[PATCH] D67363: [BreakFalseDeps] ignore function with minsize attribute

[Craig Topper via Phabricator via llvm-commits]

craig.topper added a comment.

In D67363#1664746 <https://reviews.llvm.org/D67363#1664746>, @spatel wrote:

> In D67363#1664689 <https://reviews.llvm.org/D67363#1664689>, @craig.topper wrote:
>
> > For VEX instructions don’t we just use the other input register to break the dependency without adding an instruction?
>
>
> That sounds right, but it's not controlled by this pass. That's part of memory op folding?
>  If I'm seeing it correctly, that's already more aggressively optimizing for size than what we're doing here:
>
>   // Avoid partial and undef register update stalls unless optimizing for size.
>   if (!MF.getFunction().hasOptSize() &&
>       (hasPartialRegUpdate(MI.getOpcode(), Subtarget, /*ForLoadFold*/true) ||
>        shouldPreventUndefRegUpdateMemFold(MF, MI)))
>     return nullptr;


We disable folding if it takes away our opportunity to use the other input register. But something still needs to pick a register for the implicit_def operand. I though that was this pass? I think in absense of this pass it may just be set to the xmm0 by the register allocator. Do we have tests where xmm0 isn't the right choice?


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