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

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Dec 14, 2022
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GH-100222: Redefine _Py_CODEUNIT as a union to clarify structure of code unit. #100223

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31 changes: 17 additions & 14 deletions Include/cpython/code.h
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
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Is the idea to later add more opargs here?

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Up to you.
I guess it depends on how you want to align the instructions.

16 bit alignment

typedef union {
    int16_t cache;
    struct {
         uint8_t opcode;
         uint8_t oparg0;
    };
    struct {
         uint8_t oparg1;
         uint8_t oparg2;
    };
} _Py_CODEUNIT;

32 bit alignment

typedef union {
    int32_t cache;
    struct {
         uint8_t opcode;
         uint8_t oparg0;
         uint8_t oparg1;
         uint8_t oparg2;
    };
} _Py_CODEUNIT;

};
} _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;
Expand Down
48 changes: 24 additions & 24 deletions Include/internal/pycore_code.h
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Expand Up @@ -18,53 +18,53 @@ extern "C" {
#define CACHE_ENTRIES(cache) (sizeof(cache)/sizeof(_Py_CODEUNIT))

typedef struct {
_Py_CODEUNIT counter;
_Py_CODEUNIT index;
_Py_CODEUNIT module_keys_version[2];
_Py_CODEUNIT builtin_keys_version;
uint16_t counter;
uint16_t index;
uint16_t module_keys_version[2];
uint16_t builtin_keys_version;
} _PyLoadGlobalCache;

#define INLINE_CACHE_ENTRIES_LOAD_GLOBAL CACHE_ENTRIES(_PyLoadGlobalCache)

typedef struct {
_Py_CODEUNIT counter;
uint16_t counter;
} _PyBinaryOpCache;

#define INLINE_CACHE_ENTRIES_BINARY_OP CACHE_ENTRIES(_PyBinaryOpCache)

typedef struct {
_Py_CODEUNIT counter;
uint16_t counter;
} _PyUnpackSequenceCache;

#define INLINE_CACHE_ENTRIES_UNPACK_SEQUENCE \
CACHE_ENTRIES(_PyUnpackSequenceCache)

typedef struct {
_Py_CODEUNIT counter;
_Py_CODEUNIT mask;
uint16_t counter;
uint16_t mask;
} _PyCompareOpCache;

#define INLINE_CACHE_ENTRIES_COMPARE_OP CACHE_ENTRIES(_PyCompareOpCache)

typedef struct {
_Py_CODEUNIT counter;
_Py_CODEUNIT type_version[2];
_Py_CODEUNIT func_version;
uint16_t counter;
uint16_t type_version[2];
uint16_t func_version;
} _PyBinarySubscrCache;

#define INLINE_CACHE_ENTRIES_BINARY_SUBSCR CACHE_ENTRIES(_PyBinarySubscrCache)

typedef struct {
_Py_CODEUNIT counter;
_Py_CODEUNIT version[2];
_Py_CODEUNIT index;
uint16_t counter;
uint16_t version[2];
uint16_t index;
} _PyAttrCache;

typedef struct {
_Py_CODEUNIT counter;
_Py_CODEUNIT type_version[2];
_Py_CODEUNIT keys_version[2];
_Py_CODEUNIT descr[4];
uint16_t counter;
uint16_t type_version[2];
uint16_t keys_version[2];
uint16_t descr[4];
} _PyLoadMethodCache;


Expand All @@ -74,21 +74,21 @@ typedef struct {
#define INLINE_CACHE_ENTRIES_STORE_ATTR CACHE_ENTRIES(_PyAttrCache)

typedef struct {
_Py_CODEUNIT counter;
_Py_CODEUNIT func_version[2];
_Py_CODEUNIT min_args;
uint16_t counter;
uint16_t func_version[2];
uint16_t min_args;
} _PyCallCache;

#define INLINE_CACHE_ENTRIES_CALL CACHE_ENTRIES(_PyCallCache)

typedef struct {
_Py_CODEUNIT counter;
uint16_t counter;
} _PyStoreSubscrCache;

#define INLINE_CACHE_ENTRIES_STORE_SUBSCR CACHE_ENTRIES(_PyStoreSubscrCache)

typedef struct {
_Py_CODEUNIT counter;
uint16_t counter;
} _PyForIterCache;

#define INLINE_CACHE_ENTRIES_FOR_ITER CACHE_ENTRIES(_PyForIterCache)
Expand Down Expand Up @@ -409,7 +409,7 @@ write_location_entry_start(uint8_t *ptr, int code, int length)
static inline uint16_t
adaptive_counter_bits(int value, int backoff) {
return (value << ADAPTIVE_BACKOFF_BITS) |
(backoff & ((1<<ADAPTIVE_BACKOFF_BITS)-1));
(backoff & ((1<<ADAPTIVE_BACKOFF_BITS)-1));
}

static inline uint16_t
Expand Down
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2022-12-13-16-05-18.gh-issue-100222.OVVvYe.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Redefine the ``_Py_CODEUNIT`` typedef as a union to describe its layout to
the C compiler, avoiding type punning and improving clarity.
11 changes: 6 additions & 5 deletions Objects/codeobject.c
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Expand Up @@ -1520,9 +1520,10 @@ deopt_code(_Py_CODEUNIT *instructions, Py_ssize_t len)
_Py_CODEUNIT instruction = instructions[i];
int opcode = _PyOpcode_Deopt[_Py_OPCODE(instruction)];
int caches = _PyOpcode_Caches[opcode];
instructions[i] = _Py_MAKECODEUNIT(opcode, _Py_OPARG(instruction));
instructions[i].opcode = opcode;
while (caches--) {
instructions[++i] = _Py_MAKECODEUNIT(CACHE, 0);
instructions[++i].opcode = CACHE;
instructions[i].oparg = 0;
}
}
}
Expand Down Expand Up @@ -1775,9 +1776,9 @@ code_richcompare(PyObject *self, PyObject *other, int op)
for (int i = 0; i < Py_SIZE(co); i++) {
_Py_CODEUNIT co_instr = _PyCode_CODE(co)[i];
_Py_CODEUNIT cp_instr = _PyCode_CODE(cp)[i];
_Py_SET_OPCODE(co_instr, _PyOpcode_Deopt[_Py_OPCODE(co_instr)]);
_Py_SET_OPCODE(cp_instr, _PyOpcode_Deopt[_Py_OPCODE(cp_instr)]);
eq = co_instr == cp_instr;
co_instr.opcode = _PyOpcode_Deopt[_Py_OPCODE(co_instr)];
cp_instr.opcode =_PyOpcode_Deopt[_Py_OPCODE(cp_instr)];
eq = co_instr.cache == cp_instr.cache;
if (!eq) {
goto unequal;
}
Expand Down
4 changes: 2 additions & 2 deletions Python/ceval.c
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Original file line number Diff line number Diff line change
Expand Up @@ -864,7 +864,7 @@ GETITEM(PyObject *v, Py_ssize_t i) {
STAT_INC(opcode, miss); \
STAT_INC((INSTNAME), miss); \
/* The counter is always the first cache entry: */ \
if (ADAPTIVE_COUNTER_IS_ZERO(*next_instr)) { \
if (ADAPTIVE_COUNTER_IS_ZERO(next_instr->cache)) { \
STAT_INC((INSTNAME), deopt); \
} \
else { \
Expand Down Expand Up @@ -1289,7 +1289,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
}
opcode = _PyOpcode_Deopt[opcode];
if (_PyOpcode_Caches[opcode]) {
_Py_CODEUNIT *counter = &next_instr[1];
uint16_t *counter = &next_instr[1].cache;
// The instruction is going to decrement the counter, so we need to
// increment it here to make sure it doesn't try to specialize:
if (!ADAPTIVE_COUNTER_IS_MAX(*counter)) {
Expand Down
20 changes: 15 additions & 5 deletions Python/compile.c
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Expand Up @@ -261,22 +261,32 @@ write_instr(_Py_CODEUNIT *codestr, struct instr *instruction, int ilen)
int caches = _PyOpcode_Caches[opcode];
switch (ilen - caches) {
case 4:
*codestr++ = _Py_MAKECODEUNIT(EXTENDED_ARG, (oparg >> 24) & 0xFF);
codestr->opcode = EXTENDED_ARG;
codestr->oparg = (oparg >> 24) & 0xFF;
codestr++;
/* fall through */
case 3:
*codestr++ = _Py_MAKECODEUNIT(EXTENDED_ARG, (oparg >> 16) & 0xFF);
codestr->opcode = EXTENDED_ARG;
codestr->oparg = (oparg >> 16) & 0xFF;
codestr++;
/* fall through */
case 2:
*codestr++ = _Py_MAKECODEUNIT(EXTENDED_ARG, (oparg >> 8) & 0xFF);
codestr->opcode = EXTENDED_ARG;
codestr->oparg = (oparg >> 8) & 0xFF;
codestr++;
/* fall through */
case 1:
*codestr++ = _Py_MAKECODEUNIT(opcode, oparg & 0xFF);
codestr->opcode = opcode;
codestr->oparg = oparg & 0xFF;
codestr++;
break;
default:
Py_UNREACHABLE();
}
while (caches--) {
*codestr++ = _Py_MAKECODEUNIT(CACHE, 0);
codestr->opcode = CACHE;
codestr->oparg = 0;
codestr++;
}
}

Expand Down
26 changes: 13 additions & 13 deletions Python/generated_cases.c.h
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