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