[PATCH] D33342: [InstCombine] try to canonicalize xor-of-icmps to and-of-icmps

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a comment.

In https://reviews.llvm.org/D33342#768301, @efriedma wrote:

> This approach seems relatively expensive and not very flexible... e.g. we can't even transform "(x < 5) ^ (x == 4)".  Is there really no better way to catch simple cases?


Can you provide an IR example of the case you're thinking of? Did I mistranslate the comment above?

  $ cat xoricmps.ll 
  define i1 @xor_icmps_signed(i8 %x) {
    %cmp1 = icmp slt i8 %x, 5
    %cmp2 = icmp eq i8 %x, 4
    %r = xor i1 %cmp1, %cmp2
    ret i1 %r
  }
  
  define i1 @xor_icmps_unsigned(i8 %x) {
    %cmp1 = icmp ult i8 %x, 5
    %cmp2 = icmp eq i8 %x, 4
    %r = xor i1 %cmp1, %cmp2
    ret i1 %r
  }
  
  $ ./opt -instcombine xoricmps.ll -S
  
  define i1 @xor_icmps_signed(i8 %x) {
    %1 = icmp slt i8 %x, 4
    ret i1 %1
  }
  
  define i1 @xor_icmps_unsigned(i8 %x) {
    %1 = icmp ult i8 %x, 4
    ret i1 %1
  }


https://reviews.llvm.org/D33342