On Fri, Nov 4, 2016 at 2:15 PM, Richard Biener
<richard.guent...@gmail.com> wrote:
> On Fri, Nov 4, 2016 at 1:34 PM, Marc Glisse <marc.gli...@inria.fr> wrote:
>> Hello,
>>
>> this kind of simplification is already handled by fold_comparison, but the
>> code is common with TRUNC_DIV_EXPR, which yields suboptimal code. In
>> particular, for an unsigned number, X/8==0 means x<=7, while X/[ex]8==0 can
>> be turned into X==0.
>>
>> When we have an explicit division by 0, there is a better optimisation
>> possible (insert __builtin_unreachable() or __builtin_trap() after that
>> statement, as in find_explicit_erroneous_behavior), so I don't touch it.
>>
>> For the overflow inequality case, it would have been a bit clearer to
>> generate
>> (cmp { build_zero_cst (TREE_TYPE (@0)); } @2)
>> and let that be constant folded instead of having that ugly and error-prone
>> test in constant_boolean_node, but I saved one tree ;-)
>>
>> Bootstrap+regtest on powerpc64le-unknown-linux-gnu, all the regressions are
>> in the libitm part of the testsuite, they should be fixed by
>> https://gcc.gnu.org/ml/gcc-patches/2016-10/msg02220.html , I'll rerun the
>> testsuite when that patch is in.
>
> Ok.
>
> You fail to handle A /[ex] -2 < 2? Is that on purpose? Or just lazy so you
> dont' have to handle inverting the comparison?
Oh, I suppose nothing generates exact divisions by negative numbers.
Richard.
> Thanks,
> Richard.
>
>> 2016-11-07 Marc Glisse <marc.gli...@inria.fr>
>>
>> gcc/
>> * fold-const.c (fold_comparison): Ignore EXACT_DIV_EXPR.
>> * match.pd (A /[ex] B CMP C): New simplifications.
>>
>> gcc/testsuite/
>> * gcc.dg/tree-ssa/cmpexactdiv.c: New file.
>>
>> --
>> Marc Glisse
