[Sema] Allow conversion between long double and __float128.

We should only ban this if long double is a double double. x86's 80 bit
long double is fine and supported by the backend.

llvm-svn: 322779

clang/lib/Sema/SemaExpr.cpp

@@ -1092,13 +1092,12 @@ static bool unsupportedTypeConversion(const Sema &S, QualType LHSType,
   Float128AndLongDouble |= (LHSElemType == S.Context.LongDoubleTy &&
                             RHSElemType == S.Context.Float128Ty);
 
-  /* We've handled the situation where __float128 and long double have the same
-     representation. The only other allowable conversion is if long double is
-     really just double.
-  */
+  // We've handled the situation where __float128 and long double have the same
+  // representation. We allow all conversions for all possible long double types
+  // except PPC's double double.
   return Float128AndLongDouble &&
-    (&S.Context.getFloatTypeSemantics(S.Context.LongDoubleTy) !=
-     &llvm::APFloat::IEEEdouble());
+    (&S.Context.getFloatTypeSemantics(S.Context.LongDoubleTy) ==
+     &llvm::APFloat::PPCDoubleDouble());
 }
 
 typedef ExprResult PerformCastFn(Sema &S, Expr *operand, QualType toType);

clang/lib/Sema/SemaOverload.cpp

@@ -1764,8 +1764,8 @@ static bool IsStandardConversion(Sema &S, Expr* From, QualType ToType,
                                    (FromType == S.Context.LongDoubleTy &&
                                     ToType == S.Context.Float128Ty));
       if (Float128AndLongDouble &&
-          (&S.Context.getFloatTypeSemantics(S.Context.LongDoubleTy) !=
-           &llvm::APFloat::IEEEdouble()))
+          (&S.Context.getFloatTypeSemantics(S.Context.LongDoubleTy) ==
+           &llvm::APFloat::PPCDoubleDouble()))
         return false;
     }
     // Floating point conversions (C++ 4.8).

clang/test/Sema/float128-ld-incompatibility.cpp

@@ -1,10 +1,12 @@
 // RUN: %clang_cc1 -fsyntax-only -verify -std=c++11 \
 // RUN: -triple powerpc64le-unknown-linux-gnu -target-cpu pwr8 \
 // RUN: -target-feature +float128 %s
+// RUN: %clang_cc1 -fsyntax-only -std=c++11 -triple x86_64-unknown-linux-gnu -Wno-unused-value -Wno-parentheses %s
 
 __float128 qf();
 long double ldf();
 
+#ifdef __PPC__
 // FIXME: once operations between long double and __float128 are implemented for
 //        targets where the types are different, these next two will change
 long double ld{qf()}; // expected-error {{cannot initialize a variable of type 'long double' with an rvalue of type '__float128'}}
@@ -17,6 +19,7 @@ auto test1(__float128 q, long double ld) -> decltype(q + ld) { // expected-error
 auto test2(long double a, __float128 b) -> decltype(a + b) { // expected-error {{invalid operands to binary expression ('long double' and '__float128')}}
   return a + b;      // expected-error {{invalid operands to binary expression ('long double' and '__float128')}}
 }
+#endif
 
 void test3(bool b) {
   long double ld;