> > On Oct 1, 2015, at 6:57 AM, James Greenhalgh <james.greenha...@arm.com> wrote: > > > Hi, > > If it is cheap enough to treat a floating-point value as an integer and > to do bitwise arithmetic on it (as it is for AArch64) we can rewrite: > > x * copysign (1.0, y) > > as: > > x ^ (y & (1 << sign_bit_position))
Why not just convert it to copysign (x, y) instead and let expand chose the better implementation? Also I think this can only be done for finite and non trapping types. Thanks, Andrew > > This patch implements that rewriting rule in match.pd, and a testcase > expecting the transform. > > This is worth about 6% in 481.wrf for AArch64. I don't don't know enough > about the x86 microarchitectures to know how productive this transformation > is there. In Spec2006FP I didn't see any interesting results in either > direction. Looking at code generation for the testcase I add, I think the > x86 code generation looks worse, but I can't understand why it doesn't use > a vector-side xor and load the mask vector-side. With that fixed up I think > the code generation would look better - though as I say, I'm not an expert > here... > > Bootstrapped on both aarch64-none-linux-gnu and x86_64 with no issues. > > OK for trunk? > > Thanks, > James > > --- > gcc/ > > 2015-10-01 James Greenhalgh <james.greenha...@arm.com> > > * match.pd (mult (COPYSIGN:s real_onep @0) @1): New simplifier. > > gcc/testsuite/ > > 2015-10-01 James Greenhalgh <james.greenha...@arm.com> > > * gcc.dg/tree-ssa/copysign.c: New. > > <0001-Patch-match.pd-Add-a-simplify-rule-for-x-copysign-1..patch>
