[PATCH] D50804: DAG: Fix isKnownNeverNaN for basic non-sNaN cases

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a comment.

The change should be visible in tests because there's a DAGCombine that uses isKnownNeverNaN()?

Try the following with:
$ llc -o - fmaxnm.ll -mtriple=aarch64 -enable-no-signed-zeros-fp-math

  ; This should codegen to fmaxnm with no-signed-zeros.
  
  define float @fmaxnm(i32 %i1, i32 %i2) {
    %f1 = uitofp i32 %i1 to float
    %fadd1 = fadd float %f1, 11.0
    %f2 = uitofp i32 %i2 to float
    %fadd2 = fadd float %f2, 17.0
    %cmp = fcmp uge float %fadd1, %fadd2
    %val = select i1 %cmp, float %fadd1, float %fadd2
    ret float %val
  }
  
  ; If i1 is 0, fmul is NaN because 0.0 * -INF = NaN
  ; Therefore, this is not fmaxnm.
  
  define float @not_fmaxnm(i32 %i1, i32 %i2) {
    %f1 = uitofp i32 %i1 to float
    %fmul = fmul float %f1, 0xfff0000000000000 ; -INFINITY as 64-bit hex
    %f2 = uitofp i32 %i2 to float
    %fadd2 = fadd float %f2, 17.0
    %cmp = fcmp uge float %fmul, %fadd2
    %val = select i1 %cmp, float %fmul, float %fadd2
    ret float %val
  }


https://reviews.llvm.org/D50804