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
28using namespace llvm;
29
30static 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.
64void 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
86void 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.
105void 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