On 6/30/2026 8:07 PM, Odysseas Georgoudis wrote:
This patch teaches match.pd to recognize the branchless conditional
negate idiom
(x ^ -cmp) + cmp
when cmp is known to be zero or one. The expression is folded to a
conditional negate form. For the sign-test spelling based on x < 0,
the patch exposes ABS_EXPR.
I could not comment on the PR because my GCC Bugzilla account is still
pending, so I am sending the patch here.
Bootstrapped on x86_64-pc-linux-gnu. Tested with
gcc.dg/tree-ssa/tree-ssa.exp and the new gcc.dg/tree-ssa/pr113894.c
testcase.
I do not have commit access.
pr113894.patch
<https://1drv.ms/u/c/5a41b3fa58bb8071/IQAXsKqhUTaaQb_gOXEu4L8RAXgQUmxYo5d_eBzRtnqcKSI>
Can you include the patch in your message. It looks like the link goes
to onedrive and I suspect many folks aren't going to want to do that.
Interestingly enough the (x ^ -cmp) + cmp form is probably optimal on
RISC-V, so hopefully even after your match.pd change we'll still be able
to recover optimal form across different designs.
jeff
