Add option to force filetype=asm for testing

src/IceTargetLoweringX8632Traits.h

Index: src/IceTargetLoweringX8632Traits.h
diff --git a/src/IceTargetLoweringX8632Traits.h b/src/IceTargetLoweringX8632Traits.h
index 00ea2d91cce1de6df2b2c935b27d5e3c9af07b77..ab22bfdbe16c36b364a88897bbe26df600625b4f 100644
--- a/src/IceTargetLoweringX8632Traits.h
+++ b/src/IceTargetLoweringX8632Traits.h
@@ -364,8 +364,19 @@ struct TargetX8632Traits {
     assert(RegNum != Variable::NoRegister);
     // TODO(stichnot): Rewrite this as a table lookup from a table computed in a
     // TargetLowering static initializer.
+    // [abcd]h registers are not convertible to their ?l, ?x, and e?x versions.
+    switch (RegNum) {
+    default:
+      break;
+    case RegisterSet::Reg_ah:
+    case RegisterSet::Reg_bh:
+    case RegisterSet::Reg_ch:
+    case RegisterSet::Reg_dh:
+      assert(isByteSizedType(Ty));
+      return RegNum;
+    }
     RegNum = getBaseReg(RegNum);
-    if (Ty == IceType_i8 || Ty == IceType_i1) {
+    if (isByteSizedType(Ty)) {
       switch (RegNum) {
       default:
         assert(0);