Currently the code rejects:
```
tmp = *a;
*b = tmp;
```
(unless *a == *b). This can be improved such that if a and b are known to
share the same base, then only reject it if they overlap; that is the
difference of the offsets (from the base) is maybe less than the size.
This fixes the testcase in comment #0 of PR 107051.
PR tree-optimization/107051
gcc/ChangeLog:
* tree-ssa-forwprop.cc (optimize_agr_copyprop_1): Allow for
memory sharing the same base if they known not to overlap over
the size.
gcc/testsuite/ChangeLog:
* gcc.dg/tree-ssa/copy-prop-aggregate-union-1.c: New test.
Signed-off-by: Andrew Pinski <[email protected]>
---
.../tree-ssa/copy-prop-aggregate-union-1.c | 24 +++++++++++++++++
gcc/tree-ssa-forwprop.cc | 27 ++++++++++++++++++-
2 files changed, 50 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/copy-prop-aggregate-union-1.c
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/copy-prop-aggregate-union-1.c
b/gcc/testsuite/gcc.dg/tree-ssa/copy-prop-aggregate-union-1.c
new file mode 100644
index 00000000000..206f6e1be55
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/copy-prop-aggregate-union-1.c
@@ -0,0 +1,24 @@
+/* { dg-do compile } */
+/* { dg-options "-O1 -fdump-tree-forwprop1-details" } */
+/* PR tree-optimization/107051 */
+
+
+union U2 {
+ unsigned f0;
+ char * f1;
+};
+
+/* Since g_284[0] and g_284[1] are known not overlap,
+ copy prop can happen. */
+union U2 g_284[2] = {{0UL},{0xC2488F72L}};
+
+int e;
+void func_1() {
+ union U2 c = {7};
+ int *d[2];
+ for (; e;)
+ *d[1] = 0;
+ g_284[0] = c = g_284[1];
+}
+
+/* { dg-final { scan-tree-dump-times "after previous" 1 "forwprop1" } } */
diff --git a/gcc/tree-ssa-forwprop.cc b/gcc/tree-ssa-forwprop.cc
index e0f25a12f34..82344f4020d 100644
--- a/gcc/tree-ssa-forwprop.cc
+++ b/gcc/tree-ssa-forwprop.cc
@@ -1455,7 +1455,32 @@ optimize_agr_copyprop_1 (gimple *stmt, gimple *use_stmt,
*/
if (!operand_equal_p (dest2, src, 0)
&& !DECL_P (dest2) && !DECL_P (src))
- return false;
+ {
+ /* If *a and *b have the same base see if
+ the offset between the two is greater than
+ or equal to the size of the type. */
+ poly_int64 offset1, offset2;
+ tree len = TYPE_SIZE_UNIT (TREE_TYPE (src));
+ if (len == NULL_TREE
+ || !tree_fits_poly_int64_p (len))
+ return false;
+ tree base1 = get_addr_base_and_unit_offset (dest2, &offset1);
+ if (!base1)
+ return false;
+ tree base2 = get_addr_base_and_unit_offset (src, &offset2);
+ if (!base2)
+ return false;
+ if (!operand_equal_p (base1, base2))
+ return false;
+ poly_int64 size = tree_to_poly_int64 (len);
+ /* Make sure [offset1, offset1 + len - 1] does
+ not overlap with [offset2, offset2 + len - 1]
+ or overlaps fully. */
+ if (!known_eq (offset2, offset1)
+ && !known_ge (offset2 - offset1, size)
+ && !known_ge (offset1 - offset2, size))
+ return false;
+ }
if (dump_file && (dump_flags & TDF_DETAILS))
{
--
2.43.0
