Re: [PATCH for-9.0] tcg/optimize: Fix sign_mask for logical right-shift

[Philippe Mathieu-Daudé]

On 26/3/24 23:22, Richard Henderson wrote:
> The 'sign' computation is attempting to locate the sign bit that has
> been repeated, so that we can test if that bit is known zero.  That
> computation can be zero if there are no known sign repetitions.
>
> Cc: qemu-stable@nongnu.org
> Fixes: 93a967fbb57 ("tcg/optimize: Propagate sign info for shifting")
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2248
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>   tcg/optimize.c                    |  2 +-
>   tests/tcg/aarch64/test-2248.c     | 25 +++++++++++++++++++++++++
>   tests/tcg/aarch64/Makefile.target |  1 +
>   3 files changed, 27 insertions(+), 1 deletion(-)
>   create mode 100644 tests/tcg/aarch64/test-2248.c


> diff --git a/tests/tcg/aarch64/test-2248.c b/tests/tcg/aarch64/test-2248.c
> new file mode 100644
> index 0000000000..6cc20e3c6c
> --- /dev/null
> +++ b/tests/tcg/aarch64/test-2248.c
> @@ -0,0 +1,25 @@

  /* SPDX-License-Identifier: GPL-2.0-or-later */

  /* See https://gitlab.com/qemu-project/qemu/-/issues/2248 */

> +#include <assert.h>
> +
> +__attribute__((noinline))
> +long test(long x, long y, long sh)
> +{
> +    long r;
> +    asm("cmp   %1, %2\n\t"
> +        "cset  x12, lt\n\t"
> +        "and   w11, w12, #0xff\n\t"
> +        "cmp   w11, #0\n\t"
> +        "csetm x14, ne\n\t"
> +        "lsr   x13, x14, %3\n\t"
> +        "sxtb  %0, w13"
> +        : "=r"(r)
> +        : "r"(x), "r"(y), "r"(sh)
> +        : "x11", "x12", "x13", "x14");
> +    return r;
> +}
> +
> +int main()
> +{
> +    long r = test(0, 1, 2);
> +    assert(r == -1);
> +    return 0;
> +}

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>