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[3.10] bpo-46724: Use JUMP_ABSOLUTE for all backward jumps. (GH-31326) (GH-31354)

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Mark Shannon 2022-02-16 11:26:02 +00:00 • committed by GitHub
parent 3d407b9311
commit d4e4ef107a
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6 changed files with 47 additions and 14 deletions
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31
Python/compile.c
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@ -128,6 +128,8 @@ typedef struct basicblock_ {
unsigned b_nofallthrough : 1;
/* Basic block exits scope (it ends with a return or raise) */
unsigned b_exit : 1;
/* Used by compiler passes to mark whether they have visited a basic block. */
unsigned b_visited : 1;
/* depth of stack upon entry of block, computed by stackdepth() */
int b_startdepth;
/* instruction offset for block, computed by assemble_jump_offsets() */
@ -6701,6 +6703,31 @@ assemble_emit(struct assembler *a, struct instr *i)
return 1;
}
static void
normalize_jumps(struct assembler *a)
{
for (basicblock *b = a->a_entry; b != NULL; b = b->b_next) {
b->b_visited = 0;
}
for (basicblock *b = a->a_entry; b != NULL; b = b->b_next) {
b->b_visited = 1;
if (b->b_iused == 0) {
continue;
}
struct instr *last = &b->b_instr[b->b_iused-1];
if (last->i_opcode == JUMP_ABSOLUTE) {
if (last->i_target->b_visited == 0) {
last->i_opcode = JUMP_FORWARD;
}
}
if (last->i_opcode == JUMP_FORWARD) {
if (last->i_target->b_visited == 1) {
last->i_opcode = JUMP_ABSOLUTE;
}
}
}
}
static void
assemble_jump_offsets(struct assembler *a, struct compiler *c)
{
@ -7137,6 +7164,10 @@ assemble(struct compiler *c, int addNone)
}
propagate_line_numbers(&a);
guarantee_lineno_for_exits(&a, c->u->u_firstlineno);
/* Order of basic blocks must have been determined by now */
normalize_jumps(&a);
/* Can't modify the bytecode after computing jump offsets. */
assemble_jump_offsets(&a, c);