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Teach the peepholer to fold unary operations on constants.

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Afterwards, -0.5 loads in a single step and no longer requires a runtime
UNARY_NEGATIVE operation.
This commit is contained in:
Raymond Hettinger 2005-02-20 12:41:32 +00:00
parent 57e7447c44
commit 80121491e0
1 changed files with 62 additions and 0 deletions
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62
Python/compile.c
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@ -542,6 +542,54 @@ fold_binops_on_constants(unsigned char *codestr, PyObject *consts)
return 1;
}
static int
fold_unaryops_on_constants(unsigned char *codestr, PyObject *consts)
{
PyObject *newconst, *v;
int len_consts, opcode;
/* Pre-conditions */
assert(PyList_CheckExact(consts));
assert(codestr[0] == LOAD_CONST);
/* Create new constant */
v = PyList_GET_ITEM(consts, GETARG(codestr, 0));
opcode = codestr[3];
switch (opcode) {
case UNARY_NEGATIVE:
newconst = PyNumber_Negative(v);
break;
case UNARY_CONVERT:
newconst = PyObject_Repr(v);
break;
case UNARY_INVERT:
newconst = PyNumber_Invert(v);
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 LOAD_CONST newconst */
codestr[0] = NOP;
codestr[1] = LOAD_CONST;
SETARG(codestr, 1, len_consts);
return 1;
}
static unsigned int *
markblocks(unsigned char *code, int len)
{
@ -771,6 +819,20 @@ optimize_code(PyObject *code, PyObject* consts, PyObject *names, PyObject *linen
}
break;
/* Fold unary ops on constants.
LOAD_CONST c1 UNARY_OP --> LOAD_CONST unary_op(c) */
case UNARY_NEGATIVE:
case UNARY_CONVERT:
case UNARY_INVERT:
if (lastlc >= 1 &&
ISBASICBLOCK(blocks, i-3, 4) &&
fold_unaryops_on_constants(&codestr[i-3], 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.