[PATCH] D100091: [X86] Fix wrong handle with "-mno-x87"

[Craig Topper via Phabricator via llvm-commits]

craig.topper added a comment.

In D100091#2707381 <https://reviews.llvm.org/D100091#2707381>, @LiuChen3 wrote:

> In D100091#2677235 <https://reviews.llvm.org/D100091#2677235>, @craig.topper wrote:
>
>> In D100091#2675996 <https://reviews.llvm.org/D100091#2675996>, @LiuChen3 wrote:
>>
>>> In D100091#2675968 <https://reviews.llvm.org/D100091#2675968>, @craig.topper wrote:
>>>
>>>> What about cases that use x87 to do float/double conversions? I think it’s i64 conversions in 32-bit mode. But maybe other cases. Does gcc disable those with -mno-80387?
>>>
>>> You are right! GCC can do the conversions: https://godbolt.org/z/87ez838oc . 
>>> With this patch, llvm will fail in ISEL. I want to make another patch to do this.
>>
>> I'm more concerned about these cases that don't use long double and aren't missed constant folding. https://godbolt.org/z/qGv54ef34
>
> It seems not easy to handle this. I want fix a bug in this patch. For this part, It looks more like a feature. We want to do that in another patch. What's your opinion here?

What is the usage model you’re trying to enable? This has been broken for a long time. Why is it important now?


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https://reviews.llvm.org/D100091