From 27b69e60daa7b191ee6bc76fb6d5fb7d793062ab Mon Sep 17 00:00:00 2001 From: Brandt Bucher Date: Thu, 11 Nov 2021 11:44:34 -0800 Subject: [PATCH] bpo-45773: Stop "optimizing" certain jump patterns (GH-29505) --- Lib/test/test_peepholer.py | 7 ++ .../2021-11-09-13-01-35.bpo-45773.POU8A4.rst | 1 + Python/compile.c | 117 ++++++------------ 3 files changed, 49 insertions(+), 76 deletions(-) create mode 100644 Misc/NEWS.d/next/Core and Builtins/2021-11-09-13-01-35.bpo-45773.POU8A4.rst diff --git a/Lib/test/test_peepholer.py b/Lib/test/test_peepholer.py index 7086a42b095600..8306c896a57f4e 100644 --- a/Lib/test/test_peepholer.py +++ b/Lib/test/test_peepholer.py @@ -600,5 +600,12 @@ def test_bpo_42057(self): except Exception or Exception: pass + def test_bpo_45773_pop_jump_if_true(self): + compile("while True or spam: pass", "", "exec") + + def test_bpo_45773_pop_jump_if_false(self): + compile("while True or not spam: pass", "", "exec") + + if __name__ == "__main__": unittest.main() diff --git a/Misc/NEWS.d/next/Core and Builtins/2021-11-09-13-01-35.bpo-45773.POU8A4.rst b/Misc/NEWS.d/next/Core and Builtins/2021-11-09-13-01-35.bpo-45773.POU8A4.rst new file mode 100644 index 00000000000000..2b9ba81be233f7 --- /dev/null +++ b/Misc/NEWS.d/next/Core and Builtins/2021-11-09-13-01-35.bpo-45773.POU8A4.rst @@ -0,0 +1 @@ +Fix a compiler hang when attempting to optimize certain jump patterns. diff --git a/Python/compile.c b/Python/compile.c index 8135f187559805..1ae4b6575a7f4c 100644 --- a/Python/compile.c +++ b/Python/compile.c @@ -8052,29 +8052,24 @@ fold_rotations(struct instr *inst, int n) } } - -static int -eliminate_jump_to_jump(basicblock *bb, int opcode) { - assert (bb->b_iused > 0); - struct instr *inst = &bb->b_instr[bb->b_iused-1]; - assert (is_jump(inst)); - assert (inst->i_target->b_iused > 0); - struct instr *target = &inst->i_target->b_instr[0]; - if (inst->i_target == target->i_target) { - /* Nothing to do */ - return 0; - } - int lineno = target->i_lineno; - int end_lineno = target->i_end_lineno; - int col_offset = target->i_col_offset; - int end_col_offset = target->i_end_col_offset; - if (add_jump_to_block(bb, opcode, lineno, end_lineno, col_offset, - end_col_offset, target->i_target) == 0) { - return -1; +// Attempt to eliminate jumps to jumps by updating inst to jump to +// target->i_target using the provided opcode. Return whether or not the +// optimization was successful. +static bool +jump_thread(struct instr *inst, struct instr *target, int opcode) +{ + assert(is_jump(inst)); + assert(is_jump(target)); + // bpo-45773: If inst->i_target == target->i_target, then nothing actually + // changes (and we fall into an infinite loop): + if (inst->i_lineno == target->i_lineno && + inst->i_target != target->i_target) + { + inst->i_target = target->i_target; + inst->i_opcode = opcode; + return true; } - assert (bb->b_iused >= 2); - bb->b_instr[bb->b_iused-2].i_opcode = NOP; - return 0; + return false; } /* Maximum size of basic block that should be copied in optimizer */ @@ -8199,25 +8194,21 @@ optimize_basic_block(struct compiler *c, basicblock *bb, PyObject *consts) where y+1 is the instruction following the second test. */ case JUMP_IF_FALSE_OR_POP: - switch(target->i_opcode) { + switch (target->i_opcode) { case POP_JUMP_IF_FALSE: - if (inst->i_lineno == target->i_lineno) { - *inst = *target; - i--; - } + i -= jump_thread(inst, target, POP_JUMP_IF_FALSE); break; case JUMP_ABSOLUTE: case JUMP_FORWARD: case JUMP_IF_FALSE_OR_POP: - if (inst->i_lineno == target->i_lineno && - inst->i_target != target->i_target) { - inst->i_target = target->i_target; - i--; - } + i -= jump_thread(inst, target, JUMP_IF_FALSE_OR_POP); break; case JUMP_IF_TRUE_OR_POP: - assert (inst->i_target->b_iused == 1); + case POP_JUMP_IF_TRUE: if (inst->i_lineno == target->i_lineno) { + // We don't need to bother checking for loops here, + // since a block's b_next cannot point to itself: + assert(inst->i_target != inst->i_target->b_next); inst->i_opcode = POP_JUMP_IF_FALSE; inst->i_target = inst->i_target->b_next; --i; @@ -8225,27 +8216,22 @@ optimize_basic_block(struct compiler *c, basicblock *bb, PyObject *consts) break; } break; - case JUMP_IF_TRUE_OR_POP: - switch(target->i_opcode) { + switch (target->i_opcode) { case POP_JUMP_IF_TRUE: - if (inst->i_lineno == target->i_lineno) { - *inst = *target; - i--; - } + i -= jump_thread(inst, target, POP_JUMP_IF_TRUE); break; case JUMP_ABSOLUTE: case JUMP_FORWARD: case JUMP_IF_TRUE_OR_POP: - if (inst->i_lineno == target->i_lineno && - inst->i_target != target->i_target) { - inst->i_target = target->i_target; - i--; - } + i -= jump_thread(inst, target, JUMP_IF_TRUE_OR_POP); break; case JUMP_IF_FALSE_OR_POP: - assert (inst->i_target->b_iused == 1); + case POP_JUMP_IF_FALSE: if (inst->i_lineno == target->i_lineno) { + // We don't need to bother checking for loops here, + // since a block's b_next cannot point to itself: + assert(inst->i_target != inst->i_target->b_next); inst->i_opcode = POP_JUMP_IF_TRUE; inst->i_target = inst->i_target->b_next; --i; @@ -8253,54 +8239,33 @@ optimize_basic_block(struct compiler *c, basicblock *bb, PyObject *consts) break; } break; - case POP_JUMP_IF_FALSE: - switch(target->i_opcode) { + switch (target->i_opcode) { case JUMP_ABSOLUTE: case JUMP_FORWARD: - if (inst->i_lineno == target->i_lineno) { - inst->i_target = target->i_target; - i--; - } - break; + case JUMP_IF_FALSE_OR_POP: + i -= jump_thread(inst, target, POP_JUMP_IF_FALSE); } break; - case POP_JUMP_IF_TRUE: - switch(target->i_opcode) { + switch (target->i_opcode) { case JUMP_ABSOLUTE: case JUMP_FORWARD: - if (inst->i_lineno == target->i_lineno) { - inst->i_target = target->i_target; - i--; - } - break; + case JUMP_IF_TRUE_OR_POP: + i -= jump_thread(inst, target, POP_JUMP_IF_TRUE); } break; - case JUMP_ABSOLUTE: case JUMP_FORWARD: - assert (i == bb->b_iused-1); - switch(target->i_opcode) { - case JUMP_FORWARD: - if (eliminate_jump_to_jump(bb, inst->i_opcode)) { - goto error; - } - break; - + switch (target->i_opcode) { case JUMP_ABSOLUTE: - if (eliminate_jump_to_jump(bb, JUMP_ABSOLUTE)) { - goto error; - } - break; + case JUMP_FORWARD: + i -= jump_thread(inst, target, JUMP_ABSOLUTE); } break; case FOR_ITER: - assert (i == bb->b_iused-1); if (target->i_opcode == JUMP_FORWARD) { - if (eliminate_jump_to_jump(bb, inst->i_opcode)) { - goto error; - } + i -= jump_thread(inst, target, FOR_ITER); } break; case ROT_N: