8000 bpo-42615: Delete redundant jump instructions that only bypass empty blocks by OxyMagnesium · Pull Request #23733 · python/cpython · GitHub
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bpo-42615: Delete redundant jump instructions that only bypass empty blocks #23733

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Merged
merged 8 commits into from
Dec 16, 2020
Merged

bpo-42615: Delete redundant jump instructions that only bypass empty blocks #23733

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ae01647
Delete jump instructions that bypass empty blocks
OxyMagnesium Dec 10, 2020
9740892
Add news entry
OxyMagnesium Dec 10, 2020
6533254
Explicitly check for unconditional jump opcodes
OxyMagnesium Dec 10, 2020
f661a07
Handle conditional jumps, delete jumps gracefully
OxyMagnesium Dec 12, 2020
6b81038
Ensure b_nofallthrough and b_reachable are valid
OxyMagnesium Dec 14, 2020
a6fbdd8
Add test for redundant jumps
OxyMagnesium Dec 14, 2020
2f4e5d3
Regenerate importlib.h and edit Misc/ACKS
OxyMagnesium Dec 16, 2020
51157c1
Fix bad whitespace
OxyMagnesium Dec 16, 2020
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Ensure b_nofallthrough and b_reachable are valid
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@OxyMagnesium
OxyMagnesium committed Dec 16, 2020
commit 6b81038b0e4d9b79beed44887190087964d9e5f2
9 changes: 7 additions & 2 deletions Python/compile.c
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Original file line number Diff line number Diff line change
Expand Up @@ -6437,6 +6437,7 @@ optimize_cfg(struct assembler *a, PyObject *consts)
for (basicblock *b = a->a_entry; b != NULL; b = b->b_next) {
if (b->b_reachable == 0) {
b->b_iused = 0;
b->b_nofallthrough = 0;
}
}
/* Delete jump instructions made redundant by previous step. If a non-empty
Expand All @@ -6453,8 +6454,6 @@ optimize_cfg(struct assembler *a, PyObject *consts)
b_last_instr->i_opcode == JUMP_FORWARD) {
basicblock *b_next_act = b->b_next;
while (b_next_act != NULL && b_next_act->b_iused == 0) {
/* Next line reqd to prevent assertion failure in stackdepth() */
b_next_act->b_nofallthrough = 0;
b_next_act = b_next_act->b_next;
}
if (b_last_instr->i_target == b_next_act) {
Expand All @@ -6472,6 +6471,12 @@ optimize_cfg(struct assembler *a, PyObject *consts)
clean_basic_block(b);
break;
}
/* The blocks after this one are now reachable through it */
b_next_act = b->b_next;
while (b_next_act != NULL && b_next_act->b_iused == 0) {
b_next_act->b_reachable = 1;
b_next_act = b_next_act->b_next;
}
}
}
}
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