peephole.c

/* Peephole optimizations for bytecode compiler. */

#include "Python.h"

#include "Python-ast.h"
#include "node.h"
#include "ast.h"
#include "code.h"
#include "symtable.h"
#include "opcode.h"

#define UNCONDITIONAL_JUMP(op)  (op==JUMP_ABSOLUTE || op==JUMP_FORWARD)
#define CONDITIONAL_JUMP(op) (op==POP_JUMP_IF_FALSE || op==POP_JUMP_IF_TRUE \
    || op==JUMP_IF_FALSE_OR_POP || op==JUMP_IF_TRUE_OR_POP)
#define ABSOLUTE_JUMP(op) (op==JUMP_ABSOLUTE \
    || op==POP_JUMP_IF_FALSE || op==POP_JUMP_IF_TRUE \
    || op==JUMP_IF_FALSE_OR_POP || op==JUMP_IF_TRUE_OR_POP || op==JUMP_IF_NOT_EXC_MATCH)
#define JUMPS_ON_TRUE(op) (op==POP_JUMP_IF_TRUE || op==JUMP_IF_TRUE_OR_POP)
#define GETJUMPTGT(arr, i) (get_arg(arr, i) / sizeof(_Py_CODEUNIT) + \
        (ABSOLUTE_JUMP(_Py_OPCODE(arr[i])) ? 0 : i+1))
#define ISBASICBLOCK(blocks, start, end) \
    (blocks[start]==blocks[end])


// /* Scans back N consecutive LOAD_CONST instructions, skipping NOPs,
//    returns index of the Nth last's LOAD_CONST's EXTENDED_ARG prefix.
//    Callers are responsible to check CONST_STACK_LEN beforehand.
// */
// static Py_ssize_t
// lastn_const_start(const _Py_CODEUNIT *codestr, Py_ssize_t i, Py_ssize_t n)
// {
//     assert(n > 0);
//     for (;;) {
//         i--;
//         assert(i >= 0);
//         if (_Py_OPCODE(codestr[i]) == LOAD_CONST) {
//             if (!--n) {
//                 while (i > 0 && _Py_OPCODE(codestr[i-1]) == EXTENDED_ARG) {
//                     i--;
//                 }
//                 return i;
//             }
//         }
//         else {
//             assert(_Py_OPCODE(codestr[i]) == EXTENDED_ARG);
//         }
//     }
// }

// /* Scans through EXTENDED ARGs, seeking the index of the effective opcode */
// static Py_ssize_t
// find_op(const _Py_CODEUNIT *codestr, Py_ssize_t codelen, Py_ssize_t i)
// {
//     while (i < codelen && _Py_OPCODE(codestr[i]) == EXTENDED_ARG) {
//         i++;
//     }
//     return i;
// }

// /* Given the index of the effective opcode,
//    scan back to construct the oparg with EXTENDED_ARG */
// static unsigned int
// get_arg(const _Py_CODEUNIT *codestr, Py_ssize_t i)
// {
//     _Py_CODEUNIT word;
//     unsigned int oparg = _Py_OPARG(codestr[i]);
//     if (i >= 1 && _Py_OPCODE(word = codestr[i-1]) == EXTENDED_ARG) {
//         oparg |= _Py_OPARG(word) << 8;
//         if (i >= 2 && _Py_OPCODE(word = codestr[i-2]) == EXTENDED_ARG) {
//             oparg |= _Py_OPARG(word) << 16;
//             if (i >= 3 && _Py_OPCODE(word = codestr[i-3]) == EXTENDED_ARG) {
//                 oparg |= _Py_OPARG(word) << 24;
//             }
//         }
//     }
//     return oparg;
// }

// /* Fill the region with NOPs. */
// static void
// fill_nops(_Py_CODEUNIT *codestr, Py_ssize_t start, Py_ssize_t end)
// {
//     memset(codestr + start, NOP, (end - start) * sizeof(_Py_CODEUNIT));
// }

// /* Given the index of the effective opcode,
//    attempt to replace the argument, taking into account EXTENDED_ARG.
//    Returns -1 on failure, or the new op index on success */
// static Py_ssize_t
// set_arg(_Py_CODEUNIT *codestr, Py_ssize_t i, unsigned int oparg)
// {
//     unsigned int curarg = get_arg(codestr, i);
//     int curilen, newilen;
//     if (curarg == oparg)
//         return i;
//     curilen = instrsize(curarg);
//     newilen = instrsize(oparg);
//     if (curilen < newilen) {
//         return -1;
//     }

//     write_op_arg(codestr + i + 1 - curilen, _Py_OPCODE(codestr[i]), oparg, newilen);
//     fill_nops(codestr, i + 1 - curilen + newilen, i + 1);
//     return i-curilen+newilen;
// }

// /* Attempt to write op/arg at end of specified region of memory.
//    Preceding memory in the region is overwritten with NOPs.
//    Returns -1 on failure, op index on success */
// static Py_ssize_t
// copy_op_arg(_Py_CODEUNIT *codestr, Py_ssize_t i, unsigned char op,
//             unsigned int oparg, Py_ssize_t maxi)
// {
//     int ilen = instrsize(oparg);
//     if (i + ilen > maxi) {
//         return -1;
//     }
//     write_op_arg(codestr + maxi - ilen, op, oparg, ilen);
//     fill_nops(codestr, i, maxi - ilen);
//     return maxi - 1;
// }

// /* Replace LOAD_CONST c1, LOAD_CONST c2 ... LOAD_CONST cn, BUILD_TUPLE n
//    with    LOAD_CONST (c1, c2, ... cn).
//    The consts table must still be in list form so that the
//    new constant (c1, c2, ... cn) can be appended.
//    Called with codestr pointing to the first LOAD_CONST.
// */
// static Py_ssize_t
// fold_tuple_on_constants(_Py_CODEUNIT *codestr, Py_ssize_t codelen,
//                         Py_ssize_t c_start, Py_ssize_t opcode_end,
//                         PyObject *consts, int n)
// {
//     /* Pre-conditions */
//     assert(PyList_CheckExact(consts));

//     /* Buildup new tuple of constants */
//     PyObject *newconst = PyTuple_New(n);
//     if (newconst == NULL) {
//         return -1;
//     }

//     for (Py_ssize_t i = 0, pos = c_start; i < n; i++, pos++) {
//         assert(pos < opcode_end);
//         pos = find_op(codestr, codelen, pos);
//         assert(_Py_OPCODE(codestr[pos]) == LOAD_CONST);

//         unsigned int arg = get_arg(codestr, pos);
//         PyObject *constant = PyList_GET_ITEM(consts, arg);
//         Py_INCREF(constant);
//         PyTuple_SET_ITEM(newconst, i, constant);
//     }

//     Py_ssize_t index = PyList_GET_SIZE(consts);
// #if SIZEOF_SIZE_T > SIZEOF_INT
//     if ((size_t)index >= UINT_MAX - 1) {
//         Py_DECREF(newconst);
//         PyErr_SetString(PyExc_OverflowError, "too many constants");
//         return -1;
//     }
// #endif

//     /* Append folded constant onto consts */
//     if (PyList_Append(consts, newconst)) {
//         Py_DECREF(newconst);
//         return -1;
//     }
//     Py_DECREF(newconst);

//     return copy_op_arg(codestr, c_start, LOAD_CONST,
//                        (unsigned int)index, opcode_end);
// }

// static unsigned int *
// markblocks(_Py_CODEUNIT *code, Py_ssize_t len)
// {
//     unsigned int *blocks = PyMem_New(unsigned int, len);
//     int i, j, opcode, blockcnt = 0;

//     if (blocks == NULL) {
//         PyErr_NoMemory();
//         return NULL;
//     }
//     memset(blocks, 0, len*sizeof(int));

//     /* Mark labels in the first pass */
//     for (i = 0; i < len; i++) {
//         opcode = _Py_OPCODE(code[i]);
//         switch (opcode) {
//             case FOR_ITER:
//             case JUMP_FORWARD:
//             case JUMP_IF_FALSE_OR_POP:
//             case JUMP_IF_TRUE_OR_POP:
//             case POP_JUMP_IF_FALSE:
//             case POP_JUMP_IF_TRUE:
//             case JUMP_IF_NOT_EXC_MATCH:
//             case JUMP_ABSOLUTE:
//             case SETUP_FINALLY:
//             case SETUP_WITH:
//             case SETUP_ASYNC_WITH:
//                 j = GETJUMPTGT(code, i);
//                 assert(j < len);
//                 blocks[j] = 1;
//                 break;
//         }
//     }
//     /* Build block numbers in the second pass */
//     for (i = 0; i < len; i++) {
//         blockcnt += blocks[i];          /* increment blockcnt over labels */
//         blocks[i] = blockcnt;
//     }
//     return blocks;
// }

/* Perform basic peephole optimizations to components of a code object.
   The consts object should still be in list form to allow new constants
   to be appended.

   To keep the optimizer simple, it bails when the lineno table has complex
   encoding for gaps >= 255.

   Optimizations are restricted to simple transformations occurring within a
   single basic block.  All transformations keep the code size the same or
   smaller.  For those that reduce size, the gaps are initially filled with
   NOPs.  Later those NOPs are removed and the jump addresses retargeted in
   a single pass. */

PyObject *
PyCode_Optimize(PyObject *code, PyObject* consts, PyObject *names,
                PyObject *lnotab_obj)
{
    Py_XINCREF(code);
    return code;
}