[clang] clang: Add pragma clang fp reciprocal (PR #68267)

[Matt Arsenault via cfe-commits]

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@@ -0,0 +1,130 @@
+// RUN: %clang_cc1 -O3 -triple %itanium_abi_triple -emit-llvm -o - %s | FileCheck -check-prefixes=CHECK,DEFAULT %s
+// RUN: %clang_cc1 -O3 -triple %itanium_abi_triple -freciprocal-math -emit-llvm -o - %s | FileCheck -check-prefixes=CHECK,FLAG %s
+
+float base(float a, float b, float c) {
+// CHECK-LABEL: _Z4basefff
+// FLAG: %[[A:.+]] = fdiv arcp float %b, %c
+// FLAG: %[[M:.+]] = fdiv arcp float %[[A]], %b
+// FLAG-NEXT: fadd arcp float %[[M]], %c
+
+// DEFAULT: %[[A:.+]] = fdiv float %b, %c
+// DEFAULT: %[[M:.+]] = fdiv float %[[A]], %b
+// DEFAULT-NEXT: fadd float %[[M]], %c
+  a = b / c;
+  return a / b + c;
+}
+
+// Simple case
+float fp_recip_simple(float a, float b, float c) {
+// CHECK-LABEL: _Z15fp_recip_simplefff
+// CHECK: %[[A:.+]] = fdiv arcp float %b, %c
+// CHECK: %[[M:.+]] = fdiv arcp float %[[A]], %b
+// CHECK-NEXT: fadd arcp float %[[M]], %c
+#pragma clang fp reciprocal(on)
+  a = b / c;
+  return a / b + c;
+}
+
+// Test interaction with -freciprocal-math
+float fp_recip_disable(float a, float b, float c) {
+// CHECK-LABEL: _Z16fp_recip_disablefff
+// CHECK: %[[A:.+]] = fdiv float %b, %c
+// CHECK: %[[M:.+]] = fdiv float %[[A]], %b
+// CHECK-NEXT: fadd float %[[M]], %c
+#pragma clang fp reciprocal(off)
+  a = b / c;
+  return a / b + c;
+}
+
+float fp_recip_with_reassoc_simple(float a, float b, float c) {
+// CHECK-LABEL: _Z28fp_recip_with_reassoc_simplefff
+// CHECK: %[[A:.+]] = fmul reassoc arcp float %b, %c
+// CHECK: %[[M:.+]] = fdiv reassoc arcp float %b, %[[A]]
+// CHECK-NEXT: fadd reassoc arcp float %[[M]], %c
+#pragma clang fp reciprocal(on) reassociate(on)
+  a = b / c;
+  return a / b + c;
+}
+
+// arcp pragma should only apply to its scope
+float fp_recip_scoped(float a, float b, float c) {
+  // CHECK-LABEL: _Z15fp_recip_scopedfff
+  // DEFAULT: %[[M:.+]] = fdiv float %a, %b
+  // DEFAULT-NEXT: fadd float %[[M]], %c
+  // FLAG: %[[M:.+]] = fdiv arcp float %a, %b
+  // FLAG-NEXT: fadd arcp float %[[M]], %c
+  {
+#pragma clang fp reciprocal(on)
+  }
+  return a / b + c;
+}
+
+// arcp pragma should apply to templates as well
+class Foo {};
+Foo operator+(Foo, Foo);
+template <typename T>
+T template_recip(T a, T b, T c) {
+#pragma clang fp reciprocal(on)
+  return ((a / b) - c) + c;
+}
+
+float fp_recip_template(float a, float b, float c) {
+  // CHECK-LABEL: _Z17fp_recip_templatefff
+  // CHECK: %[[A1:.+]] = fdiv arcp float %a, %b
+  // CHECK-NEXT: %[[A2:.+]] = fsub arcp float %[[A1]], %c
+  // CHECK-NEXT: fadd arcp float %[[A2]], %c
+  return template_recip<float>(a, b, c);
+}
+
+// File Scoping should work across functions
+#pragma clang fp reciprocal(on)
+float fp_file_scope_on(float a, float b, float c) {
+  // CHECK-LABEL: _Z16fp_file_scope_onfff
+  // CHECK: %[[M1:.+]] = fdiv arcp float %a, %c
+  // CHECK-NEXT: %[[M2:.+]] = fdiv arcp float %b, %c
+  // CHECK-NEXT: fadd arcp float %[[M1]], %[[M2]]
+  return (a / c) + (b / c);
+}
+
+// Inner pragma has precedence
+float fp_file_scope_stop(float a, float b, float c) {
+  // CHECK-LABEL: _Z18fp_file_scope_stopfff
+  // CHECK: %[[A:.+]] = fdiv arcp float %a, %a
+  // CHECK: %[[M1:.+]] = fdiv float %[[A]], %c
+  // CHECK-NEXT: %[[M2:.+]] = fdiv float %b, %c
+  // CHECK-NEXT: fsub float %[[M1]], %[[M2]]
+  a = a / a;
+  {
+#pragma clang fp reciprocal(off)
+    return (a / c) - (b / c);
+  }
+}
+
+#pragma clang fp reciprocal(off)
+float fp_recip_off(float a, float b, float c) {
+  // CHECK-LABEL: _Z12fp_recip_offfff
+  // CHECK: %[[D1:.+]] = fdiv float %a, %c
+  // CHECK-NEXT: %[[D2:.+]] = fdiv float %b, %c
+  // CHECK-NEXT: fadd float %[[D1]], %[[D2]]
+  return (a / c) + (b / c);
+}
+
+// Takes latest flag
+float fp_recip_many(float a, float b, float c) {
+// CHECK-LABEL: _Z13fp_recip_manyfff
+// CHECK: %[[D1:.+]] = fdiv arcp float %a, %c
+// CHECK-NEXT: %[[D2:.+]] = fdiv arcp float %b, %c
+// CHECK-NEXT: fadd arcp float %[[D1]], %[[D2]]
+#pragma clang fp reciprocal(off) reciprocal(on)
+  return (a / c) + (b / c);
+}
+
+// Pragma does not propagate through called functions
+float helper_func(float a, float b, float c) { return a + b + c; }
+float fp_recip_call_helper(float a, float b, float c) {
+// CHECK-LABEL: _Z20fp_recip_call_helperfff
+// CHECK: %[[S1:.+]] = fadd float %a, %b
+// CHECK-NEXT: fadd float %[[S1]], %c
+#pragma clang fp reciprocal(on)
+  return helper_func(a, b, c);
+}
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arsenm wrote:

That's already here on line 44 

https://github.com/llvm/llvm-project/pull/68267