Index: llvm/lib/Target/AMDGPU/SIISelLowering.cpp
===================================================================
--- llvm/lib/Target/AMDGPU/SIISelLowering.cpp
+++ llvm/lib/Target/AMDGPU/SIISelLowering.cpp
@@ -11744,18 +11744,19 @@
       return std::make_pair(0U, RC);
   }
 
-  if (Constraint.size() > 1) {
-    if (Constraint[1] == 'v') {
+  if (Constraint.startswith("{") && Constraint.endswith("}")) {
+    StringRef RegName(Constraint.data() + 1, Constraint.size() - 2);
+    if (RegName[0] == 'v') {
       RC = &AMDGPU::VGPR_32RegClass;
-    } else if (Constraint[1] == 's') {
+    } else if (RegName[0] == 's') {
       RC = &AMDGPU::SGPR_32RegClass;
-    } else if (Constraint[1] == 'a') {
+    } else if (RegName[0] == 'a') {
       RC = &AMDGPU::AGPR_32RegClass;
     }
 
     if (RC) {
       uint32_t Idx;
-      bool Failed = Constraint.substr(2).getAsInteger(10, Idx);
+      bool Failed = RegName.substr(1).getAsInteger(10, Idx);
       if (!Failed && Idx < RC->getNumRegs())
         return std::make_pair(RC->getRegister(Idx), RC);
     }