Missed optimization: fold x*a == b -> x == b/a

[zxt5]

define i1 @src(float %v1) {
 %v2 = fmul float %v1, 5.000000e-01
  %v3 = fcmp olt float %v2, 8.000000e+00
  ret i1 %v3
}

define i1 @tgt(float %v1) {
  %v2 = fcmp olt float %v1, 1.600000e+01
  ret i1 %v2
}

Alive2: https://alive2.llvm.org/ce/z/b6iVdH
Godbolt: https://godbolt.org/z/WPMbTh7GP

Pattern found in https://github.com/dtcxzyw/llvm-opt-benchmark/blob/main/bench/ffmpeg/optimized/af_arnndn.ll

[Seraphimt]

Hi! I am interesting in similar kind issue and I ready do some research, but I have few experience in LLVM yet. If it is ok for you, than assignee me, please!

[dtcxzyw]

@Seraphimt Please read https://llvm.org/docs/InstCombineContributorGuide.html before submitting a patch. Have fun :)

[dtcxzyw]

FYI, the comments in #85267 may help.