[Bug target/82830] New: short rotate with truncated length

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82830

            Bug ID: 82830
           Summary: short rotate with truncated length
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: glisse at gcc dot gnu.org
  Target Milestone: ---
            Target: x86_64-*-*

#include <x86intrin.h>
unsigned short f(unsigned short x,int n){
  return _rotwl(x,n&15);
}

        andl    $15, %ecx
        rolw    %cl, %ax

I believe the masking is unnecessary. We have some related things in i386.md,
but only for SWI48.