[Bug rtl-optimization/63259] Detecting byteswap sequence

[thopre01 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63259

--- Comment #12 from thopre01 at gcc dot gnu.org ---
(In reply to Oleg Endo from comment #11)
> (In reply to thopre01 from comment #10)
> > 
> > I have the same gimple and for me the bswap is correctly detected. Can you
> > break at find_bswap_or_nop just after calling find_bswap_or_nop_1 on the if
> > (!source_stmt) and show me the output of p/x n->n ?
> 
> n->n = 0x0000000000000102  limit = 4

That's good, it means the pattern is recognized. Is there an optab defined for
bswap16?

> 
> For both, test_099 and test_08.
> 
> > Indeed, my mistake. Ok I tested a bit and found that the problem is the
> > depth at which it's looking. Try to recompile tree-ssa-math-opts.c after
> > increasing the limit number in find_bswap_or_nop. Right now the limit will
> > evaluate to 4 and the gimple I have has a depth of 5.
> 
> I've tried ...
> 
>   limit += 10 + (int) ceil_log2 ((unsigned HOST_WIDE_INT) limit);
> 
> ... but it doesn't change anything here.

Same as the other pattern, can you try to print n->n in hex with this new
limit? My guess is that the pattern is now recognized but fails later for the
same reason as above.

Best regards.