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Teach the peephole optimizer to fold simple constant expressions.

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Raymond Hettinger 2005-01-02 06:17:33 +00:00
parent 64585988af
commit c34f8673a1
3 changed files with 149 additions and 1 deletions
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119
Python/compile.c
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@ -439,6 +439,99 @@ tuple_of_constants(unsigned char *codestr, int n, PyObject *consts)
return 1;
}
/* Replace LOAD_CONST c1. LOAD_CONST c2 BINOP
with LOAD_CONST binop(c1,c2)
The consts table must still be in list form so that the
new constant can be appended.
Called with codestr pointing to the first LOAD_CONST.
Abandons the transformation if the folding fails (i.e. 1+'a'). */
static int
fold_binops_on_constants(unsigned char *codestr, PyObject *consts)
{
PyObject *newconst, *v, *w;
int len_consts, opcode;
/* Pre-conditions */
assert(PyList_CheckExact(consts));
assert(codestr[0] == LOAD_CONST);
assert(codestr[3] == LOAD_CONST);
/* Create new constant */
v = PyList_GET_ITEM(consts, GETARG(codestr, 0));
w = PyList_GET_ITEM(consts, GETARG(codestr, 3));
opcode = codestr[6];
switch (opcode) {
case BINARY_POWER:
newconst = PyNumber_Power(v, w, Py_None);
break;
case BINARY_MULTIPLY:
newconst = PyNumber_Multiply(v, w);
break;
case BINARY_DIVIDE:
if (!_Py_QnewFlag) {
newconst = PyNumber_Divide(v, w);
break;
}
/* -Qnew is in effect: fall through to
BINARY_TRUE_DIVIDE */
case BINARY_TRUE_DIVIDE:
newconst = PyNumber_TrueDivide(v, w);
break;
case BINARY_FLOOR_DIVIDE:
newconst = PyNumber_FloorDivide(v, w);
break;
case BINARY_MODULO:
newconst = PyNumber_Remainder(v, w);
break;
case BINARY_ADD:
newconst = PyNumber_Add(v, w);
break;
case BINARY_SUBTRACT:
newconst = PyNumber_Subtract(v, w);
break;
case BINARY_SUBSCR:
newconst = PyObject_GetItem(v, w);
break;
case BINARY_LSHIFT:
newconst = PyNumber_Lshift(v, w);
break;
case BINARY_RSHIFT:
newconst = PyNumber_Rshift(v, w);
break;
case BINARY_AND:
newconst = PyNumber_And(v, w);
break;
case BINARY_XOR:
newconst = PyNumber_Xor(v, w);
break;
case BINARY_OR:
newconst = PyNumber_Or(v, w);
break;
default:
/* Called with an unknown opcode */
assert(0);
return 0;
}
if (newconst == NULL) {
PyErr_Clear();
return 0;
}
/* Append folded constant into consts table */
len_consts = PyList_GET_SIZE(consts);
if (PyList_Append(consts, newconst)) {
Py_DECREF(newconst);
return 0;
}
Py_DECREF(newconst);
/* Write NOP NOP NOP NOP LOAD_CONST newconst */
memset(codestr, NOP, 4);
codestr[4] = LOAD_CONST;
SETARG(codestr, 4, len_consts);
return 1;
}
static unsigned int *
markblocks(unsigned char *code, int len)
{
@ -614,7 +707,6 @@ optimize_code(PyObject *code, PyObject* consts, PyObject *names, PyObject *linen
h = i - 3 * j;
if (h >= 0 &&
j <= lastlc &&
codestr[h] == LOAD_CONST &&
ISBASICBLOCK(blocks, h, 3*(j+1)) &&
tuple_of_constants(&codestr[h], j, consts)) {
assert(codestr[i] == LOAD_CONST);
@ -640,6 +732,31 @@ optimize_code(PyObject *code, PyObject* consts, PyObject *names, PyObject *linen
}
break;
/* Fold binary ops on constants.
LOAD_CONST c1 LOAD_CONST c2 BINOP --> LOAD_CONST binop(c1,c2) */
case BINARY_POWER:
case BINARY_MULTIPLY:
case BINARY_DIVIDE:
case BINARY_TRUE_DIVIDE:
case BINARY_FLOOR_DIVIDE:
case BINARY_MODULO:
case BINARY_ADD:
case BINARY_SUBTRACT:
case BINARY_SUBSCR:
case BINARY_LSHIFT:
case BINARY_RSHIFT:
case BINARY_AND:
case BINARY_XOR:
case BINARY_OR:
if (lastlc >= 2 &&
ISBASICBLOCK(blocks, i-6, 7) &&
fold_binops_on_constants(&codestr[i-6], consts)) {
i -= 2;
assert(codestr[i] == LOAD_CONST);
cumlc = 1;
}
break;
/* Simplify conditional jump to conditional jump where the
result of the first test implies the success of a similar
test or the failure of the opposite test.