[turbofan] First step towards correctified 64-bit addressing.

src/compiler/instruction.h

Index: src/compiler/instruction.h
diff --git a/src/compiler/instruction.h b/src/compiler/instruction.h
index 6d37b9f6932eec59d0c78e8db3db8687c137f0cb..75c3e9e34b0f94c0f1fc6fbe51e8d9727c2df756 100644
--- a/src/compiler/instruction.h
+++ b/src/compiler/instruction.h
@@ -675,8 +675,10 @@ class Constant FINAL {
   Type type() const { return type_; }
 
   int32_t ToInt32() const {
-    DCHECK_EQ(kInt32, type());
-    return static_cast<int32_t>(value_);
+    DCHECK(type() == kInt32 || type() == kInt64);
+    const int32_t value = static_cast<int32_t>(value_);
+    DCHECK_EQ(value_, static_cast<int64_t>(value));
+    return value;
   }
 
   int64_t ToInt64() const {