simplify-rtx: Fix up simplify_logical_relational_operation [PR119002]

The following testcase is miscompiled on powerpc64le-linux starting with
r15-6777.  During combine we see:

(set (reg:SI 134)
    (ior:SI (ge:SI (reg:CCFP 128)
            (const_int 0 [0]))
        (lt:SI (reg:CCFP 128)
            (const_int 0 [0]))))

The simplify_logical_relational_operation code (in its current form)
was written with arithmetic rather than CC modes in mind.  Since CCFP
is a CC mode, it fails the HONOR_NANS check, and so the function assumes
that ge | lt => true.

If one comparison is unsigned then it should be safe to assume that
the other comparison is also unsigned, even for CC modes, since the
optimisation checks that the comparisons are between the same operands.
For the other cases, we can only safely fold comparisons of CC mode
values if the result is always-true (15) or always-false (0).

It turns out that the original testcase for PR117186, which ran at -O,
was relying on the old behaviour for some of the functions.  It needs
4-instruction combinations, and so -fexpensive-optimizations, to pass
in its intended form.

gcc/
	PR rtl-optimization/119002
	* simplify-rtx.cc
	(simplify_context::simplify_logical_relational_operation): Handle
	comparisons between CC values.  If there is no evidence that the
	CC values are unsigned, restrict the fold to always-true or
	always-false results.

gcc/testsuite/
	* gcc.c-torture/execute/ieee/pr119002.c: New test.
	* gcc.target/aarch64/pr117186.c: Run at -O2 rather than -O.

Co-authored-by: Jakub Jelinek <jakub@redhat.com>

0 files changed, 0 insertions, 0 deletions