[Hexagon] Add inline-asm constraint 'a' for modifier register class

For example
  asm ("memw(%0++%1) = %2" : : "r"(addr),"a"(mod),"r"(val) : "memory")

llvm-svn: 308763

clang/lib/Basic/Targets.cpp

@@ -6887,6 +6887,9 @@ public:
           return true;
         }
         break;
+      case 'a': // Modifier register m0-m1.
+        Info.setAllowsRegister();
+        return true;
       case 's':
         // Relocatable constant.
         return true;

clang/test/CodeGen/hexagon-inline-asm.c

@@ -15,3 +15,9 @@ void foo(v64 v0, v64 v1, v64 *p) {
   asm ("%0 = memw(##%1)" : "=r"(r) : "s"(&g));
 // CHECK: call i32 asm "$0 = memw(##$1)", "=r,s"(i32* @g)
 }
+
+void fred(unsigned *p, unsigned m, unsigned v) {
+  asm ("memw(%0++%1) = %2" : : "r"(p),"a"(m),"r"(v) : "memory");
+// CHECK: call void asm sideeffect "memw($0++$1) = $2", "r,a,r,~{memory}"(i32* %0, i32 %1, i32 %2)
+}
+