[llvm] [Support][KnownFPClass] Generalize scaling refinement to an exponent range (PR #215094)

[via llvm-commits]

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@@ -952,3 +952,161 @@ define float @ret_fmul__not_inf__fsub_floor_pat_wrong_floor_val(float nofpclass(
   %mul = fmul float %x, %y.sub.floor.y
   ret float %mul
 }
+
+; The same bound applies when the other operand is a constant.
+define float @ret_fmul__not_inf__fsub_floor_pat_const(float %y) {
+; CHECK-LABEL: define nofpclass(inf) float @ret_fmul__not_inf__fsub_floor_pat_const(
+; CHECK-SAME: float [[Y:%.*]]) #[[ATTR0]] {
+; CHECK-NEXT:    [[FLOOR_Y:%.*]] = call float @llvm.floor.f32(float [[Y]]) #[[ATTR5]]
+; CHECK-NEXT:    [[Y_SUB_FLOOR_Y:%.*]] = fsub float [[Y]], [[FLOOR_Y]]
+; CHECK-NEXT:    [[MUL:%.*]] = fmul float [[Y_SUB_FLOOR_Y]], 3.000000e+00
+; CHECK-NEXT:    ret float [[MUL]]
+;
+  %floor.y = call float @llvm.floor.f32(float %y)
+  %y.sub.floor.y = fsub float %y, %floor.y
+  %mul = fmul float %y.sub.floor.y, 3.0
+  ret float %mul
+}
+
+; Multiplying by a constant of magnitude >= 1 cannot underflow.
+define float @ret_fmul_nozerosub_const_1_5(float nofpclass(zero sub) %x) {
+; CHECK-LABEL: define nofpclass(zero sub) float @ret_fmul_nozerosub_const_1_5(
+; CHECK-SAME: float nofpclass(zero sub) [[X:%.*]]) #[[ATTR0]] {
+; CHECK-NEXT:    [[MUL:%.*]] = fmul float [[X]], 1.500000e+00
+; CHECK-NEXT:    ret float [[MUL]]
+;
+  %mul = fmul float %x, 1.5
+  ret float %mul
+}
+
+; Negative test, 0.75 is less than one.
+define float @ret_fmul_nozerosub_const_0_75(float nofpclass(zero sub) %x) {
+; CHECK-LABEL: define float @ret_fmul_nozerosub_const_0_75(
+; CHECK-SAME: float nofpclass(zero sub) [[X:%.*]]) #[[ATTR0]] {
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ZERICO2005 wrote:

Actually, maybe we can deal with the rounding-mode improvements in a future PR. I haven't seen any correctness issues with regards to the rounding in this PR currently.

https://github.com/llvm/llvm-project/pull/215094