tree-sra: Avoid total SRA if there are incompat. aggregate accesses (PR119085)

We currently use the types encountered in the function body and not in
type declaration to perform total scalarization.  Bug PR 119085
uncovered that we miss a check that when the same data is accessed
with aggregate types that those are actually compatible.  Without it,
we can base total scalarization on a type that does not "cover" all
live data in a different part of the function.  This patch adds the
check.

gcc/ChangeLog:

2025-07-21  Martin Jambor  <mjambor@suse.cz>

	PR tree-optimization/119085
	* tree-sra.cc (sort_and_splice_var_accesses): Prevent total
	scalarization if two incompatible aggregates access the same place.

gcc/testsuite/ChangeLog:

2025-07-21  Martin Jambor  <mjambor@suse.cz>

	PR tree-optimization/119085
	* gcc.dg/tree-ssa/pr119085.c: New test.

(cherry picked from commit 171fcc80ede596442712e559c4fc787aa4636694)

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr119085.c b/gcc/testsuite/gcc.dg/tree-ssa/pr119085.c
new file mode 100644 (file)
index 0000000..e9811ce
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr119085.c
@@ -0,0 +1,37 @@
+/* { dg-do run } */
+/* { dg-options "-O1" } */
+
+struct with_hole {
+  int x;
+  long y;
+};
+struct without_hole {
+  int x;
+  int y;
+};
+union u {
+  struct with_hole with_hole;
+  struct without_hole without_hole;
+};
+
+void __attribute__((noinline))
+test (union u *up, union u u)
+{
+  union u u2;
+  volatile int f = 0;
+  u2 = u;
+  if (f)
+    u2.with_hole = u.with_hole;
+  *up = u2;
+}
+
+int main(void)
+{
+  union u u;
+  union u u2;
+  u2.without_hole.y = -1;
+  test (&u, u2);
+  if (u.without_hole.y != -1)
+    __builtin_abort ();
+  return 0;
+}

diff --git a/gcc/tree-sra.cc b/gcc/tree-sra.cc
index 307e8e29b8440e33faa53cdeb64b64e2b9fe9a17..aac5d733aa7b503706a5a9f6c6ef62ddb24bf7b4 100644 (file)
--- a/gcc/tree-sra.cc
+++ b/gcc/tree-sra.cc
@@ -2504,6 +2504,12 @@ sort_and_splice_var_accesses (tree var)
                }
              unscalarizable_region = true;
            }
+         /* If there the same place is accessed with two incompatible
+            aggregate types, trying to base total scalarization on either of
+            them can be wrong.  */
+         if (!first_scalar && !types_compatible_p (access->type, ac2->type))
+           bitmap_set_bit (cannot_scalarize_away_bitmap,
+                           DECL_UID (access->base));
 
          if (grp_same_access_path
              && (!ac2->grp_same_access_path