On Thu, 27 Aug 2015, Andreas Schwab wrote:
"Hurugalawadi, Naveen" <naveen.hurugalaw...@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
