[llvm] [InstCombine] Optimise x / sqrt(y / z) with fast-math pattern. (PR #76737)

[Matt Arsenault via llvm-commits]

================
@@ -0,0 +1,85 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -passes=instcombine < %s | FileCheck %s
+
+declare double @llvm.sqrt.f64(double)
+
+define double @sqrt_div_fast(double %x, double %y, double %z) {
+; CHECK-LABEL: @sqrt_div_fast(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = fdiv fast double [[Z:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call fast double @llvm.sqrt.f64(double [[TMP0]])
+; CHECK-NEXT:    [[DIV1:%.*]] = fmul fast double [[TMP1]], [[X:%.*]]
+; CHECK-NEXT:    ret double [[DIV1]]
+;
+entry:
+  %div = fdiv fast double %y, %z
+  %sqrt = call fast double @llvm.sqrt.f64(double %div)
+  %div1 = fdiv fast double %x, %sqrt
+  ret double %div1
+}
+
+define double @sqrt_div(double %x, double %y, double %z) {
+; CHECK-LABEL: @sqrt_div(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[DIV:%.*]] = fdiv double [[Y:%.*]], [[Z:%.*]]
+; CHECK-NEXT:    [[SQRT:%.*]] = call double @llvm.sqrt.f64(double [[DIV]])
+; CHECK-NEXT:    [[DIV1:%.*]] = fdiv double [[X:%.*]], [[SQRT]]
+; CHECK-NEXT:    ret double [[DIV1]]
+;
+entry:
+  %div = fdiv double %y, %z
+  %sqrt = call double @llvm.sqrt.f64(double %div)
+  %div1 = fdiv double %x, %sqrt
+  ret double %div1
+}
+
+define double @sqrt_div_reassoc_arcp(double %x, double %y, double %z) {
+; CHECK-LABEL: @sqrt_div_reassoc_arcp(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = fdiv reassoc arcp double [[Z:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call reassoc arcp double @llvm.sqrt.f64(double [[TMP0]])
+; CHECK-NEXT:    [[DIV1:%.*]] = fmul reassoc arcp double [[TMP1]], [[X:%.*]]
+; CHECK-NEXT:    ret double [[DIV1]]
+;
+entry:
+  %div = fdiv reassoc arcp double %y, %z
+  %sqrt = call reassoc arcp double @llvm.sqrt.f64(double %div)
+  %div1 = fdiv reassoc arcp double %x, %sqrt
+  ret double %div1
+}
+
+declare void @use(double)
+define double @sqrt_div_fast_multiple_uses_1(double %x, double %y, double %z) {
+; CHECK-LABEL: @sqrt_div_fast_multiple_uses_1(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[DIV:%.*]] = fdiv fast double [[Y:%.*]], [[Z:%.*]]
+; CHECK-NEXT:    call void @use(double [[DIV]])
+; CHECK-NEXT:    [[SQRT:%.*]] = call fast double @llvm.sqrt.f64(double [[DIV]])
+; CHECK-NEXT:    [[DIV1:%.*]] = fdiv fast double [[X:%.*]], [[SQRT]]
+; CHECK-NEXT:    ret double [[DIV1]]
+;
+entry:
+  %div = fdiv fast double %y, %z
+  call void @use(double %div)
+  %sqrt = call fast double @llvm.sqrt.f64(double %div)
+  %div1 = fdiv fast double %x, %sqrt
----------------
arsenm wrote:

Yes, I think so 

https://github.com/llvm/llvm-project/pull/76737