On February 4, 2015 10:20:06 PM CET, Sebastian Pop <seb...@gmail.com> wrote:
>Hi,
>
>The attached patch stops the recursion in the detection of FSM
>jump-threads at
>loop phi nodes after having visited a loop phi node. This avoids
>jump-threading
>two iterations forward that were possible due to a flip-flop operation
>that
>exchange the value of the switch control variable as illustrated in the
>testcase:
>
>do {
> c = read_from_memory;
> switch (a) {
> case 0:
> if (c == ' ')
> [...]
> else
> a = b; // flip-flop
> break;
> case 1:
> a = 0;
> b = 15; // this will jump-thread to 15
> break;
>
> case 15:
> [...]
> }
>} while (...);
>
>The patch has passed bootstrap and regression testing on x86_64-linux.
>Ok to commit?
But is sounds like a useful optimization?
Richard.
>Thanks,
>Sebastian
