Hi all,

In this PR we ICE during combine when trying to propagate a comparison into a vec_duplicate,
that is we end up creating the rtx:
(vec_duplicate:V4SI (eq:CC_NZ (reg:CC_NZ 66 cc)
         (const_int 0 [0])))

The documentation for vec_duplicate says:
"The output vector mode must have the same submodes as the input vector mode or the scalar modes"
So this is invalid RTL, which triggers an assert in simplify-rtx to that effect.

It has been suggested on the PR that this is because we use a special_predicate for
aarch64_comparison_operator which means that it ignores the mode when matching.
This is fine when used in RTXes that don't need it, like if_then_else expressions
but can cause trouble when used in places where the modes do matter, like in
SET operations. In this particular ICE the cause was the conditional store
patterns that could end up matching an intermediate rtx during combine of
(set (reg:SI) (eq:CC_NZ x y)).

The suggested solution is to define a separate predicate with the same
conditions as aarch64_comparison_operator but make it not special, so it gets
automatic mode checks to prevent such a situation.

This patch does that.
Bootstrapped and tested on aarch64-linux-gnu.
SPEC2006 codegen did not change with this patch, so there shouldn't be
any code quality regressions.

Ok for trunk?

Thanks,
Kyrill

2016-01-29  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>

     PR target/69161
     * config/aarch64/predicates.md (aarch64_comparison_operator_mode):
     New predicate.
     (aarch64_comparison_operator): Break overly long line into two.
     (aarch64_comparison_operation): Likewise.
     * config/aarch64/aarch64.md (cstorecc4): Use
     aarch64_comparison_operator_mode instead of
     aarch64_comparison_operator.
     (cstore<mode>4): Likewise.
     (aarch64_cstore<mode>): Likewise.
     (*cstoresi_insn_uxtw): Likewise.
     (cstore<mode>_neg): Likewise.
     (*cstoresi_neg_uxtw): Likewise.

2016-01-29  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>

     PR target/69161
     * gcc.c-torture/compile/pr69161.c: New test.