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bpo-37271: Optimize bytecode multiple times until it cannot be optimized further #14068

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bpo-37271: Optimize bytecode multiple times until it cannot be optimized further #14068

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b90592b
Optimize bytecode multiple times until it cannot be optimized further
pablogsal Jun 14, 2019
c65aa34
Regen importlib
pablogsal Jun 14, 2019
0aa8e9b
Apply suggestions from code review
pablogsal Jul 29, 2019
e148a6f
Add a max iteration cap and adress Zackery feedback
pablogsal Jul 29, 2019
cba4927
Move comment to old function
pablogsal Jul 29, 2019
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pablogsal Sep 9, 2019
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@pablogsal
pablogsal committed Sep 9, 2019
commit 22560ace09692061c12ce08100a42fecbd637317
15 changes: 13 additions & 2 deletions Python/peephole.c
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Original file line number Diff line number Diff line change
Expand Up @@ -21,8 +21,15 @@
(ABSOLUTE_JUMP(_Py_OPCODE(arr[i])) ? 0 : i+1))
#define ISBASICBLOCK(blocks, start, end) \
(blocks[start]==blocks[end])
#define MAX_BYTECODE_OPT_ITERS 5

/* Maximum number of iterations of the main peephole optimizer function
* over the same bytecode object. Theretically, this number can be infinite
* as the peephole optimizer keeps the code object untouched or smaller but
* having a higher bound allows us to scope the performance impact of
* repeating the main peephole optimizer function while making sure than even
* if something goes wrong, the loop will always end. */

#define MAX_BYTECODE_OPT_ITERS 5

/* Scans back N consecutive LOAD_CONST instructions, skipping NOPs,
returns index of the Nth last's LOAD_CONST's EXTENDED_ARG prefix.
Expand Down Expand Up @@ -476,9 +483,13 @@ optimize_bytecode_once(PyObject *code, PyObject* consts, PyObject *names,
cum_orig_offset += lnotab[i];
assert(cum_orig_offset % sizeof(_Py_CODEUNIT) == 0);
index = cum_orig_offset / sizeof(_Py_CODEUNIT);
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if (index >= codelen) {
if (index == codelen) {
/* When running this function multiple times over the same bytecode
* *offset_delta* can be bigger than 255 when the index from the origin
* is exactly as big as the code. In that case we don't need to adjust. */
continue;
} else {
assert(index < codelen);
new_offset = blocks[index] * sizeof(_Py_CODEUNIT);
offset_delta = new_offset - last_offset;
assert(offset_delta < 255);
Expand Down