Delete the redundant conditional statements in traceback.c

[rruuaanng]

Feature or enhancement

cpython/Python/traceback.c

Lines 974 to 985 in 7a2d77c

	dump_frame(fd, frame);
	frame = frame->previous;
	if (frame == NULL) {
	break;
	}
	if (frame->owner == FRAME_OWNED_BY_CSTACK) {
	/* Trampoline frame */
	frame = frame->previous;
	}
	if (frame == NULL) {
	break;
	}

In the above code, it seems that it's redundant.

cpython/Python/traceback.c

Line 983 in 7a2d77c

if (frame == NULL) {

Removing this extra if statement may eliminate the time consumed by the conditional statement.
In

cpython/Python/traceback.c

Lines 975 to 976 in 7a2d77c

	frame = frame->previous;
	if (frame == NULL) {

if frame is empty, it may not be executed

cpython/Python/traceback.c

Lines 979 to 982 in 7a2d77c

	if (frame->owner == FRAME_OWNED_BY_CSTACK) {
	/* Trampoline frame */
	frame = frame->previous;
	}

So it will not be executed

cpython/Python/traceback.c

Lines 983 to 986 in 7a2d77c

	if (frame == NULL) {
	break;
	}
	/* Can't have more than one shim frame in a row */

Logically speaking, if the frame is not NULL, then frame->previous can't be NULL either. This means frame->previous->previous won't be NULL either. If the frame has a forward link, frame->next, then it will have a unique successor.

If there are errors in my proposal or I don't understand the code base, please point out my mistakes, thanks.

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

No response

Linked PRs

• gh-124265: Remove redundant if statements in traceback.c #124272

[skirpichev]

Logically speaking, if the frame is not NULL, then frame->previous can't be NULL either.

Yet, this is tested on L976. Either above statement is false, or L976 test could be removed as well.

[rruuaanng]

Logically speaking, if the frame is not NULL, then frame->previous can't be NULL either.

Yet, this is tested on L976. Either above statement is false, or L976 test could be removed as well.

Maybe I need a minimal test that will trigger the deletion of the if statement.

[skirpichev]

Well, it's clear, that removing this check trigger CI failures. I think it's required.