[PATCH] D118037: [DAGCombine] Consider SETULT as carry flag

Wed Feb 23 14:03:05 PST 2022

chfast added inline comments.

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Comment at: llvm/test/CodeGen/X86/addcarry.ll:1029
 ; CHECK-NEXT:    cmpl %ecx, %edx
-; CHECK-NEXT:    adcl $0, %eax
+; CHECK-NEXT:    adcl %esi, %eax
 ; CHECK-NEXT:    retq
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RKSimon wrote:
> craig.topper wrote:
> > This case looks like an easy X86 backend peephole.
> > 
> > X86ISD::ADC with an unused flag result, 0 for RHS, LHS is a single use ADD. If so fold the ADD operands into a new X86ISD::ADC.
> > 
> > I'm not sure about the @add_U320_without_i128_add case without staring at it for a lot longer.
> combineSBB already does something similar, we're just missing this from combineADC
See https://reviews.llvm.org/D120435.

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D118037/new/

https://reviews.llvm.org/D118037