[x86 PATCH] Provide zero_extend versions/variants of several patterns.

[Jeff Law]

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