Greg McGary <g...@rivosinc.com> 于2024年1月17日周三 06:20写道：
>
> The sign bit of a sign-extending load cannot be known until runtime,
> so don't attempt to simplify it in the combiner.
>
> 2024-01-11 Greg McGary <g...@rivosinc.com>
>
> PR rtl-optimization/113010
> * combine.cc (expand_compound_operation): Don't simplify
> SIGN_EXTEND of a MEM on WORD_REGISTER_OPERATIONS targets
>
> * gcc.c-torture/execute/pr113010.c: New test.
> ---
> gcc/combine.cc | 5 +++++
> gcc/testsuite/gcc.c-torture/execute/pr113010.c | 9 +++++++++
> 2 files changed, 14 insertions(+)
> create mode 100644 gcc/testsuite/gcc.c-torture/execute/pr113010.c
>
> diff --git a/gcc/combine.cc b/gcc/combine.cc
> index 812553c091e..ba587184dfc 100644
> --- a/gcc/combine.cc
> +++ b/gcc/combine.cc
> @@ -7208,6 +7208,11 @@ expand_compound_operation (rtx x)
> if (len == 0)
> return x;
>
> + /* Sign-extending loads can never be simplified at compile time. */
> + if (WORD_REGISTER_OPERATIONS && MEM_P (XEXP (x, 0))
> + && load_extend_op (inner_mode) == SIGN_EXTEND)
> + return x;
> +
> break;
>
> case ZERO_EXTRACT:
> diff --git a/gcc/testsuite/gcc.c-torture/execute/pr113010.c
> b/gcc/testsuite/gcc.c-torture/execute/pr113010.c
> new file mode 100644
> index 00000000000..a95c613c1df
> --- /dev/null
> +++ b/gcc/testsuite/gcc.c-torture/execute/pr113010.c
> @@ -0,0 +1,9 @@
> +int minus_1 = -1;
> +
> +int
> +main ()
> +{
> + if ((0, 0xfffffffful) >= minus_1)
There is a warning option:
-Wsign-compare
Warn when a comparison between signed and unsigned values could
produce an incorrect result when the signed value is converted to unsigned.
> + __builtin_abort ();
> + return 0;
> +}
> --
> 2.34.1
>
--
YunQiang Su
