On Thu, Oct 12, 2017 at 8:32 AM, Uros Bizjak <ubiz...@gmail.com> wrote: > On Wed, Oct 11, 2017 at 10:59 PM, Jakub Jelinek <ja...@redhat.com> wrote: >> Hi! >> >> As can be seen on the testcase below, the *<rotate_insn><mode>3_mask >> insn/splitter is able to optimize only the case when the and is >> performed in SImode and then the result subreged into QImode, >> while if the computation is already in QImode, we don't handle it. >> >> Fixed by adding another pattern, bootstrapped/regtested on x86_64-linux and >> i686-linux, ok for trunk? > > We probably want to add this variant to *all* *_mask splitters (there > are a few of them in i386.md, please grep for "Avoid useless > masking"). Which finally begs a question - should we implement this > simplification in a generic, target-independent way? OTOH, we already > have SHIFT_COUNT_TRUNCATED and shift_truncation_mask hooks, but last > time I try the former, there were some problems in the testsuite on > x86. I guess there are several targets that would benefit from > removing useless masking of count operands.
Oh, and there is a strange x86 exception in the comment for SHIFT_COUNT_TRUNCATED. I'm not sure what "(real or pretended) bit-field operation" means, but variable-count BT instruction with non-memory operand (we never generate variable-count BTx with memory operand) masks its count operand as well. Uros.
