On Jun 20, 2024, Christophe Lyon <christophe.l...@linaro.org> wrote:
> Maybe using
> if ((unsigned)b[i] >= BITS) \
> would be clearer?
Heh. Why make it simpler if we can make it unreadable, right? :-D
Thanks, here's another version I've just retested on x-arm-eabi. Ok?
I'm not sure how to credit your suggestion. It's not like you pretty
much wrote the entire patch, as in Richard's case, but it's still a
sizable chunk of this two-liner. Any preferences?
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..03078de49c65e 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] >= (unsigned)(BITS)) \
+ __builtin_unreachable(); \
dest[i] = a[i] OP b[i]; \
} \
}
--
Alexandre Oliva, happy hacker https://FSFLA.org/blogs/lxo/
Free Software Activist GNU Toolchain Engineer
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