[PATCH] D81827: [CGP] Convert phi types

Wed Jun 17 07:31:35 PDT 2020

dmgreen added a comment.

In D81827#2096973 <https://reviews.llvm.org/D81827#2096973>, @efriedma wrote:

> The "used by stores" part is potentially a little problematic, until we settle https://bugs.llvm.org/show_bug.cgi?id=45152 .

Fascinating. Am I right in saying that this would not be a problem under ARM? And only actually be a problem for X86-32 in llvm? I has heavily tempted to put this behind a TLI hook before, and this might be an extra reason. Something like shouldConvertPhiType(Src, Dst).

> The algorithm seems reasonable.
> 
> This needs to happen in CodeGenPrepare due to the interaction with other CGP optimizations?

Yeah. It's related to converting splats to integer. Ideally the whole thing would be done during global-isel style lowering. (I think, although don't know the details, that it might forget and re-learn type information, so I guess it might get something like this for free). For ISel it's done in CGP though.

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https://reviews.llvm.org/D81827