[InstCombine] Adding testcase for Z / (1.0 / Y) => (Y * Z)

[raghesh]

Summary

The added testcase shows the current transformation for the operation
Z / (1.0 / Y), which remains unchanged. This will be updated to align
with the transformed code (Y * Z) in a later patch.

The existing transformation Z / (X / Y) => (Y * Z) / X is not handling
this case as there are multiple uses for (1.0 / Y) in this testcase.

[spatel]

LGTM - I'll try to push this on behalf of the author shortly.

[spatel]

llvm/test/Transforms/InstCombine/fdiv.ll

200

I overlooked this earlier, but you probably want to change this from 'fast' to whatever the minimal flags are. It's fine to do that in the other patch/review if you want.

'arcp reassoc'?

[raghesh]

llvm/test/Transforms/InstCombine/fdiv.ll

200

Changed 'fast' to 'arc reassoc' by creating a new revision https://reviews.llvm.org/D72431

llvm/test/Transforms/InstCombine/fdiv.ll

 ; CHECK-NEXT:    ret float [[DIV2]]
 ;
   %div1 = fdiv float %x, %y
   %div2 = fdiv fast float %z, %div1
   call void @use_f32(float %div1)
   ret float %div2
 }
 
+; Z / (1.0 / Y)
+
+define float @div_with_div_denominator_with_one_as_numerator_extra_use(float %x, float %y, float %z) {
+; CHECK-LABEL: @div_with_div_denominator_with_one_as_numerator_extra_use(
+; CHECK-NEXT:    [[DIV1:%.*]] = fdiv float 1.000000e+00, [[Y:%.*]]
+; CHECK-NEXT:    [[DIV2:%.*]] = fdiv fast float [[Z:%.*]], [[DIV1]]
+; CHECK-NEXT:    call void @use_f32(float [[DIV1]])
+; CHECK-NEXT:    ret float [[DIV2]]
+;
+  %div1 = fdiv float 1.0, %y
+  %div2 = fdiv fast float %z, %div1
+  call void @use_f32(float %div1)
+  ret float %div2
+}
+
 define float @fneg_fneg(float %x, float %y) {
 ; CHECK-LABEL: @fneg_fneg(
 ; CHECK-NEXT:    [[DIV:%.*]] = fdiv float [[X:%.*]], [[Y:%.*]]
 ; CHECK-NEXT:    ret float [[DIV]]
 ;
   %x.fneg = fsub float -0.0, %x
   %y.fneg = fsub float -0.0, %y
   %div = fdiv float %x.fneg, %y.fneg