GH-100222: Redefine _Py_CODEUNIT as a union to clarify structure of code unit. (GH-100223)

1 files changed, 17 insertions, 14 deletions

diff --git a/Include/cpython/code.h b/Include/cpython/code.h
index fc7c5ed..6a13ff2 100644
--- a/Include/cpython/code.h
+++ b/Include/cpython/code.h
@@ -16,21 +16,24 @@ extern "C" {
  * 2**32 - 1, rather than INT_MAX.
  */
 
-typedef uint16_t _Py_CODEUNIT;
-
-#ifdef WORDS_BIGENDIAN
-#  define _Py_OPCODE(word) ((word) >> 8)
-#  define _Py_OPARG(word) ((word) & 255)
-#  define _Py_MAKECODEUNIT(opcode, oparg) (((opcode)<<8)|(oparg))
-#else
-#  define _Py_OPCODE(word) ((word) & 255)
-#  define _Py_OPARG(word) ((word) >> 8)
-#  define _Py_MAKECODEUNIT(opcode, oparg) ((opcode)|((oparg)<<8))
-#endif
+typedef union {
+    uint16_t cache;
+    struct {
+        uint8_t opcode;
+        uint8_t oparg;
+    };
+} _Py_CODEUNIT;
+
+#define _Py_OPCODE(word) ((word).opcode)
+#define _Py_OPARG(word) ((word).oparg)
+
+static inline void
+_py_set_opocde(_Py_CODEUNIT *word, uint8_t opcode)
+{
+    word->opcode = opcode;
+}
 
-// Use "unsigned char" instead of "uint8_t" here to avoid illegal aliasing:
-#define _Py_SET_OPCODE(word, opcode) \
-    do { ((unsigned char *)&(word))[0] = (opcode); } while (0)
+#define _Py_SET_OPCODE(word, opcode) _py_set_opocde(&(word), opcode)
 
 typedef struct {
     PyObject *_co_code;