328896 - MarkGCThing: stricter tail recursion

Status: RESOLVED FIXED

(Core :: JavaScript Engine, enhancement)

Description

[Igor Bukanov]

Currently MarkGCThing from jsgc.c contains the following code:

start:
...
    if (*flagp & GCF_MARK) {
        /*
         * This should happen only if recursive MARK_GC_THING marks flags
         * already stored in the caller's *next_flagp.
         */
        goto out;
    }


The situation described in the comments happens during marking of object's slots when recursive MARK_GC_THING invocation marks object referenced through next_thing. It is better to move the check there and add assert to require *flagp to be unmarked.

Comment 1

[Igor Bukanov]

Attachment: Implementation and clenups

Besides moving the code to check for a marked thing to where it belongs the patch changes the return type for NarkGCThing to void and makes tail recusrion eleimination slightly more readable. See also bug 324278.

Comment 2

[Brendan Eich [:brendan]]

Comment on attachment 213506 [details] [diff] [review]
Implementation and clenups

Cool -- only thoughts are these very minor comments:

1.  Save one goto by putting onTailRecursion: label and code in place of the patch's second goto onTailRecursion.

2.  SpiderMonkey has an esoteric style rule that prefers out_of_memory for long label names, not camelCaps.  You are now entering the ascended master SpiderMonkey level ;-).

/be

Comment 3

[Igor Bukanov]

Attachment: Nits etc.

Besides addressing the nits the patch removes "out" label replacing all "goto out;" by "break;".

Comment 4

[Brendan Eich [:brendan]]

Comment on attachment 214509 [details] [diff] [review]
Nits etc.

Great!  Thanks,

/be

Comment 5

[Igor Bukanov]

Attachment: Patch to commit with trailing blanks removed

Comment 6

[Igor Bukanov]

I committed the last patch:

Checking in jsgc.c;
/cvsroot/mozilla/js/src/jsgc.c,v  <--  jsgc.c
new revision: 3.119; previous revision: 3.118
done