On Tue, Sep 22, 2015 at 12:45 PM, Simon Dardis <simon.dar...@imgtec.com> wrote:
> I took an attempt at addressing this through the RTL GCSE pass. This attempt
> tweaks
> mem_attrs_eq_p to return true if its comparing something like poly+8 and MEM
> [&poly + 8].
>
> Is this a more suitable approach?
I actually recently modified stmt_kills_ref_p for a similar reason...
not that I liked that vey much.
I think the more suitable approach would be to not have both forms if
they are actually equal.
Of course that's way more work.
So splitting out a function that handles sematic equality compare of
MEM_EXPR sounds good to me.
No comments on your actual implementation yet, but I think we should
do it in a way to be re-usable
by stmt_kills_ref_p.
Richard.
> Thanks,
> Simon
>
> +/* Return true if p and q reference the same location by the same name but
> + through VAR_DECL and MEM_REF. */
> +
> +static bool
> +mem_locations_match_p (const struct mem_attrs *p, const struct mem_attrs *q)
> +{
> + HOST_WIDE_INT var_offset;
> + tree var, memref;
> +
> + if (p->expr == NULL_TREE || q->expr == NULL_TREE)
> + return false;
> +
> + if (TREE_CODE (p->expr) == MEM_REF && TREE_CODE (q->expr) == VAR_DECL)
> + {
> + var = q->expr;
> + var_offset = q->offset;
> + memref = p->expr;
> + }
> + else if (TREE_CODE (q->expr) == MEM_REF && TREE_CODE (p->expr) == VAR_DECL)
> + {
> + var = p->expr;
> + var_offset = p->offset;
> + memref = q->expr;
> + }
> + else
> + return false;
> +
> + if (TREE_OPERAND (TREE_OPERAND (memref, 0), 0) != var)
> + return false;
> +
> + if (TREE_TYPE (TREE_TYPE (var)) != TREE_TYPE (memref))
> + return false;
> +
> + tree offset = TREE_OPERAND (memref, 1);
> + if ((TREE_CODE (offset) == INTEGER_CST && tree_fits_shwi_p (offset)
> + && tree_to_shwi (offset) == var_offset)
> + || offset == NULL_TREE && var_offset == 0)
> + return true;
> +
> + return false;
> +
> +}
> +
> /* Return true if the given memory attributes are equal. */
>
> bool
> @@ -254,16 +298,16 @@ mem_attrs_eq_p (const struct mem_attrs *p, const struct
> mem_attrs *q)
> return false;
> return (p->alias == q->alias
> && p->offset_known_p == q->offset_known_p
> - && (!p->offset_known_p || p->offset == q->offset)
> && p->size_known_p == q->size_known_p
> && (!p->size_known_p || p->size == q->size)
> && p->align == q->align
> && p->addrspace == q->addrspace
> - && (p->expr == q->expr
> - || (p->expr != NULL_TREE && q->expr != NULL_TREE
> - && operand_equal_p (p->expr, q->expr, 0))));
> + && (mem_locations_match_p (p, q)
> + || (!p->offset_known_p || p->offset == q->offset)
> + && (p->expr == q->expr
> + || (p->expr != NULL_TREE && q->expr != NULL_TREE
> + && operand_equal_p (p->expr, q->expr, 0)))));
> }
