[3.10] bpo-46724: Use `JUMP_ABSOLUTE` for all backward jumps. (GH-31326) (GH-31354)
diff --git a/Python/compile.c b/Python/compile.c
index a7f62bb..1416eb1 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -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() */
@@ -6702,6 +6704,31 @@ assemble_emit(struct assembler *a, struct instr *i)
}
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)
{
basicblock *b;
@@ -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);