Move remaining flag_unsafe_math_optimizations using simplify and match
Marc Glisse
marc.glisse@inria.fr
Fri Aug 28 07:15:00 GMT 2015
On Thu, 27 Aug 2015, Andreas Schwab wrote:
> "Hurugalawadi, Naveen" <Naveen.Hurugalawadi@caviumnetworks.com> writes:
>
>> * fold-const.c (fold_binary_loc) : Move Optimize
>> root(x)*root(y) as root(x*y) to match.pd.
>> Move Optimize expN(x)*expN(y) as expN(x+y) to match.pd.
>> Move Optimize pow(x,y)*pow(x,z) as pow(x,y+z) to match.pd.
>> Move Optimize a/root(b/c) into a*root(c/b) to match.pd.
>> Move Optimize x/expN(y) into x*expN(-y) to match.pd.
>>
>> * match.pd (mult (root:s @0) (root:s @1)): New simplifier.
>> (mult (POW:s @0 @1) (POW:s @0 @2)) : New simplifier.
>> (mult (exps:s @0) (exps:s @1)) : New simplifier.
>> (rdiv @0 (root:s (rdiv:s @1 @2))) : New simplifier.
>> (rdiv @0 (exps:s @1)) : New simplifier.
>
> FAIL: gcc.dg/builtins-11.c (test for excess errors)
> Excess errors:
> builtins-11.c:(.text+0x52): undefined reference to `link_error'
Indeed, generic-match ends up testing for sqrt(x)*sqrt(y) before testing
for sqrt(x)@1*@1, so it simplifies it to sqrt(x*x)->abs(x) instead of
plain x. Changing the genmatch machinery to better respect the order of
patterns in match.pd might not be trivial without sacrificing performance,
a workaround might be to add a special pattern sqrt(x)*sqrt(x), or to
disable some patterns for GENERIC so CSE has a chance to run first.
--
Marc Glisse
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