Folks,
we'd appreciate it if someone could take the time to review this fix
for PR116845.
Thanks,
Philipp.
On Tue, 31 Dec 2024 at 10:03, Konstantinos Eleftheriou
<konstantinos.elefther...@vrull.eu> wrote:
>
> From: kelefth <konstantinos.elefther...@vrull.eu>
>
> `(A * B) + (-C) to (B - C/A) * A` fails to match on ILP32 targets due to
> the upper bits of CST0 being zeros in some cases.
>
> This patch adds the following pattern in match.pd:
> (A + CST0) * CST1 -> (A + CST0') * CST1, where CST1 is a power of 2
> constant and CST0' is CST0 with the log2(CST1) MS bits sign-extended.
>
> This pattern sign-extends the log2(CST1) MS bits of CST0, in case that
> the bit that follows them is set. These bits will be pushed out by
> the multiplication with CST1.
>
> Bootstrapped/regtested on x86 and AArch64.
>
> PR tree-optimization/116845
>
> gcc/ChangeLog:
>
> * match.pd: New pattern.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.target/i386/pr116845.c: New test.
> ---
> gcc/match.pd | 21 ++++++++++++++++++++-
> gcc/testsuite/gcc.target/i386/pr116845.c | 23 +++++++++++++++++++++++
> 2 files changed, 43 insertions(+), 1 deletion(-)
> create mode 100644 gcc/testsuite/gcc.target/i386/pr116845.c
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index 83eca8b2e0a..aa2108726f9 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -4400,7 +4400,26 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> /* Calculate @2 / @0 in order to factorize the expression. */
> wide_int div_res = wi::sdiv_trunc (c2, c0);
> tree div_cst = wide_int_to_tree (type, div_res); }
> - (mult (plus @1 { div_cst; }) @0))))))))
> + (mult (plus @1 { div_cst; }) @0)))))))
> + /* (A + CST0) * CST1 -> (A + CST0') * CST1, where CST1 is a power of 2
> + constant and CST0' is CST0 with the log2(CST1) MS bits sign-extended. */
> + (simplify
> + (mult (plus:c @0 INTEGER_CST@1) integer_pow2p@2)
> + (with { wide_int c1 = wi::to_wide (@1); }
> + (if (!wi::neg_p (c1))
> + (with {
> + int bits_to_extend = wi::exact_log2 (wi::to_wide (@2));
> + uint rest_bits = tree_to_uhwi (TYPE_SIZE (type)) - bits_to_extend;
> + /* Get the value of the MSB of the rest_bits. */
> + wide_int bitmask = wi::set_bit_in_zero (rest_bits - 1,
> + TYPE_PRECISION (type));
> + wide_int bit_value = wi::lrshift (c1 & bitmask, rest_bits - 1); }
> + /* If the bit is set, extend c1 with its value. */
> + (if (!wi::cmp (bit_value, 1, TYPE_SIGN (type)))
> + (with {
> + c1 |= wi::mask (rest_bits, true, TYPE_PRECISION (type));
> + tree c1_ext = wide_int_to_tree (type, c1); }
> + (mult (plus @0 { c1_ext; }) @2))))))))
>
> #if GIMPLE
> /* Canonicalize X + (X << C) into X * (1 + (1 << C)) and
> diff --git a/gcc/testsuite/gcc.target/i386/pr116845.c
> b/gcc/testsuite/gcc.target/i386/pr116845.c
> new file mode 100644
> index 00000000000..230e4d5f8b5
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/pr116845.c
> @@ -0,0 +1,23 @@
> +/* PR tree-optimization/116845 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-optimized -m32" } */
> +
> +int foo(int *a, int j)
> +{
> + int k = j - 1;
> + return a[j - 1] == a[k];
> +}
> +
> +int foo2(int *a, int j)
> +{
> + int k = j - 5;
> + return a[j - 5] == a[k];
> +}
> +
> +int bar(int *a, int j)
> +{
> + int k = j - 1;
> + return (&a[j + 1] - 2) == &a[k];
> +}
> +
> +/* { dg-final { scan-tree-dump-times "return 1;" 3 "optimized" } } */
> --
> 2.47.0
>
