On Jun 19, 2024, "Richard Earnshaw (lists)" <richard.earns...@arm.com> wrote:
> It looks like adding
> if ((unsigned)b[i] >= 8*sizeof (TYPE##BITS##_t)) \
> __builtin_unreachable(); \
Ah, yes, nice, good idea, thanks!
Here's the patch that implements that, co-attributed to you, as IMHO it
should be; please let me know if you find otherwise. The commit message
is mostly unchanged from v1, except for the very end. Tested on
x86_64-linux-gnu-x-arm-eabi. Ok to install?
The test was too optimistic, alas. We used to vectorize shifts
involving 8-bit and 16-bit integral types by clamping the shift count
at the highest in-range shift count, but that was not correct: such
narrow shifts expect integral promotion, so larger shift counts should
be accepted. (int16_t)32768 >> (int16_t)16 must yield 0, not 1 (as
before the fix).
Unfortunately, in the gimple model of vector units, such large shift
counts wouldn't be well-defined, so we won't vectorize such shifts any
more, unless we can tell they're in range or undefined.
So the test that expected the incorrect clamping we no longer perform
needs to be adjusted. Instead of nobbling the test, Richard Earnshaw
suggested annotating the test with the expected ranges so as to enable
the optimization.
Co-Authored-By: Richard Earnshaw <richard.earns...@arm.com>
for gcc/testsuite/ChangeLog
PR tree-optimization/113281
* gcc.target/arm/simd/mve-vshr.c: Add expected ranges.
---
gcc/testsuite/gcc.target/arm/simd/mve-vshr.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/gcc/testsuite/gcc.target/arm/simd/mve-vshr.c
b/gcc/testsuite/gcc.target/arm/simd/mve-vshr.c
index 8c7adef9ed8f1..35cd0e75be5dc 100644
--- a/gcc/testsuite/gcc.target/arm/simd/mve-vshr.c
+++ b/gcc/testsuite/gcc.target/arm/simd/mve-vshr.c
@@ -9,6 +9,8 @@
void test_ ## NAME ##_ ## SIGN ## BITS ## x ## NB (TYPE##BITS##_t *
__restrict__ dest, TYPE##BITS##_t *a, TYPE##BITS##_t *b) { \
int i; \
for (i=0; i<NB; i++) { \
+ if ((unsigned)b[i] >= __CHAR_BIT__ * sizeof (TYPE##BITS##_t)) \
+ __builtin_unreachable(); \
dest[i] = a[i] OP b[i]; \
} \
}
--
Alexandre Oliva, happy hacker https://FSFLA.org/blogs/lxo/
Free Software Activist GNU Toolchain Engineer
More tolerance and less prejudice are key for inclusion and diversity
Excluding neuro-others for not behaving ""normal"" is *not* inclusive
