[PATCH] D16622: Value: Provide a shortcut in stripPointerCastsAndOffsets()

[David Blaikie via llvm-commits]

On Tue, Jan 26, 2016 at 8:15 PM, Matthias Braun via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> MatzeB created this revision.
> MatzeB added reviewers: chandlerc, sunfish, baldrick.
> MatzeB added a subscriber: llvm-commits.
> MatzeB set the repository for this revision to rL LLVM.
> Herald added a subscriber: mcrosier.
>
> The majority of stripPointerCastsAndOffsets() queries can be resolved
> after checking 1 or 2 values. This patch delays the creation and
> insertion into a SmallPtrSet until we have to check more than that. This
> slightly improves compile time in my benchmarks.
>
> Repository:
>   rL LLVM
>
> http://reviews.llvm.org/D16622
>
> Files:
>   lib/IR/Value.cpp
>
> Index: lib/IR/Value.cpp
> ===================================================================
> --- lib/IR/Value.cpp
> +++ lib/IR/Value.cpp
> @@ -421,43 +421,59 @@
>  };
>
>  template <PointerStripKind StripKind>
> +static Value *stripOne(Value *V) {
> +  if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
> +    switch (StripKind) {
> +    case PSK_ZeroIndicesAndAliases:
> +    case PSK_ZeroIndices:
> +      if (!GEP->hasAllZeroIndices())
> +        return nullptr;
> +      break;
> +    case PSK_InBoundsConstantIndices:
> +      if (!GEP->hasAllConstantIndices())
> +        return nullptr;
> +      // fallthrough
> +    case PSK_InBounds:
> +      if (!GEP->isInBounds())
> +        return nullptr;
> +      break;
> +    }
> +    return GEP->getPointerOperand();
> +  } else if (Operator::getOpcode(V) == Instruction::BitCast ||
>

Drop the "else after return"s here.


> +             Operator::getOpcode(V) == Instruction::AddrSpaceCast) {
> +    return cast<Operator>(V)->getOperand(0);
> +  } else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
> +    if (StripKind == PSK_ZeroIndices || GA->mayBeOverridden())
> +      return nullptr;
> +    return GA->getAliasee();
> +  } else {
> +    return nullptr;
> +  }
> +}
> +
> +template <PointerStripKind StripKind>
>  static Value *stripPointerCastsAndOffsets(Value *V) {
>    if (!V->getType()->isPointerTy())
>      return V;
>
> +  // This function is performance sensitive so try the common case first
> +  // before constructing the SmallPtrSet.
> +  Value *Next = stripOne<StripKind>(V);
> +  if (Next == nullptr)
> +    return V;
> +
>    // Even though we don't look through PHI nodes, we could be called on an
>    // instruction in an unreachable block, which may be on a cycle.
>    SmallPtrSet<Value *, 4> Visited;
> -
>    Visited.insert(V);
> +  if (!Visited.insert(Next).second)
> +    return Next;
> +  V = Next;
>    do {
> -    if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
> -      switch (StripKind) {
> -      case PSK_ZeroIndicesAndAliases:
> -      case PSK_ZeroIndices:
> -        if (!GEP->hasAllZeroIndices())
> -          return V;
> -        break;
> -      case PSK_InBoundsConstantIndices:
> -        if (!GEP->hasAllConstantIndices())
> -          return V;
> -        // fallthrough
> -      case PSK_InBounds:
> -        if (!GEP->isInBounds())
> -          return V;
> -        break;
> -      }
> -      V = GEP->getPointerOperand();
> -    } else if (Operator::getOpcode(V) == Instruction::BitCast ||
> -               Operator::getOpcode(V) == Instruction::AddrSpaceCast) {
> -      V = cast<Operator>(V)->getOperand(0);
> -    } else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
> -      if (StripKind == PSK_ZeroIndices || GA->mayBeOverridden())
> -        return V;
> -      V = GA->getAliasee();
> -    } else {
> +    Next = stripOne<StripKind>(V);
> +    if (Next == nullptr)
>        return V;
> -    }
> +    V = Next;
>      assert(V->getType()->isPointerTy() && "Unexpected operand type!");
>    } while (Visited.insert(V).second);
>
>
>
>
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