https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66379
Bug ID: 66379
Summary: SCCVN doesn't handle aggregate array element accesses
very well
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: rguenth at gcc dot gnu.org
Blocks: 66142
Target Milestone: ---
struct X { int i; int j; };
struct X a[128];
int foo (int i)
{
struct X x;
x.i = i;
x.j = 0;
a[i] = x;
return a[i].i;
}
should ideally optimize to return i;
But first, FRE is confused by SRA:
<bb 2>:
_4 = &a[i_2(D)];
MEM[(struct X *)_4] = i_2(D);
MEM[(struct X *)_4 + 4B] = 0;
_6 = a[i_2(D)].i;
return _6;
and second (if SRA is disabled),
<bb 2>:
x.i = i_2(D);
x.j = 0;
a[i_2(D)] = x;
_6 = a[i_2(D)].i;
x ={v} {CLOBBER};
return _6;
the aggregate copy lookthrough code is too simple here (offset-based
stuff just bails out with variable indexes). Using stmt_kills_ref_p
helps for this case but it does not for the testcase in PR66142.
@@ -1879,7 +1895,7 @@ vn_reference_lookup_3 (ao_ref *ref, tree
|| handled_component_p (gimple_assign_rhs1 (def_stmt))))
{
tree base2;
- HOST_WIDE_INT offset2, size2, maxsize2;
+ HOST_WIDE_INT maxsize2;
int i, j;
auto_vec<vn_reference_op_s> rhs;
vn_reference_op_t vro;
@@ -1890,8 +1906,6 @@ vn_reference_lookup_3 (ao_ref *ref, tree
/* See if the assignment kills REF. */
base2 = ao_ref_base (&lhs_ref);
- offset2 = lhs_ref.offset;
- size2 = lhs_ref.size;
maxsize2 = lhs_ref.max_size;
if (maxsize2 == -1
|| (base != base2
@@ -1900,8 +1914,7 @@ vn_reference_lookup_3 (ao_ref *ref, tree
|| TREE_OPERAND (base, 0) != TREE_OPERAND (base2, 0)
|| !tree_int_cst_equal (TREE_OPERAND (base, 1),
TREE_OPERAND (base2, 1))))
- || offset2 > offset
- || offset2 + size2 < offset + maxsize)
+ || !stmt_kills_ref_p (def_stmt, ref))
return (void *)-1;
/* Find the common base of ref and the lhs. lhs_ops already
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66142
[Bug 66142] Loop is not vectorized because not sufficient support for
GOMP_SIMD_LANE
