On 7/31/23 15:43, Prathamesh Kulkarni via Gcc-patches wrote:
On Mon, 19 Jun 2023 at 19:59, Stefan Schulze Frielinghaus via
Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
Comparisons between memory and constants might be done in a smaller mode
resulting in smaller constants which might finally end up as immediates
instead of in the literal pool.
For example, on s390x a non-symmetric comparison like
x <= 0x3fffffffffffffff
results in the constant being spilled to the literal pool and an 8 byte
memory comparison is emitted. Ideally, an equivalent comparison
x0 <= 0x3f
where x0 is the most significant byte of x, is emitted where the
constant is smaller and more likely to materialize as an immediate.
Similarly, comparisons of the form
x >= 0x4000000000000000
can be shortened into x0 >= 0x40.
Bootstrapped and regtested on s390x, x64, aarch64, and powerpc64le.
Note, the new tests show that for the mentioned little-endian targets
the optimization does not materialize since either the costs of the new
instructions are higher or they do not match. Still ok for mainline?
Hi Stefan,
Unfortunately this patch (committed in 7cdd0860949c6c3232e6cff1d7ca37bb5234074c)
caused the following ICE on armv8l-unknown-linux-gnu:
during RTL pass: combine
../../../gcc/libgcc/fixed-bit.c: In function ‘__gnu_saturate1sq’:
../../../gcc/libgcc/fixed-bit.c:210:1: internal compiler error: in
decompose, at rtl.h:2297
210 | }
| ^
0xaa23e3 wi::int_traits<std::pair<rtx_def*, machine_mode>
::decompose(long long*, unsigned int, std::pair<rtx_def*,
machine_mode> const&)
../../gcc/gcc/rtl.h:2297
[ ... ]
Yea, we're seeing something very similar on nios2-linux-gnu building the
kernel.
Prathamesh, can you extract the .i file for fixed-bit on armv8 and open
a bug for this issue, attaching the .i file as well as the right command
line options necessary to reproduce the failure. THat way Stefan can
tackle it with a cross compiler.
Thanks,
jeff
