[PATCH] D110588: [X86] decomposeMulByConstant - decompose legal vXi32 mutliplies on SlowPMULLD targets

[Craig Topper via Phabricator via llvm-commits]

craig.topper added a comment.

In D110588#3036506 <https://reviews.llvm.org/D110588#3036506>, @RKSimon wrote:

> ping - any thoughts? should we do not do this at all? limit this to SlowPMULLD or always do it for vXi32 and vXi64?

I think it makes sense for SlowPMULLD. I think this makes sense for vXi32 on Haswell and later Intel Core CPUs. That's where it went from one uop to two serialize 5 cycle uops.  I think it makes sense for vXi64 on all Intel CPUs with PMULLQ since that instruction is 3 serialized uops.


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https://reviews.llvm.org/D110588