On Wed, 29 May 2019, Jan Hubicka wrote:
> Hi,
> this is a variant of testcase I have comitted. Once Martin implements SRA
> part, we could add next variant that drops -fno-tree-sra.
>
> It seems odd that constant propagation only happens in fre3.
> I woud expect fre1 to discover this already.
> The IL before fre1 and 3 differs only by:
>
> test ()
> {
> struct foo foo;
> struct bar * barptr.0_1;
> struct foo * fooptr.1_2;
> - struct bar * barptr.2_3;
> - int _8;
> + int _7;
>
> - <bb 2> :
> + <bb 2> [local count: 1073741824]:
> foo.val = 0;
> barptr.0_1 = barptr;
> barptr.0_1->val2 = 123;
> fooptr.1_2 = fooptr;
> *fooptr.1_2 = foo;
> - barptr.2_3 = barptr;
> - _8 = barptr.2_3->val2;
> + _7 = barptr.0_1->val2;
> foo ={v} {CLOBBER};
> - return _8;
> + return _7;
>
> }
>
> Why VN is not able to optimize the barptr access and lookup through
> it at once? It looks that could potentially save some need to re-run
> GVN since it is common to store pointers to memory and use them multiple
> times to access other pointers.
This is because in the first pass we substitute the value of
barptr.2_3 (barptr.0_1) when looking up barptr.2_3->val2 and
since that happens in VNs IL we run into
ao_ref_init_from_vn_reference which does not re-build
a GENERIC tree for the access path but leaves us with NULL
ao_ref.ref -- I suppose we could put the original ref tree
in there, too, even if the pieces are "valueized", it's just
a more imprecise representation of the ref.
That helps this testcase.
Bootstrap / regtest running on x86_64-unknown-linux-gnu.
Richard.
2019-05-31 Richard Biener <rguent...@suse.de>
* tree-ssa-sccvn.c (ao_ref_init_from_vn_reference): Get original
full reference tree and record in ref->ref.
(vn_reference_lookup_3): Pass in original ref to
ao_ref_init_from_vn_reference.
(vn_reference_lookup): Likewise.
* tree-ssa-sccvn.h (ao_ref_init_from_vn_reference): Adjust prototype.
* gcc.dg/tree-ssa/alias-access-path-1.c: Scan fre1.
Index: gcc/tree-ssa-sccvn.c
===================================================================
--- gcc/tree-ssa-sccvn.c (revision 271803)
+++ gcc/tree-ssa-sccvn.c (working copy)
@@ -995,7 +995,7 @@ copy_reference_ops_from_ref (tree ref, v
bool
ao_ref_init_from_vn_reference (ao_ref *ref,
alias_set_type set, tree type,
- vec<vn_reference_op_s> ops)
+ vec<vn_reference_op_s> ops, tree orig_ref)
{
vn_reference_op_t op;
unsigned i;
@@ -1149,7 +1149,7 @@ ao_ref_init_from_vn_reference (ao_ref *r
if (base == NULL_TREE)
return false;
- ref->ref = NULL_TREE;
+ ref->ref = orig_ref;
ref->base = base;
ref->ref_alias_set = set;
if (base_alias_set != -1)
@@ -1976,7 +1976,8 @@ vn_reference_lookup_3 (ao_ref *ref, tree
{
lhs_ref_ok = ao_ref_init_from_vn_reference (&lhs_ref,
get_alias_set (lhs),
- TREE_TYPE (lhs), lhs_ops);
+ TREE_TYPE (lhs), lhs_ops,
+ lhs);
if (lhs_ref_ok
&& !refs_may_alias_p_1 (ref, &lhs_ref, true))
{
@@ -2718,7 +2719,7 @@ vn_reference_lookup (tree op, tree vuse,
Otherwise preserve the full reference for advanced TBAA. */
if (!valuezied_anything
|| !ao_ref_init_from_vn_reference (&r, vr1.set, vr1.type,
- vr1.operands))
+ vr1.operands, op))
ao_ref_init (&r, op);
if (! tbaa_p)
r.ref_alias_set = r.base_alias_set = 0;
Index: gcc/tree-ssa-sccvn.h
===================================================================
--- gcc/tree-ssa-sccvn.h (revision 271803)
+++ gcc/tree-ssa-sccvn.h (working copy)
@@ -229,7 +229,7 @@ vn_nary_op_t vn_nary_op_insert (tree, tr
vn_nary_op_t vn_nary_op_insert_pieces (unsigned int, enum tree_code,
tree, tree *, tree, unsigned int);
bool ao_ref_init_from_vn_reference (ao_ref *, alias_set_type, tree,
- vec<vn_reference_op_s> );
+ vec<vn_reference_op_s>, tree = NULL_TREE);
vec<vn_reference_op_s> vn_reference_operands_for_lookup (tree);
tree vn_reference_lookup_pieces (tree, alias_set_type, tree,
vec<vn_reference_op_s> ,
Index: gcc/testsuite/gcc.dg/tree-ssa/alias-access-path-1.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/alias-access-path-1.c (revision 271803)
+++ gcc/testsuite/gcc.dg/tree-ssa/alias-access-path-1.c (working copy)
@@ -1,5 +1,6 @@
/* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-fre3 -fno-tree-sra" } */
+/* { dg-options "-O2 -fdump-tree-fre1 -fno-tree-sra" } */
+
struct foo
{
int val;
@@ -18,4 +19,4 @@ test ()
return barptr->val2;
}
-/* { dg-final { scan-tree-dump-times "return 123" 1 "fre3"} } */
+/* { dg-final { scan-tree-dump-times "return 123" 1 "fre1"} } */
