1 files changed, 7 insertions, 0 deletions
diff --git a/llvm/lib/CodeGen/GlobalISel/Utils.cpp b/llvm/lib/CodeGen/GlobalISel/Utils.cpp
index f39b38779bc..f5b97656c3b 100644
--- a/llvm/lib/CodeGen/GlobalISel/Utils.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/Utils.cpp
@@ -58,6 +58,13 @@ unsigned llvm::constrainOperandRegClass(
   // register class constraints on some of their operands: If it's a use, we can
   // skip constraining as the instruction defining the register would constrain
   // it.
+
+  // We can't constrain unallocatable register classes, because we can't create
+  // virtual registers for these classes, so we need to let targets handled this
+  // case.
+  if (RegClass && !RegClass->isAllocatable())
+    RegClass = TRI.getConstrainedRegClassForOperand(RegMO, MRI);
+
   if (!RegClass) {
     assert((!isTargetSpecificOpcode(II.getOpcode()) || RegMO.isUse()) &&
            "Register class constraint is required unless either the "