src/llvm/lib/Analysis/CodeMetrics.cpp

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