[PATCH] D45585: [DAGCombiner][X86] When promoting loads don't use ZEXTLOAD even its legal

[Craig Topper via Phabricator via llvm-commits]

craig.topper added inline comments.


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Comment at: test/CodeGen/X86/mul-constant-i16.ll:75
 ; X86:       # %bb.0:
-; X86-NEXT:    movzwl {{[0-9]+}}(%esp), %eax
-; X86-NEXT:    leal (%eax,%eax,4), %eax
+; X86-NEXT:    imull $5, {{[0-9]+}}(%esp), %eax
 ; X86-NEXT:    # kill: def $ax killed $ax killed $eax
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RKSimon wrote:
> These are likely to be performance regressions on most targets - the special case x86 'MulConstantOptimization' patterns in combineMul should still be used where possible.
Agreed. But that issue wasn't caused by this patch. It's pretty easy to hit with 32-bit instructions too.

https://godbolt.org/g/9Pa83o


https://reviews.llvm.org/D45585