[clang] Enable FPContract with optnone (#91061)

Previously treatment of the attribute `optnone` was modified in
#85605 ([clang] Set correct
FPOptions if attribute 'optnone' presents). As a side effect FPContract
was disabled for optnone. It created unneeded divergence with the
behavior of -O0, which enables this optimization.

In the discussion
#85605 (comment)
it was pointed out that FP contraction should be enabled even if all
optimizations are turned off, otherwise results of calculations would be
different. This change enables FPContract at optnone.

Author: spavloff

clang/include/clang/Basic/LangOptions.h

@@ -968,10 +968,7 @@ class FPOptionsOverride {
       setAllowFPContractAcrossStatement();
   }
 
-  void setDisallowOptimizations() {
-    setFPPreciseEnabled(true);
-    setDisallowFPContract();
-  }
+  void setDisallowOptimizations() { setFPPreciseEnabled(true); }
 
   storage_type getAsOpaqueInt() const {
     return (static_cast<storage_type>(Options.getAsOpaqueInt())

clang/test/AST/ast-dump-fpfeatures.cpp

@@ -198,7 +198,7 @@ float func_19(float x, float y) {
 // CHECK-LABEL: FunctionDecl {{.*}} func_19 'float (float, float)'
 // CHECK:         CompoundStmt {{.*}} MathErrno=1
 // CHECK:           ReturnStmt
-// CHECK:             BinaryOperator {{.*}} 'float' '+' ConstRoundingMode=downward MathErrno=1
+// CHECK:             BinaryOperator {{.*}} 'float' '+' FPContractMode=1 ConstRoundingMode=downward MathErrno=1
 
 __attribute__((optnone))
 float func_20(float x, float y) try {
@@ -210,7 +210,7 @@ float func_20(float x, float y) try {
 // CHECK-LABEL: FunctionDecl {{.*}} func_20 'float (float, float)'
 // CHECK:         CompoundStmt {{.*}} ConstRoundingMode=downward MathErrno=1
 // CHECK:           ReturnStmt
-// CHECK:             BinaryOperator {{.*}} 'float' '+' ConstRoundingMode=downward MathErrno=1
+// CHECK:             BinaryOperator {{.*}} 'float' '+' FPContractMode=1 ConstRoundingMode=downward MathErrno=1
 
 struct C21 {
   C21(float x, float y);
@@ -221,15 +221,15 @@ struct C21 {
 };
 
 // CHECK-LABEL: CXXMethodDecl {{.*}} a_method 'float (float, float)'
-// CHECK:         CompoundStmt {{.*}} ConstRoundingMode=downward MathErrno=1
+// CHECK:         CompoundStmt {{.*}} FPContractMode=1 ConstRoundingMode=downward MathErrno=1
 // CHECK:           ReturnStmt
-// CHECK:             BinaryOperator {{.*}} 'float' '*' ConstRoundingMode=downward MathErrno=1
+// CHECK:             BinaryOperator {{.*}} 'float' '*' FPContractMode=1 ConstRoundingMode=downward MathErrno=1
 
 __attribute__((optnone)) C21::C21(float x, float y) : member(x + y) {}
 
 // CHECK-LABEL: CXXConstructorDecl {{.*}} C21 'void (float, float)'
 // CHECK:         CXXCtorInitializer {{.*}} 'member' 'float'
-// CHECK:           BinaryOperator {{.*}} 'float' '+' ConstRoundingMode=downward MathErrno=1
+// CHECK:           BinaryOperator {{.*}} 'float' '+' FPContractMode=1 ConstRoundingMode=downward MathErrno=1
 
 template <typename T>
 __attribute__((optnone)) T func_22(T x, T y) {
@@ -238,13 +238,13 @@ __attribute__((optnone)) T func_22(T x, T y) {
 
 // CHECK-LABEL: FunctionTemplateDecl {{.*}} func_22
 // CHECK:         FunctionDecl {{.*}} func_22 'T (T, T)'
-// CHECK:           CompoundStmt {{.*}} ConstRoundingMode=downward MathErrno=1
+// CHECK:           CompoundStmt {{.*}} FPContractMode=1 ConstRoundingMode=downward MathErrno=1
 // CHECK:             ReturnStmt
-// CHECK:               BinaryOperator {{.*}} '+' ConstRoundingMode=downward MathErrno=1
+// CHECK:               BinaryOperator {{.*}} '+' FPContractMode=1 ConstRoundingMode=downward MathErrno=1
 // CHECK:         FunctionDecl {{.*}} func_22 'float (float, float)'
-// CHECK:           CompoundStmt {{.*}} ConstRoundingMode=downward MathErrno=1
+// CHECK:           CompoundStmt {{.*}} FPContractMode=1 ConstRoundingMode=downward MathErrno=1
 // CHECK:             ReturnStmt
-// CHECK:               BinaryOperator {{.*}} 'float' '+' ConstRoundingMode=downward MathErrno=1
+// CHECK:               BinaryOperator {{.*}} 'float' '+' FPContractMode=1 ConstRoundingMode=downward MathErrno=1
 
 float func_23(float x, float y) {
   return func_22(x, y);

clang/test/AST/ast-dump-fpfeatures.m

@@ -24,6 +24,6 @@ - (float) sum: (float)x with: (float)y __attribute((optnone)) {
 
 // CHECK-LABEL: ObjCImplementationDecl {{.*}} Adder
 // CHECK:         ObjCMethodDecl {{.*}} - sum:with: 'float'
-// CHECK:           CompoundStmt {{.*}} MathErrno=1
+// CHECK:           CompoundStmt {{.*}} FPContractMode=1 MathErrno=1
 // CHECK-NEXT:        ReturnStmt
-// CHECK-NEXT:          BinaryOperator {{.*}} 'float' '+' MathErrno=1
+// CHECK-NEXT:          BinaryOperator {{.*}} 'float' '+' FPContractMode=1 MathErrno=1

clang/test/AST/ast-dump-late-parsing.cpp

@@ -11,13 +11,13 @@ __attribute__((optnone)) T func_22(T x, T y) {
 
 // CHECK-LABEL: FunctionTemplateDecl {{.*}} func_22
 // CHECK:         FunctionDecl {{.*}} func_22 'T (T, T)'
-// CHECK:           CompoundStmt {{.*}} ConstRoundingMode=downward MathErrno=1
+// CHECK:           CompoundStmt {{.*}} FPContractMode=1 ConstRoundingMode=downward MathErrno=1
 // CHECK:             ReturnStmt
-// CHECK:               BinaryOperator {{.*}} '+' ConstRoundingMode=downward MathErrno=1
+// CHECK:               BinaryOperator {{.*}} '+' FPContractMode=1 ConstRoundingMode=downward MathErrno=1
 // CHECK:         FunctionDecl {{.*}} func_22 'float (float, float)'
-// CHECK:           CompoundStmt {{.*}} ConstRoundingMode=downward MathErrno=1
+// CHECK:           CompoundStmt {{.*}} FPContractMode=1 ConstRoundingMode=downward MathErrno=1
 // CHECK:             ReturnStmt
-// CHECK:               BinaryOperator {{.*}} 'float' '+' ConstRoundingMode=downward MathErrno=1
+// CHECK:               BinaryOperator {{.*}} 'float' '+' FPContractMode=1 ConstRoundingMode=downward MathErrno=1
 
 float func_23(float x, float y) {
   return func_22(x, y);