From: Martin Jambor <mjambor@suse.cz>
Date: Wed, 23 Jul 2025 09:22:33 +0000 (+0200)
Subject: tree-sra: Avoid total SRA if there are incompat. aggregate accesses  (PR119085)
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=171fcc80ede596442712e559c4fc787aa4636694;p=thirdparty%2Fgcc.git

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.
---

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr119085.c b/gcc/testsuite/gcc.dg/tree-ssa/pr119085.c
new file mode 100644
index 00000000000..e9811ce12b5
--- /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 240af676ea3..032f2770484 100644
--- 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