On 10/10/23 08:41, Michael Matz wrote:
On Tue, 10 Oct 2023, Roger Sayle wrote:
This patch is the middle-end piece of an improvement to PRs 101955 and
106245, that adds a missing simplification to the RTL optimizers.
This transformation is to simplify (char)(x << 7) != 0 as x & 1.
Random observation:
So, why restrict to shifts of LEN-1 and mask 1? It's always the case that
(type-of-LEN)(x << S)) != 0 === (x & ((1 << (LEN - S)) - 1)) != 0.
E.g. (char)(x << 5) != 0 === (x & 7) != 0.
Yea, it probably could be extended as a followup.
(Eventually the mask will be a constant that's too costly to compute if S
is target-dependendly too small, but all else being equal avoiding shifts
seems sensible)
Agreed, though it's nowhere near as important as it was 20+ years ago ;-)
jeff
