[gcc r11-10144] tree-sra: Fix union handling in build_reconstructed_reference

[gcc r11-10144] tree-sra: Fix union handling in build_reconstructed_reference

[Martin Jambor]

https://gcc.gnu.org/g:16afe2e2862f3dd93c711d7f8d436dee23c6c34d

commit r11-10144-g16afe2e2862f3dd93c711d7f8d436dee23c6c34d
Author: Martin Jambor <mjambor@suse.cz>
Date:   Tue Jul 12 13:16:35 2022 +0200

    tree-sra: Fix union handling in build_reconstructed_reference
    
    As the testcase in PR 105860 shows, the code that tries to re-use the
    handled_component chains in SRA can be horribly confused by unions,
    where it thinks it has found a compatible structure under which it can
    chain the references, but in fact it found the type it was looking
    for elsewhere in a union and generated a write to a completely wrong
    part of an aggregate.
    
    I don't remember whether the plan was to support unions at all in
    build_reconstructed_reference but it can work, to an extent, if we
    make sure that we start the search only outside the outermost union,
    which is what the patch does (and the extra testcase verifies).
    
    Additionally, this commit also contains sqashed in it a backport of
    b984b84cbe4bf026edef2ba37685f3958a1dc1cf which fixes the testcase
    gcc.dg/tree-ssa/alias-access-path-13.c for many 32-bit targets.
    
    gcc/ChangeLog:
    
    2022-07-01  Martin Jambor  <mjambor@suse.cz>
    
            PR tree-optimization/105860
            * tree-sra.c (build_reconstructed_reference): Start expr
            traversal only just below the outermost union.
    
    gcc/testsuite/ChangeLog:
    
    2022-07-01  Martin Jambor  <mjambor@suse.cz>
    
            PR tree-optimization/105860
            * gcc.dg/tree-ssa/alias-access-path-13.c: New test.
            * gcc.dg/tree-ssa/pr105860.c: Likewise.
    
    (cherry picked from commit b110e5283e368b5377e04766e4ff82cd52634208)

Diff:
---
 .../gcc.dg/tree-ssa/alias-access-path-13.c         | 36 +++++++++++++
 gcc/testsuite/gcc.dg/tree-ssa/pr105860.c           | 63 ++++++++++++++++++++++
 gcc/tree-sra.c                                     | 13 ++++-
 3 files changed, 111 insertions(+), 1 deletion(-)

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/alias-access-path-13.c b/gcc/testsuite/gcc.dg/tree-ssa/alias-access-path-13.c
new file mode 100644
index 00000000000..87a94f5bf31
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/alias-access-path-13.c
@@ -0,0 +1,36 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-fre1" } */
+
+struct inn
+{
+  int val;
+};
+
+struct biggerstruct
+{
+  int a, b;
+};
+
+union foo
+{
+  struct inn inn;
+  struct biggerstruct baz;
+} *fooptr;
+
+struct bar
+{
+  union foo foo;
+  int val2;
+} *barptr;
+
+int
+test ()
+{
+  union foo foo;
+  foo.inn.val = 0;
+  barptr->val2 = 123;
+  *fooptr = foo;
+  return barptr->val2;
+}
+
+/* { dg-final { scan-tree-dump-times "return 123" 1 "fre1"} } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr105860.c b/gcc/testsuite/gcc.dg/tree-ssa/pr105860.c
new file mode 100644
index 00000000000..77bcb4a6739
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr105860.c
@@ -0,0 +1,63 @@
+/* { dg-do run } */
+/* { dg-options "-O1" } */
+
+struct S1  {
+        unsigned int _0;
+        unsigned int _1;
+} ;
+struct S2  {
+        struct S1 _s1;
+        unsigned long _x2;
+} ;
+
+struct ufld_type1  {
+        unsigned int _u1t;
+        struct S2 _s2;
+} ;
+
+struct ufld_type2  {
+        unsigned int _u2t;
+        struct S1 _s1;
+} ;
+struct parm_type {
+        union {
+                struct ufld_type1 var_1;
+                struct ufld_type2 var_2;
+        } U;
+};
+
+struct parm_type  bad_function( struct parm_type arg0 )
+{
+        struct parm_type rv;
+        struct S2 var4;
+        switch( arg0.U.var_2._u2t ) {
+        case 4294967041:
+                var4._s1 = arg0.U.var_1._s2._s1;
+                rv.U.var_1._u1t = 4294967041;
+                rv.U.var_1._s2 = var4;
+                break;
+        case 4294967043:
+                rv.U.var_2._u2t = 4294967043;
+                rv.U.var_2._s1 = arg0.U.var_2._s1;
+                break;
+        default:
+                break;
+        }
+        return rv;
+}
+
+int main() {
+        struct parm_type val;
+        struct parm_type out;
+        val.U.var_2._u2t = 4294967043;
+        val.U.var_2._s1._0 = 0x01010101;
+        val.U.var_2._s1._1 = 0x02020202;
+        out = bad_function(val);
+	if (val.U.var_2._u2t != 4294967043)
+	  __builtin_abort ();
+        if (out.U.var_2._s1._0 != 0x01010101)
+	  __builtin_abort ();
+        if (val.U.var_2._s1._1 != 0x02020202 )
+	  __builtin_abort ();
+	return 0;
+}
diff --git a/gcc/tree-sra.c b/gcc/tree-sra.c
index 970ad386873..dea9cf3235c 100644
--- a/gcc/tree-sra.c
+++ b/gcc/tree-sra.c
@@ -1647,7 +1647,18 @@ build_ref_for_offset (location_t loc, tree base, poly_int64 offset,
 static tree
 build_reconstructed_reference (location_t, tree base, struct access *model)
 {
-  tree expr = model->expr, prev_expr = NULL;
+  tree expr = model->expr;
+  /* We have to make sure to start just below the outermost union.  */
+  tree start_expr = expr;
+  while (handled_component_p (expr))
+    {
+      if (TREE_CODE (TREE_TYPE (TREE_OPERAND (expr, 0))) == UNION_TYPE)
+	start_expr = expr;
+      expr = TREE_OPERAND (expr, 0);
+    }
+
+  expr = start_expr;
+  tree prev_expr = NULL_TREE;
   while (!types_compatible_p (TREE_TYPE (expr), TREE_TYPE (base)))
     {
       if (!handled_component_p (expr))