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bpo-42908: Eliminate NOPs in extended blocks. #24209

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Jan 13, 2021
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bpo-42908: Eliminate NOPs in extended blocks. #24209

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18 changes: 13 additions & 5 deletions Python/compile.c
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Original file line number Diff line number Diff line change
Expand Up @@ -6328,10 +6328,9 @@ optimize_basic_block(basicblock *bb, PyObject *consts)


static void
clean_basic_block(basicblock *bb) {
/* Remove NOPs. */
clean_basic_block(basicblock *bb, int prev_lineno) {
/* Remove NOPs when legal to do so. */
int dest = 0;
int prev_lineno = -1;
for (int src = 0; src < bb->b_iused; src++) {
int lineno = bb->b_instr[src].i_lineno;
if (bb->b_instr[src].i_opcode == NOP) {
Expand Down Expand Up @@ -6531,7 +6530,7 @@ optimize_cfg(struct assembler *a, PyObject *consts)
if (optimize_basic_block(b, consts)) {
return -1;
}
clean_basic_block(b);
clean_basic_block(b, -1);
assert(b->b_predecessors == 0);
}
if (mark_reachable(a)) {
Expand All @@ -6544,6 +6543,15 @@ optimize_cfg(struct assembler *a, PyObject *consts)
b->b_nofallthrough = 0;
}
}
basicblock *pred = NULL;
for (basicblock *b = a->a_entry; b != NULL; b = b->b_next) {
int prev_lineno = -1;
if (pred && pred->b_iused) {
prev_lineno = pred->b_instr[pred->b_iused-1].i_lineno;
}
clean_basic_block(b, prev_lineno);
pred = b->b_nofallthrough ? NULL : b;
}
eliminate_empty_basic_blocks(a->a_entry);
/* Delete jump instructions made redundant by previous step. If a non-empty
block ends with a jump instruction, check if the next non-empty block
Expand Down Expand Up @@ -6571,7 +6579,7 @@ optimize_cfg(struct assembler *a, PyObject *consts)
case JUMP_ABSOLUTE:
case JUMP_FORWARD:
b_last_instr->i_opcode = NOP;
clean_basic_block(b);
clean_basic_block(b, -1);
maybe_empty_blocks = 1;
break;
}
Expand Down