[AMDGPU] Fix codegen for inline assembly

Need to override convertConstraint to recognise amdgpu specific register names.

Differential Revision: https://reviews.llvm.org/D44533

llvm-svn: 328359
diff --git a/clang/test/Sema/inline-asm-validate-amdgpu.cl b/clang/test/Sema/inline-asm-validate-amdgpu.cl
index bc2580c..51009ec 100644
--- a/clang/test/Sema/inline-asm-validate-amdgpu.cl
+++ b/clang/test/Sema/inline-asm-validate-amdgpu.cl
@@ -74,3 +74,8 @@
 
     c[i] = ci;
 }
+
+void test_long(int arg0) {
+  long v15_16;
+  __asm volatile("v_lshlrev_b64 v[15:16], 0, %0" : "={v[15:16]}"(v15_16) : "v"(arg0));
+}