSpeculatableOperands(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>(AssumeVH);
104    assert(I->getParent()->getParent() == F &&
105           "Found assumption for the wrong function!");
106
107    if (EphValues.insert(I).second)
108      appendSpeculatableOperands(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(const BasicBlock *BB,
117                                    const TargetTransformInfo &TTI,
118                                    const SmallPtrSetImpl<const Value*> &EphValues) {
119  ++NumBlocks;
120  unsigned NumInstsBeforeThisBB = NumInsts;
121  for (const Instruction &I : *BB) {
122    // Skip ephemeral values.
123    if (EphValues.count(&I))
124      continue;
125
126    // Special handling for calls.
127    if (const auto *Call = dyn_cast<CallBase>(&I)) {
128      if (const Function *F = Call->getCalledFunction()) {
129        // If a function is both internal and has a single use, then it is
130        // extremely likely to get inlined in the future (it was probably
131        // exposed by an interleaved devirtualization pass).
132        if (!Call->isNoInline() && F->hasInternalLinkage() && F->hasOneUse())
133          ++NumInlineCandidates;
134
135        // If this call is to function itself, then the function is recursive.
136        // Inlining it into other functions is a bad idea, because this is
137        // basically just a form of loop peeling, and our metrics aren't useful
138        // for that case.
139        if (F == BB->getParent())
140          isRecursive = true;
141
142        if (TTI.isLoweredToCall(F))
143          ++NumCalls;
144      } else {
145        // We don't want inline asm to count as a call - that would prevent loop
146        // unrolling. The argument setup cost is still real, though.
147        if (!Call->isInlineAsm())
148          ++NumCalls;
149      }
150    }
151
152    if (const AllocaInst *AI = dyn_cast<AllocaInst>(&I)) {
153      if (!AI->isStaticAlloca())
154        this->usesDynamicAlloca = true;
155    }
156
157    if (isa<ExtractElementInst>(I) || I.getType()->isVectorTy())
158      ++NumVectorInsts;
159
160    if (I.getType()->isTokenTy() && I.isUsedOutsideOfBlock(BB))
161      notDuplicatable = true;
162
163    if (const CallInst *CI = dyn_cast<CallInst>(&I)) {
164      if (CI->cannotDuplicate())
165        notDuplicatable = true;
166      if (CI->isConvergent())
167        convergent = true;
168    }
169
170    if (const InvokeInst *InvI = dyn_cast<InvokeInst>(&I))
171      if (InvI->cannotDuplicate())
172        notDuplicatable = true;
173
174    NumInsts += TTI.getUserCost(&I);
175  }
176
177  if (isa<ReturnInst>(BB->getTerminator()))
178    ++NumRets;
179
180  // We never want to inline functions that contain an indirectbr.  This is
181  // incorrect because all the blockaddress's (in static global initializers
182  // for example) would be referring to the original function, and this indirect
183  // jump would jump from the inlined copy of the function into the original
184  // function which is extremely undefined behavior.
185  // FIXME: This logic isn't really right; we can safely inline functions
186  // with indirectbr's as long as no other function or global references the
187  // blockaddress of a block within the current function.  And as a QOI issue,
188  // if someone is using a blockaddress without an indirectbr, and that
189  // reference somehow ends up in another function or global, we probably
190  // don't want to inline this function.
191  notDuplicatable |= isa<IndirectBrInst>(BB->getTerminator());
192
193  // Remember NumInsts for this BB.
194  NumBBInsts[BB] = NumInsts - NumInstsBeforeThisBB;
195}
196