On Wed, 28 Aug 2024, Richard Biener wrote:
> When evaluating the difference of two aligned pointers in CCP we
> fail to handle the EXACT_DIV_EXPR by the element size that occurs.
> The testcase then also exercises modulo to test alignment but
> modulo by a power-of-two isn't handled either.
>
> Re-bootstrap and regtest running on x86_64-unknown-linux-gnu after
> an adjustment. I'd appreciate a second eye.
Now pushed as r15-3548-ge7d5b9aa021f6f after re-testing on
x86_64-unknown-linux-gnu.
Richard.
> Thanks,
> Richard.
>
> PR tree-optimization/116514
> * tree-ssa-ccp.cc (bit_value_binop): Handle EXACT_DIV_EXPR
> like TRUNC_DIV_EXPR. Handle exact division of a signed value
> by a power-of-two like a shift. Handle unsigned division by
> a power-of-two like a shift.
> Handle unsigned TRUNC_MOD_EXPR by power-of-two, handle signed
> TRUNC_MOD_EXPR by power-of-two if the result is zero.
>
> * gcc.dg/tree-ssa/ssa-ccp-44.c: New testcase.
> ---
> gcc/testsuite/gcc.dg/tree-ssa/ssa-ccp-44.c | 13 +++++++++++
> gcc/tree-ssa-ccp.cc | 27 +++++++++++++++++++++-
> 2 files changed, 39 insertions(+), 1 deletion(-)
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-ccp-44.c
>
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-ccp-44.c
> b/gcc/testsuite/gcc.dg/tree-ssa/ssa-ccp-44.c
> new file mode 100644
> index 00000000000..f1f09bfb117
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-ccp-44.c
> @@ -0,0 +1,13 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O -fdump-tree-ccp1" } */
> +
> +int
> +test(int* a, int* b)
> +{
> + __INTPTR_TYPE__ delta = (int*)__builtin_assume_aligned(b, 32)
> + - (int*)__builtin_assume_aligned(a, 32);
> + __INTPTR_TYPE__ x = delta % 8;
> + return (x == 0);
> +}
> +
> +/* { dg-final { scan-tree-dump "return 1;" "ccp1" } } */
> diff --git a/gcc/tree-ssa-ccp.cc b/gcc/tree-ssa-ccp.cc
> index 44711018e0e..8cd45545763 100644
> --- a/gcc/tree-ssa-ccp.cc
> +++ b/gcc/tree-ssa-ccp.cc
> @@ -1921,6 +1921,27 @@ bit_value_binop (enum tree_code code, signop sgn, int
> width,
> {
> widest_int r1max = r1val | r1mask;
> widest_int r2max = r2val | r2mask;
> + if (r2mask == 0)
> + {
> + widest_int shift = wi::exact_log2 (r2val);
> + if (shift != -1)
> + {
> + // Handle modulo by a power of 2 as a bitwise and.
> + widest_int tem_val, tem_mask;
> + bit_value_binop (BIT_AND_EXPR, sgn, width, &tem_val, &tem_mask,
> + r1type_sgn, r1type_precision, r1val, r1mask,
> + r2type_sgn, r2type_precision,
> + r2val - 1, r2mask);
> + if (sgn == UNSIGNED
> + || !wi::neg_p (r1max)
> + || (tem_mask == 0 && tem_val == 0))
> + {
> + *val = tem_val;
> + *mask = tem_mask;
> + return;
> + }
> + }
> + }
> if (sgn == UNSIGNED
> || (!wi::neg_p (r1max) && !wi::neg_p (r2max)))
> {
> @@ -1949,11 +1970,15 @@ bit_value_binop (enum tree_code code, signop sgn, int
> width,
> }
> break;
>
> + case EXACT_DIV_EXPR:
> case TRUNC_DIV_EXPR:
> {
> widest_int r1max = r1val | r1mask;
> widest_int r2max = r2val | r2mask;
> - if (r2mask == 0 && !wi::neg_p (r1max))
> + if (r2mask == 0
> + && (code == EXACT_DIV_EXPR
> + || sgn == UNSIGNED
> + || !wi::neg_p (r1max)))
> {
> widest_int shift = wi::exact_log2 (r2val);
> if (shift != -1)
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
