Basic: [asmSymbolicName] follows the same rule as numbers in asm inputs

Input constraints like "0" and "[foo]" should be treated the same when
it comes to their corresponding output constraint.

This fixes PR21850.

llvm-svn: 225605

clang/lib/Basic/TargetInfo.cpp

@@ -583,6 +583,10 @@ bool TargetInfo::validateInputConstraint(ConstraintInfo *OutputConstraints,
       if (Info.hasTiedOperand() && Info.getTiedOperand() != Index)
         return false;
 
+      // A number must refer to an output only operand.
+      if (OutputConstraints[Index].isReadWrite())
+        return false;
+
       Info.setTiedOperand(Index, OutputConstraints[Index]);
       break;
     }

clang/test/Sema/asm.c

@@ -190,3 +190,10 @@ void fn4() {
           : "=r"(l)
           : "#m"(l)); // expected-error {{invalid input constraint '#m' in asm}}
 }
+
+void fn5() {
+  int l;
+    __asm__(""
+          : [g] "+r"(l)
+          : "[g]"(l)); // expected-error {{invalid input constraint '[g]' in asm}}
+}