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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 /// Fill in the current structure with information gleaned from the specified
    104 /// 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 (const Instruction &I : *BB) {
    111     // Skip ephemeral values.
    112     if (EphValues.count(&I))
    113       continue;
    114 
    115     // Special handling for calls.
    116     if (isa<CallInst>(I) || isa<InvokeInst>(I)) {
    117       ImmutableCallSite CS(&I);
    118 
    119       if (const Function *F = CS.getCalledFunction()) {
    120         // If a function is both internal and has a single use, then it is
    121         // extremely likely to get inlined in the future (it was probably
    122         // exposed by an interleaved devirtualization pass).
    123         if (!CS.isNoInline() && F->hasInternalLinkage() && F->hasOneUse())
    124           ++NumInlineCandidates;
    125 
    126         // If this call is to function itself, then the function is recursive.
    127         // Inlining it into other functions is a bad idea, because this is
    128         // basically just a form of loop peeling, and our metrics aren't useful
    129         // for that case.
    130         if (F == BB->getParent())
    131           isRecursive = true;
    132 
    133         if (TTI.isLoweredToCall(F))
    134           ++NumCalls;
    135       } else {
    136         // We don't want inline asm to count as a call - that would prevent loop
    137         // unrolling. The argument setup cost is still real, though.
    138         if (!isa<InlineAsm>(CS.getCalledValue()))
    139           ++NumCalls;
    140       }
    141     }
    142 
    143     if (const AllocaInst *AI = dyn_cast<AllocaInst>(&I)) {
    144       if (!AI->isStaticAlloca())
    145         this->usesDynamicAlloca = true;
    146     }
    147 
    148     if (isa<ExtractElementInst>(I) || I.getType()->isVectorTy())
    149       ++NumVectorInsts;
    150 
    151     if (I.getType()->isTokenTy() && I.isUsedOutsideOfBlock(BB))
    152       notDuplicatable = true;
    153 
    154     if (const CallInst *CI = dyn_cast<CallInst>(&I)) {
    155       if (CI->cannotDuplicate())
    156         notDuplicatable = true;
    157       if (CI->isConvergent())
    158         convergent = true;
    159     }
    160 
    161     if (const InvokeInst *InvI = dyn_cast<InvokeInst>(&I))
    162       if (InvI->cannotDuplicate())
    163         notDuplicatable = true;
    164 
    165     NumInsts += TTI.getUserCost(&I);
    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 }
    187