Normalize jumps in compiler. All forward jumps to use JUMP_FORWARD. (GH-28755)

2 files changed, 35 insertions, 12 deletions

diff --git a/Python/ceval.c b/Python/ceval.c
index 2dbc291897..a3a173dfb7 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -4051,19 +4051,18 @@ check_eval_breaker:
 
         TARGET(JUMP_ABSOLUTE) {
             PREDICTED(JUMP_ABSOLUTE);
-            if (oparg < INSTR_OFFSET()) {
-                /* Increment the warmup counter and quicken if warm enough
-                * _Py_Quicken is idempotent so we don't worry about overflow */
-                if (!PyCodeObject_IsWarmedUp(co)) {
-                    PyCodeObject_IncrementWarmup(co);
-                    if (PyCodeObject_IsWarmedUp(co)) {
-                        if (_Py_Quicken(co)) {
-                            goto error;
-                        }
-                        int nexti = INSTR_OFFSET();
-                        first_instr = co->co_firstinstr;
-                        next_instr = first_instr + nexti;
+            assert(oparg < INSTR_OFFSET());
+            /* Increment the warmup counter and quicken if warm enough
+            * _Py_Quicken is idempotent so we don't worry about overflow */
+            if (!PyCodeObject_IsWarmedUp(co)) {
+                PyCodeObject_IncrementWarmup(co);
+                if (PyCodeObject_IsWarmedUp(co)) {
+                    if (_Py_Quicken(co)) {
+                        goto error;
                     }
+                    int nexti = INSTR_OFFSET();
+                    first_instr = co->co_firstinstr;
+                    next_instr = first_instr + nexti;
                 }
             }
             JUMPTO(oparg);
@@ -4072,6 +4071,7 @@ check_eval_breaker:
         }
 
         TARGET(JUMP_ABSOLUTE_QUICK) {
+            assert(oparg < INSTR_OFFSET());
             JUMPTO(oparg);
             CHECK_EVAL_BREAKER();
             DISPATCH();
diff --git a/Python/compile.c b/Python/compile.c
index 694da29b77..2d82d6a1e5 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -7221,6 +7221,26 @@ 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 &&
+            last->i_target->b_visited == 0
+        ) {
+            last->i_opcode = JUMP_FORWARD;
+        }
+    }
+}
+
+static void
 assemble_jump_offsets(struct assembler *a, struct compiler *c)
 {
     basicblock *b;
@@ -7897,6 +7917,9 @@ assemble(struct compiler *c, int addNone)
         clean_basic_block(b);
     }
 
+    /* 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);