Re: RFC: Patch for switch elimination (PR 54742)

[Richard Biener <richard dot guenther at gmail dot com>]

On August 12, 2014 8:31:16 PM CEST, Jeff Law <law@redhat.com> wrote:
>On 08/12/14 11:46, Steve Ellcey wrote:
>> After talking to Jeff Law at the GCC Cauldron I have updated my
>switch
>> shortcut plugin pass to try and address this optimization in the
>hopes of
>> getting it added to GCC as a static pass.  I fixed the code to build
>with
>> the various C++ changes that have been happening in GCC but the
>current
>> version I have included in this email is not working yet.  When I run
>it
>> on coremark I get errors like:
>>
>> core_state.c: In function 'core_bench_state':
>> core_state.c:43:8: error: size of loop 16 should be 13, not 5
>>   ee_u16 core_bench_state(ee_u32 blksize, ee_u8 *memblock,
>>          ^
>> core_state.c:43:8: error: bb 15 does not belong to loop 16
>> core_state.c:43:8: error: bb 113 does not belong to loop 16
>> core_state.c:43:8: error: bb 118 does not belong to loop 16
>> core_state.c:43:8: error: bb 117 does not belong to loop 16
>> (etc)
>>
>> Apparently there have been some changes to the loop information that
>> is built since GCC 4.9.  I had hoped that adding a call to
>fix_loop_structure
>> after recalculating the dominance information would fix this but it
>didn't.
>>
>> Does anyone have any ideas on how to fix up the loop information that
>my
>> optimization has messed as it duplicates blocks?  I tried adding a
>call
>> 'loop_optimizer_init (LOOPS_NORMAL)' before the fix_loop_structure
>but that
>> did not seem to have any affect.
>Try setting the header & latch fields for the loop structure to NULL, 
>then call loops_set_state (LOOPS_NEED_FIXUP).

But that is _not_ the appropriate way of keeping loops preserved!

Richard.

>Jeff