Fix handling of the 'n' asm constraint with invalid operands.

[jyknight]

Summary

It had accidently accepted a symbol+offset value (and emitted
incorrect code for it, keeping only the offset part) instead of
properly reporting the constraint as invalid.

[echristo]

LGTM.

-eric

lib/CodeGen/SelectionDAG/TargetLowering.cpp

case 's': {  // Relocatable Constant
     // value itself doesn't get selected.
     if (GA) {   // Either &GV   or   &GV+C
       if (ConstraintLetter != 'n') {
         int64_t Offs = GA->getOffset();
         if (C) Offs += C->getZExtValue();
         Ops.push_back(DAG.getTargetGlobalAddress(GA->getGlobal(),
                                                  C ? SDLoc(C) : SDLoc(),
                                                  Op.getValueType(), Offs));
-        return;
       }
+      return;
     }
     if (C) {   // just C, no GV.
       // Simple constants are not allowed for 's'.
       if (ConstraintLetter != 's') {
         // gcc prints these as sign extended.  Sign extend value to 64 bits
         // now; without this it would get ZExt'd later in
         // ScheduleDAGSDNodes::EmitNode, which is very generic.
         Ops.push_back(DAG.getTargetConstant(C->getAPIntValue().getSExtValue(),
                                             SDLoc(C), MVT::i64));
-        return;
       }
+      return;
     }
     break;
   }
   }
 }
 
 std::pair<unsigned, const TargetRegisterClass *>
 TargetLowering::getRegForInlineAsmConstraint(const TargetRegisterInfo *RI,

test/CodeGen/X86/inline-asm-bad-constraint-n.ll

+; RUN: not llc -march=x86 -no-integrated-as < %s 2>&1 | FileCheck %s
+
+@x = global i32 0, align 4
+
+;CHECK: error: invalid operand for inline asm constraint 'n'
+define void @foo() {
+  %a = getelementptr i32, i32* @x, i32 1
+  call void asm sideeffect "foo $0", "n"(i32* %a) nounwind
+  ret void
+}