On Tue, Apr 02, 2013 at 01:52:16PM +0200, Richard Biener wrote:
> in all relevant cases operand zero of the MEM_REFs are SSA names
> and thus can be compared for equality using == (exception are
> integer constant pointers where the type could be theoretically
> different).
...
Here is what I've committed to trunk after another bootstrap/regtest:
2013-04-02 Jakub Jelinek <ja...@redhat.com>
PR c++/34949
* tree-ssa-alias.c (stmt_kills_ref_p_1): If base != ref->base
and both of them are MEM_REFs, just compare first argument for
equality and attempt to deal even with differing offsets.
--- gcc/tree-ssa-alias.c.jj 2013-03-18 12:16:59.000000000 +0100
+++ gcc/tree-ssa-alias.c 2013-03-27 17:09:28.230216081 +0100
@@ -1870,20 +1870,50 @@ stmt_kills_ref_p_1 (gimple stmt, ao_ref
&& !stmt_can_throw_internal (stmt))
{
tree base, lhs = gimple_get_lhs (stmt);
- HOST_WIDE_INT size, offset, max_size;
+ HOST_WIDE_INT size, offset, max_size, ref_offset = ref->offset;
base = get_ref_base_and_extent (lhs, &offset, &size, &max_size);
/* We can get MEM[symbol: sZ, index: D.8862_1] here,
so base == ref->base does not always hold. */
- if (base == ref->base)
+ if (base != ref->base)
{
- /* For a must-alias check we need to be able to constrain
- the access properly. */
- if (size != -1 && size == max_size)
+ /* If both base and ref->base are MEM_REFs, only compare the
+ first operand, and if the second operand isn't equal constant,
+ try to add the offsets into offset and ref_offset. */
+ if (TREE_CODE (base) == MEM_REF && TREE_CODE (ref->base) == MEM_REF
+ && TREE_OPERAND (base, 0) == TREE_OPERAND (ref->base, 0))
{
- if (offset <= ref->offset
- && offset + size >= ref->offset + ref->max_size)
- return true;
+ if (!tree_int_cst_equal (TREE_OPERAND (base, 0),
+ TREE_OPERAND (ref->base, 0)))
+ {
+ double_int off1 = mem_ref_offset (base);
+ off1 = off1.alshift (BITS_PER_UNIT == 8
+ ? 3 : exact_log2 (BITS_PER_UNIT),
+ HOST_BITS_PER_DOUBLE_INT);
+ off1 = off1 + double_int::from_shwi (offset);
+ double_int off2 = mem_ref_offset (ref->base);
+ off2 = off2.alshift (BITS_PER_UNIT == 8
+ ? 3 : exact_log2 (BITS_PER_UNIT),
+ HOST_BITS_PER_DOUBLE_INT);
+ off2 = off2 + double_int::from_shwi (ref_offset);
+ if (off1.fits_shwi () && off2.fits_shwi ())
+ {
+ offset = off1.to_shwi ();
+ ref_offset = off2.to_shwi ();
+ }
+ else
+ size = -1;
+ }
}
+ else
+ size = -1;
+ }
+ /* For a must-alias check we need to be able to constrain
+ the access properly. */
+ if (size != -1 && size == max_size)
+ {
+ if (offset <= ref_offset
+ && offset + size >= ref_offset + ref->max_size)
+ return true;
}
}
Jakub
