[flang] Modifications to ieee_support_standard

Some Arm processors support exception halting control and some do not.
An Arm executable will run on either type of processor, so it is effectively
unknown at compile time whether or not this support will be available.
ieee_support_halting is therefore implemented with a runtime check.

The result of a call to ieee_support_standard depends in part on support
for halting control. Update the ieee_support_standard implementation to
check for support for halting control at runtime.

Author: vdonaldson

flang/docs/Extensions.md

@@ -150,13 +150,15 @@ end
   have this capability. An Arm executable will run on either type of
   processor, so it is effectively unknown at compile time whether or
   not this support will be available at runtime. The standard requires
-  that a call to intrinsic module procedure `IEEE_SUPPORT_HALTING` with
+  that a call to intrinsic module procedure `ieee_support_halting` with
   a constant argument has a compile time constant result in `constant
   expression` and `specification expression` contexts. In compilations
   where this information is not known at compile time, f18 generates code
   to determine the absence or presence of this capability at runtime.
-  A call to `IEEE_SUPPORT_HALTING` in contexts that the standard requires
-  to be constant will generate a compilation error.
+  A call to `ieee_support_halting` in contexts that the standard requires
+  to be constant will generate a compilation error. `ieee_support_standard`
+  depends in part on `ieee_support_halting`, so this also applies to
+  `ieee_support_standard` calls.
 
 ## Extensions, deletions, and legacy features supported by default
 

flang/include/flang/Optimizer/Builder/IntrinsicCall.h

@@ -314,6 +314,8 @@ struct IntrinsicLibrary {
   fir::ExtendedValue genIeeeSupportHalting(mlir::Type,
                                            llvm::ArrayRef<fir::ExtendedValue>);
   mlir::Value genIeeeSupportRounding(mlir::Type, llvm::ArrayRef<mlir::Value>);
+  fir::ExtendedValue genIeeeSupportStandard(mlir::Type,
+                                            llvm::ArrayRef<fir::ExtendedValue>);
   template <mlir::arith::CmpIPredicate pred>
   mlir::Value genIeeeTypeCompare(mlir::Type, llvm::ArrayRef<mlir::Value>);
   mlir::Value genIeeeUnordered(mlir::Type, llvm::ArrayRef<mlir::Value>);

flang/lib/Evaluate/fold-logical.cpp

@@ -882,7 +882,7 @@ Expr<Type<TypeCategory::Logical, KIND>> FoldIntrinsicFunction(
         IeeeFeature::Flags)};
   } else if (name == "__builtin_ieee_support_halting") {
     if (!context.targetCharacteristics()
-             .haltingSupportIsUnknownAtCompileTime()) {
+            .haltingSupportIsUnknownAtCompileTime()) {
       return Expr<T>{context.targetCharacteristics().ieeeFeatures().test(
           IeeeFeature::Halting)};
     }
@@ -906,8 +906,12 @@ Expr<Type<TypeCategory::Logical, KIND>> FoldIntrinsicFunction(
     return Expr<T>{
         context.targetCharacteristics().ieeeFeatures().test(IeeeFeature::Sqrt)};
   } else if (name == "__builtin_ieee_support_standard") {
-    return Expr<T>{context.targetCharacteristics().ieeeFeatures().test(
-        IeeeFeature::Standard)};
+    // ieee_support_standard depends in part on ieee_support_halting.
+    if (!context.targetCharacteristics()
+            .haltingSupportIsUnknownAtCompileTime()) {
+      return Expr<T>{context.targetCharacteristics().ieeeFeatures().test(
+          IeeeFeature::Standard)};
+    }
   } else if (name == "__builtin_ieee_support_subnormal") {
     return Expr<T>{context.targetCharacteristics().ieeeFeatures().test(
         IeeeFeature::Subnormal)};

flang/lib/Optimizer/Builder/IntrinsicCall.cpp

@@ -458,6 +458,7 @@ static constexpr IntrinsicHandler handlers[]{
      /*isElemental=*/false},
     {"ieee_support_halting", &I::genIeeeSupportHalting},
     {"ieee_support_rounding", &I::genIeeeSupportRounding},
+    {"ieee_support_standard", &I::genIeeeSupportStandard},
     {"ieee_unordered", &I::genIeeeUnordered},
     {"ieee_value", &I::genIeeeValue},
     {"ieor", &I::genIeor},
@@ -5671,6 +5672,19 @@ IntrinsicLibrary::genIeeeSupportRounding(mlir::Type resultType,
       loc, resultType, builder.create<mlir::arith::AndIOp>(loc, lbOk, ubOk));
 }
 
+// IEEE_SUPPORT_STANDARD
+fir::ExtendedValue IntrinsicLibrary::genIeeeSupportStandard(
+    mlir::Type resultType, llvm::ArrayRef<fir::ExtendedValue> args) {
+  // Check if IEEE standard support is available, which reduces to checking
+  // if halting control is supported, as that is the only support component
+  // that may not be available.
+  assert(args.size() <= 1);
+  mlir::Value nearest = builder.createIntegerConstant(
+      loc, builder.getIntegerType(32), _FORTRAN_RUNTIME_IEEE_NEAREST);
+  return builder.createConvert(
+      loc, resultType, fir::runtime::genSupportHalting(builder, loc, nearest));
+}
+
 // IEEE_UNORDERED
 mlir::Value
 IntrinsicLibrary::genIeeeUnordered(mlir::Type resultType,