[llvm] r215966 - IR: Reduce RAUW traffic in ConstantVector

[Aaron Ballman]

I have reverted from this revision to r215957 (skipping only 215961 &
215962 as they were unrelated) due to breaking MSVC with asserts. The
assert is one in std::equal because it cannot be passed a nullptr,
which your commits seemed to be doing. Since the patches all built on
top of one another, I had to revert them in a block, sorry if this
causes problems for you!

~Aaron

On Mon, Aug 18, 2014 at 10:24 PM, Duncan P. N. Exon Smith
<dexonsmith at apple.com> wrote:
> Author: dexonsmith
> Date: Mon Aug 18 21:24:46 2014
> New Revision: 215966
>
> URL: http://llvm.org/viewvc/llvm-project?rev=215966&view=rev
> Log:
> IR: Reduce RAUW traffic in ConstantVector
>
> Avoid creating a new `ConstantVector` on an RAUW of one of its members.
> This reduces RAUW traffic on any containing constant.
>
> This is part of PR20515.
>
> Modified:
>     llvm/trunk/lib/IR/Constants.cpp
>
> Modified: llvm/trunk/lib/IR/Constants.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/Constants.cpp?rev=215966&r1=215965&r2=215966&view=diff
> ==============================================================================
> --- llvm/trunk/lib/IR/Constants.cpp (original)
> +++ llvm/trunk/lib/IR/Constants.cpp Mon Aug 18 21:24:46 2014
> @@ -2810,17 +2810,41 @@ void ConstantStruct::replaceUsesOfWithOn
>  void ConstantVector::replaceUsesOfWithOnConstant(Value *From, Value *To,
>                                                   Use *U) {
>    assert(isa<Constant>(To) && "Cannot make Constant refer to non-constant!");
> +  Constant *ToC = cast<Constant>(To);
>
>    SmallVector<Constant*, 8> Values;
>    Values.reserve(getNumOperands());  // Build replacement array...
> +  unsigned NumUpdated = 0;
>    for (unsigned i = 0, e = getNumOperands(); i != e; ++i) {
>      Constant *Val = getOperand(i);
> -    if (Val == From) Val = cast<Constant>(To);
> +    if (Val == From) {
> +      ++NumUpdated;
> +      Val = ToC;
> +    }
>      Values.push_back(Val);
>    }
>
> -  Constant *Replacement = get(Values);
> -  replaceUsesOfWithOnConstantImpl(Replacement);
> +  if (Constant *C = getImpl(Values)) {
> +    replaceUsesOfWithOnConstantImpl(C);
> +    return;
> +  }
> +
> +  // Update to the new value.  Optimize for the case when we have a single
> +  // operand that we're changing, but handle bulk updates efficiently.
> +  auto &pImpl = getType()->getContext().pImpl;
> +  pImpl->VectorConstants.remove(this);
> +
> +  if (NumUpdated == 1) {
> +    unsigned OperandToUpdate = U - OperandList;
> +    assert(getOperand(OperandToUpdate) == From && "ReplaceAllUsesWith broken!");
> +    setOperand(OperandToUpdate, ToC);
> +  } else {
> +    for (unsigned I = 0, E = getNumOperands(); I != E; ++I)
> +      if (getOperand(I) == From)
> +        setOperand(I, ToC);
> +  }
> +
> +  pImpl->VectorConstants.insert(this);
>  }
>
>  void ConstantExpr::replaceUsesOfWithOnConstant(Value *From, Value *ToV,
>
>
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