[PATCH] D31398: [X86][X86 intrinsics]Folding cmp(sub(a, b), 0) into cmp(a, b) optimization

[michael zuckerman via Phabricator via llvm-commits]

m_zuckerman added a comment.

In https://reviews.llvm.org/D31398#716031, @spatel wrote:

> In https://reviews.llvm.org/D31398#716002, @m_zuckerman wrote:
>
> > You are absolutely right, your transform is valid and we will do it after this patch.
> >  Since the intrinsics are lowered with generic IR, mine patch is still valid and we will need them both for a complete solution.
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> 1. We need to be conservative for the general case...speaking from experience :). As @scanon mentioned, we need some way to tell whether denorms are flushed to zero or not. I think this patch is safe currently because we assume the default FP ENV, and on x86 that would not have DAZ/FTZ.
> 2. We don't need nsz or nnan for this fold (see @scanon comment).
> 3. I'd prefer to put all of the tests in one file since they are just variants of the same fold.


1.I agree with you, in the general case we need to be caution, but this transformation is feasible.
Regard the X86 this transformation is safe (As you wrote) from all perspectives. We know that status of the flags and we know the target.

3.I am with you on that.


https://reviews.llvm.org/D31398