On 12/27/22 18:15, Roger Sayle wrote:
Back in September, the review of my patch for PR rtl-optimization/106594,
https://gcc.gnu.org/pipermail/gcc-patches/2022-September/601501.html
suggested that I submit the x86 backend bits, independently and first.
The executive summary is that the middle-end doesn't have a preferred
canonical form for expressing zero-extension, sometimes using an AND
and sometimes using zero_extend. Pending changes to RTL simplification
will/may alter some of these representations, so a few additional
patterns are required to recognize these alternate representations
and avoid any testsuite regressions.
Oh and internally other forms can show up. Like paired shifts. In
fact, I think paired shifts are canonical inside at least some parts of
combine.
jeff
