[Bug tree-optimization/63464] compare one character to many: faster

[rguenther at suse dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63464

--- Comment #11 from rguenther at suse dot de <rguenther at suse dot de> ---
On Mon, 13 Oct 2014, jakub at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63464
> 
> --- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
> Created attachment 33697
>   --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33697&action=edit
> gcc5-pr63464.patch
> 
> WIP patch.  What is missing:
> 1) the optimize_range_tests_to_bit_test call should be guarded by
> lshift_cheap_p (), Richard, any preference on where to declare that function
> (tree-switch-conversion.h and include that in tree-ssa-reassoc.c, somewhere
> else?)

In optabs.[ch]?

> 2) much more importantly, it right now doesn't actually fixup the IL, so 
> instead of the desirable jump around the shift we have there just 
> BIT_IOR_EXPR (and the shift actually happens to be done first, before 
> the range test). Richard, any preference how to represent it in the IL 
> from in between the optimization and fixup once all bbs are 
> reassociated?  I've been thinking about e.g. some pass-through internal 
> call on the TRUTH_ORIF_EXPR operand.  Another option might be, if we'd 
> adjust update_range_test, so that it would not only emit a 
> gimplification of the range test, but also an optional gimple_seq before 
> that, would be to push all the SSA_NAMEs that would be otherwise passed 
> to the internal call, into some vector, and just split bb after the def 
> stmt of those SSA_NAMEs and also before the (single, hopefully) user of 
> that SSA_NAME, adding an edge around the middle of the bb and PHI.

Can't you "queue" the BIT_IOR_EXPR stmt somewhere and after reassoc
finished split the BBs as desired?

Richard.