Subzero. Native 64-bit int arithmetic on x86-64.

src/IceInstX86Base.h

Index: src/IceInstX86Base.h
diff --git a/src/IceInstX86Base.h b/src/IceInstX86Base.h
index 4cfcfd4ea90b9498986e707cb20643098354b6d8..a57beef5d1bb367aedac1d343747b5b45baff8d0 100644
--- a/src/IceInstX86Base.h
+++ b/src/IceInstX86Base.h
@@ -1095,6 +1095,8 @@ class InstX86Movsx
     : public InstX86BaseUnaryopGPR<Machine, InstX86Base<Machine>::Movsx> {
 public:
   static InstX86Movsx *create(Cfg *Func, Variable *Dest, Operand *Src) {
+    assert(typeWidthInBytes(Dest->getType()) >
+           typeWidthInBytes(Src->getType()));
     return new (Func->allocate<InstX86Movsx>()) InstX86Movsx(Func, Dest, Src);
   }
 
@@ -1111,6 +1113,8 @@ class InstX86Movzx
     : public InstX86BaseUnaryopGPR<Machine, InstX86Base<Machine>::Movzx> {
 public:
   static InstX86Movzx *create(Cfg *Func, Variable *Dest, Operand *Src) {
+    assert(typeWidthInBytes(Dest->getType()) >
+           typeWidthInBytes(Src->getType()));
     return new (Func->allocate<InstX86Movzx>()) InstX86Movzx(Func, Dest, Src);
   }