Jakub Jelinek <ja...@redhat.com> writes: > On Wed, Nov 22, 2017 at 10:09:08AM +0000, Richard Sandiford wrote: >> This patch replaces the REDUC_*_EXPR tree codes with internal functions. >> This is needed so that the support for in-order reductions can also use >> internal functions without too much complication. >> >> This came out of the review for: >> https://gcc.gnu.org/ml/gcc-patches/2017-11/msg01516.html >> >> Tested on aarch64-linux-gnu, x86_64-linux-gnu and powerpc64le-linux-gnu. >> OK to install? > > Wouldn't it be better to just have IFN_REDUC that takes as an additional > argument INTEGER_CST with tree_code of the operation (so REDUC_MAX_EXPR > would be transformed into REDUC (MAX_EXPR, ...) etc.)? > That way we wouldn't need to add further internal fns if we want say > multiplication reduction, or some other.
I think it depends how we use them. The functions added here map directly to optabs, so we'd only add a new one if we also added a new optab. If there's no optab, or if there is an optab but the target doesn't support it, then we open-code the reduction during vectorisation. (That open-coding already happens for MULT, AND, IOR and XOR, which have no optabs, although one of the SVE patches does add optabs for the last three.) I think having separate functions makes sense in that case, since it makes the mapping to optabs easier, and makes it easier to probe for target support. Maybe an IFN_REDUC would be useful if we wanted to defer the open-coding of other reductions past vectorisation, but I'm not sure off-hand how useful that would be. E.g. we'd still need to try to cost the eventual expansion when deciding profitability. Thanks, Richard
