On Mon, Jun 1, 2020 at 10:37 AM Feng Xue OS via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> This patch is meant to add match rules to simplify patterns as:
>
> o. (pointer + offset_a) - (pointer + offset_b) -> (ptrdiff_t) (offset_a -
> offset_b)
> o. (pointer_a + offset) - (pointer_b + offset) -> (pointer_a - pointer_b)
You are also changing the existing pattern which IIRC tries to
preserve the undefinedness of overflow in offset_a - offset_b.
Without an explanation it's hard to guess why you think eliding
this conversion is correct.
Adding the TYPE_OVERFLOW_UNDEFINED guard also looks
odd - AFAICS overflow of the pointer type does not matter
but overflow of the generated minus? Thus at least
a || !TYPE_OVERFLOW_UNDEFINED (type) would be
in order?
Thanks,
Richard.
> Bootstrapped/regtested on x86_64-linux and aarch64-linux.
>
> Feng
> ---
> 2020-06-01 Feng Xue <f...@os.amperecomputing.com>
>
> gcc/
> PR tree-optimization/94234
> * match.pd ((PTR + A) - (PTR + B)) -> (ptrdiff_t)(A - B): New
> simplification.
> * ((PTR_A + O) - (PTR_B + O)) -> (PTR_A - PTR_B): New simplification.
>
> gcc/testsuite/
> PR tree-optimization/94234
> * gcc.dg/pr94234.c: New test.
> ---
> gcc/match.pd | 19 +++++++++----------
> gcc/testsuite/gcc.dg/pr94234.c | 24 ++++++++++++++++++++++++
> 2 files changed, 33 insertions(+), 10 deletions(-)
> create mode 100644 gcc/testsuite/gcc.dg/pr94234.c
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index 33ee1a920bf..6553be4822e 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -2515,16 +2515,15 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> && TREE_CODE (@2) == INTEGER_CST
> && tree_int_cst_sign_bit (@2) == 0))
> (minus (convert @1) (convert @2)))))
> - (simplify
> - (pointer_diff (pointer_plus @@0 @1) (pointer_plus @0 @2))
> - /* The second argument of pointer_plus must be interpreted as signed, and
> - thus sign-extended if necessary. */
> - (with { tree stype = signed_type_for (TREE_TYPE (@1)); }
> - /* Use view_convert instead of convert here, as POINTER_PLUS_EXPR
> - second arg is unsigned even when we need to consider it as signed,
> - we don't want to diagnose overflow here. */
> - (minus (convert (view_convert:stype @1))
> - (convert (view_convert:stype @2)))))))
> + (simplify
> + (pointer_diff (pointer_plus@3 @0 @1) (pointer_plus @0 @2))
> + (if (TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (@3)))
> + (convert (minus @1 @2))))
> + (simplify
> + (pointer_diff (pointer_plus@3 @0 @2) (pointer_plus @1 @2))
> + (if (TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (@3))
> + && !integer_zerop (@2))
> + (pointer_diff @0 @1)))))
>
> /* (A * C) +- (B * C) -> (A+-B) * C and (A * C) +- A -> A * (C+-1).
> Modeled after fold_plusminus_mult_expr. */
> diff --git a/gcc/testsuite/gcc.dg/pr94234.c b/gcc/testsuite/gcc.dg/pr94234.c
> new file mode 100644
> index 00000000000..ef9076c80da
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/pr94234.c
> @@ -0,0 +1,24 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-ccp1" } */
> +
> +typedef __SIZE_TYPE__ size_t;
> +typedef __PTRDIFF_TYPE__ ptrdiff_t;
> +
> +ptrdiff_t foo (char *a, size_t n)
> +{
> + char *b1 = a + 8 * n;
> + char *b2 = a + 8 * (n - 1);
> +
> + return b1 - b2;
> +}
> +
> +ptrdiff_t goo (char *a, size_t n, size_t m)
> +{
> + char *b1 = a + 8 * n;
> + char *b2 = a + 8 * (n + 1);
> +
> + return (b1 + m) - (b2 + m);
> +}
> +
> +/* { dg-final { scan-tree-dump-times "return 8;" 1 "ccp1" } } */
> +/* { dg-final { scan-tree-dump-times "return -8;" 1 "ccp1" } } */
