Hi Jakub,
> While we have at the RTL level noce_try_ifelse_collapse combined with
> simplify_cond_clz_ctz, that optimization doesn't always trigger because
> e.g. on powerpc there is an define_insn to compare a reg against zero and
> copy that register to another one and so we end up with a different pseudo
> in the simplify_cond_clz_ctz test and punt.
>
> For targets that define C?Z_DEFINED_VALUE_AT_ZERO to 2 for certain modes,
> we can optimize it already in phiopt though, just need to ensure that
> we transform the __builtin_c?z* calls into .C?Z ifns because my recent
> VRP changes codified that the builtin calls are always undefined at zero,
> while ifns honor C?Z_DEFINED_VALUE_AT_ZERO equal to 2.
> And, in phiopt we already have popcount handling that does pretty much the
> same thing, except for always using a zero value rather than the one set
> by C?Z_DEFINED_VALUE_AT_ZERO.
>
> So, this patch extends that function to handle not just popcount, but also
> clz and ctz.
this broke sparc-sun-solaris2.11 bootstrap
/vol/gcc/src/hg/master/local/gcc/tree-ssa-phiopt.c: In function 'bool
cond_removal_in_popcount_clz_ctz_pattern(basic_block, basic_block, edge, edge,
gimple*, tree, tree)':
/vol/gcc/src/hg/master/local/gcc/tree-ssa-phiopt.c:1858:27: error: variable
'mode' set but not used [-Werror=unused-but-set-variable]
1858 | scalar_int_mode mode = SCALAR_INT_TYPE_MODE (TREE_TYPE (arg));
| ^~~~
and doubtlessly several other targets that use the defaults.h definition of
#define CTZ_DEFINED_VALUE_AT_ZERO(MODE, VALUE) 0
Rainer
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Rainer Orth, Center for Biotechnology, Bielefeld University
