This adds the capability to value-numbering of treating complex
address expressions where the offset becomes invariant as equal
to a POINTER_PLUS_EXPR. This restores CSE that is now prevented
by early lowering of &MEM[ptr + CST] to a POINTER_PLUS_EXPR.
Unfortunately this regresses gcc.dg/asan/pr99673.c again.
Bootstrapped and tested on x86_64-unknown-linux-gnu - any
opinions?
Richard.
2022-01-26 Richard Biener <rguent...@suse.de>
PR tree-optimization/104162
* tree-ssa-sccvn.cc (vn_reference_lookup): Handle
&MEM[_1 + 5].a[i] like a POINTER_PLUS_EXPR if the offset
becomes invariant.
(vn_reference_insert): Likewise.
* gcc.dg/tree-ssa/ssa-fre-99.c: New testcase.
---
gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-99.c | 27 ++++++++++
gcc/tree-ssa-sccvn.cc | 62 +++++++++++++++++++++-
2 files changed, 88 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-99.c
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-99.c
b/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-99.c
new file mode 100644
index 00000000000..101d0d63f7a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-99.c
@@ -0,0 +1,27 @@
+/* { dg-do compile } */
+/* Disable FRE1 because that for the sake of __builtin_object_size
+ will not consider the equality but still valueize 'i', defeating
+ the purpose of the check. */
+/* { dg-options "-O -fdump-tree-fre3 -fdisable-tree-fre1" } */
+
+struct S { int a[4]; };
+
+int i;
+int bar (struct S *p)
+{
+ char *q = (char *)p + 4;
+ i = 1;
+ int *r = &((struct S *)p)->a[i];
+ return q == (char *)r;
+}
+int baz (struct S *p)
+{
+ i = 1;
+ int *r = &((struct S *)p)->a[i];
+ char *q = (char *)p + 4;
+ return q == (char *)r;
+}
+
+/* Verify FRE can handle valueizing &p->a[i] and value-numbering it
+ equal to a POINTER_PLUS_EXPR. */
+/* { dg-final { scan-tree-dump-times "return 1;" 2 "fre3" } } */
diff --git a/gcc/tree-ssa-sccvn.cc b/gcc/tree-ssa-sccvn.cc
index a03f0aae924..482cf372686 100644
--- a/gcc/tree-ssa-sccvn.cc
+++ b/gcc/tree-ssa-sccvn.cc
@@ -3669,6 +3669,36 @@ vn_reference_lookup (tree op, tree vuse, vn_lookup_kind
kind,
vr1.vuse = vuse_ssa_val (vuse);
vr1.operands = operands
= valueize_shared_reference_ops_from_ref (op, &valueized_anything);
+
+ /* Handle &MEM[ptr + 5].b[1].c as POINTER_PLUS_EXPR. */
+ if (operands[0].opcode == ADDR_EXPR
+ && operands.last ().opcode == SSA_NAME)
+ {
+ poly_int64 off = 0;
+ vn_reference_op_t vro;
+ unsigned i;
+ for (i = 1; operands.iterate (i, &vro); ++i)
+ {
+ if (vro->opcode == SSA_NAME)
+ break;
+ else if (known_eq (vro->off, -1))
+ break;
+ off += vro->off;
+ }
+ if (i == operands.length () - 1)
+ {
+ gcc_assert (operands[i-1].opcode == MEM_REF);
+ tree ops[2];
+ ops[0] = operands[i].op0;
+ ops[1] = wide_int_to_tree (sizetype, off);
+ tree res = vn_nary_op_lookup_pieces (2, POINTER_PLUS_EXPR,
+ TREE_TYPE (op), ops, NULL);
+ if (res)
+ return res;
+ return NULL_TREE;
+ }
+ }
+
vr1.type = TREE_TYPE (op);
ao_ref op_ref;
ao_ref_init (&op_ref, op);
@@ -3760,13 +3790,43 @@ vn_reference_insert (tree op, tree result, tree vuse,
tree vdef)
vn_reference_t vr1;
bool tem;
+ vec<vn_reference_op_s> operands
+ = valueize_shared_reference_ops_from_ref (op, &tem);
+ /* Handle &MEM[ptr + 5].b[1].c as POINTER_PLUS_EXPR. */
+ if (operands[0].opcode == ADDR_EXPR
+ && operands.last ().opcode == SSA_NAME)
+ {
+ poly_int64 off = 0;
+ vn_reference_op_t vro;
+ unsigned i;
+ for (i = 1; operands.iterate (i, &vro); ++i)
+ {
+ if (vro->opcode == SSA_NAME)
+ break;
+ else if (known_eq (vro->off, -1))
+ break;
+ off += vro->off;
+ }
+ if (i == operands.length () - 1)
+ {
+ gcc_assert (operands[i-1].opcode == MEM_REF);
+ tree ops[2];
+ ops[0] = operands[i].op0;
+ ops[1] = wide_int_to_tree (sizetype, off);
+ vn_nary_op_insert_pieces (2, POINTER_PLUS_EXPR,
+ TREE_TYPE (op), ops, result,
+ VN_INFO (result)->value_id);
+ return;
+ }
+ }
+
vr1 = XOBNEW (&vn_tables_obstack, vn_reference_s);
if (TREE_CODE (result) == SSA_NAME)
vr1->value_id = VN_INFO (result)->value_id;
else
vr1->value_id = get_or_alloc_constant_value_id (result);
vr1->vuse = vuse_ssa_val (vuse);
- vr1->operands = valueize_shared_reference_ops_from_ref (op, &tem).copy ();
+ vr1->operands = operands.copy ();
vr1->type = TREE_TYPE (op);
vr1->punned = false;
ao_ref op_ref;
--
2.31.1
