On 1/16/21 11:19 AM, Jakub Jelinek via Gcc-patches wrote:
> Hi!
>
> This patch adds some ctz simplifications (e.g. ctz (x) >= 3 can be done by
> testing if the low 3 bits are zero, etc.).
>
> In addition, I've noticed that in the CLZ case, the
> #ifdef CLZ_DEFINED_VALUE_AT_ZERO don't really work as intended, they
> are evaluated during genmatch and the macro is not defined then
> (but, because of the missing tm.h includes it isn't defined in
> gimple-match.c or generic-match.c either). And when tm.h is included,
> defaults.h is included which defines a fallback version of that macro.
>
> For GCC 12, I wonder if it wouldn't be better to say in addition to
> __builtin_c[lt]z*
> is always UB at zero that it would be undefined for .C[LT]Z ifn too if it
> has just one operand and use a second operand to be the constant we expect
> at zero.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> 2021-01-16 Jakub Jelinek <ja...@redhat.com>
>
> PR tree-optimization/95527
> * generic-match-head.c: Include tm.h.
> * gimple-match-head.c: Include tm.h.
> * match.pd (CLZ == INTEGER_CST): Don't use
> #ifdef CLZ_DEFINED_VALUE_AT_ZERO, only test CLZ_DEFINED_VALUE_AT_ZERO
> if clz == CFN_CLZ. Add missing val declaration.
> (CTZ cmp CST): New simplifications.
>
> * gcc.dg/tree-ssa/pr95527-2.c: New test.
Similarly. I'd lean towards deferring to gcc-12.
jeff
