[PATCH] D63318: [DAGCombine] Teach DAGCombine to fold the aext + select pattern

[Sanjay Patel via Phabricator via llvm-commits]

spatel added inline comments.


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Comment at: llvm/test/CodeGen/X86/cmov-promotion.ll:59
 ; CMOV-NEXT:    movl $255, %eax
-; CMOV-NEXT:    cmovnel %ecx, %eax
+; CMOV-NEXT:    cmovneq %rcx, %rax
 ; CMOV-NEXT:    retq
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steven.zhang wrote:
> craig.topper wrote:
> > The zextisfree check isn't enough to fix this :( It's an i8->i64 zext which isn't free. I guess we'll have to handle this in the x86 backend.
> Yes. The hook only check the type i32->i64. Do we need to pass the value instead of the type for the isZextFree to fix this issue ?
I don't think changing the TLI call will be enough to solve the general problem (the IR is likely already in the form that we're trying to avoid).


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https://reviews.llvm.org/D63318