https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96373
--- Comment #14 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The trunk branch has been updated by Richard Sandiford <rsand...@gcc.gnu.org>: https://gcc.gnu.org/g:7486fe153adaa868f36248b72f3e78d18b1b3ba1 commit r13-5458-g7486fe153adaa868f36248b72f3e78d18b1b3ba1 Author: Richard Sandiford <richard.sandif...@arm.com> Date: Fri Jan 27 17:03:51 2023 +0000 Add support for conditional xorsign [PR96373] This patch is an optimisation, but it's also a prerequisite for fixing PR96373 without regressing vect-xorsign_exec.c. Currently the vectoriser vectorises: for (i = 0; i < N; i++) r[i] = a[i] * __builtin_copysignf (1.0f, b[i]); as two unconditional operations (copysign and mult). tree-ssa-math-opts.cc later combines them into an "xorsign" function. This works for both Advanced SIMD and SVE. However, with the fix for PR96373, the vectoriser will instead generate a conditional multiplication (IFN_COND_MUL). Something then needs to fold copysign & IFN_COND_MUL to the equivalent of a conditional xorsign. Three obvious options were: (1) Extend tree-ssa-math-opts.cc. (2) Do the fold in match.pd. (3) Leave it to rtl combine. I'm against (3), because this isn't a target-specific optimisation. (1) would be possible, but would involve open-coding a lot of what match.pd does for us. And, in contrast to doing the current tree-ssa-math-opts.cc optimisation in match.pd, there should be no danger of (2) happening too early. If we have an IFN_COND_MUL then we're already past the stage of simplifying the original source code. There was also a choice between adding a conditional xorsign ifn and simply open-coding the xorsign. The latter seems simpler, and means less boiler-plate for target-specific code. The signed_or_unsigned_type_for change is needed to make sure that we stay in "SVE space" when doing the optimisation on 128-bit fixed-length SVE. gcc/ PR tree-optimization/96373 * tree.h (sign_mask_for): Declare. * tree.cc (sign_mask_for): New function. (signed_or_unsigned_type_for): For vector types, try to use the related_int_vector_mode. * genmatch.cc (commutative_op): Handle conditional internal functions. * match.pd: Fold an IFN_COND_MUL+copysign into an IFN_COND_XOR+and. gcc/testsuite/ PR tree-optimization/96373 * gcc.target/aarch64/sve/cond_xorsign_1.c: New test. * gcc.target/aarch64/sve/cond_xorsign_2.c: Likewise.
