[gcc r10-9650] sra: Fix bug in grp_write propagation (PR 97009)

[gcc r10-9650] sra: Fix bug in grp_write propagation (PR 97009)

[Martin Jambor]

https://gcc.gnu.org/g:368875572b6b6be75d7cc162797d07e779194fb1

commit r10-9650-g368875572b6b6be75d7cc162797d07e779194fb1
Author: Martin Jambor <mjambor@suse.cz>
Date:   Thu Apr 1 10:12:23 2021 +0200

    sra: Fix bug in grp_write propagation (PR 97009)
    
    SRA represents parts of aggregates which are arrays accessed with
    unknown index as "unscalarizable regions."  When there are two such
    regions one within another and the outer is only read whereas the
    inner is written to, SRA fails to propagate that write information
    across assignments.  This means that a second aggregate can contain
    data while SRA thinks it does not and the pass can wrongly eliminate
    big chunks of assignment from that second aggregate into a third
    aggregate, which is what happens in PR 97009.
    
    Fixed by checking all children of unscalariable accesses for the
    grp_write flag.
    
    gcc/ChangeLog:
    
    2021-03-31  Martin Jambor  <mjambor@suse.cz>
    
            PR tree-optimization/97009
            * tree-sra.c (access_or_its_child_written): New function.
            (propagate_subaccesses_from_rhs): Use it instead of a simple grp_write
            test.
    
    gcc/testsuite/ChangeLog:
    
    2021-03-31  Martin Jambor  <mjambor@suse.cz>
    
            PR tree-optimization/97009
            * gcc.dg/tree-ssa/pr97009.c: New test.
    
    (cherry picked from commit 19d71674616e6494a60432a2a28adcd762a6c877)

Diff:
---
 gcc/testsuite/gcc.dg/tree-ssa/pr97009.c | 66 +++++++++++++++++++++++++++++++++
 gcc/tree-sra.c                          | 15 +++++++-
 2 files changed, 80 insertions(+), 1 deletion(-)

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr97009.c b/gcc/testsuite/gcc.dg/tree-ssa/pr97009.c
new file mode 100644
index 00000000000..741dbc270c3
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr97009.c
@@ -0,0 +1,66 @@
+/* { dg-do run } */
+/* { dg-options "-O1" } */
+
+static int __attribute__((noipa))
+get_5 (void)
+{
+  return 5;
+}
+
+static int __attribute__((noipa))
+verify_5 (int v)
+{
+  if (v != 5)
+    __builtin_abort ();
+}
+
+struct T
+{
+  int w;
+  int a[4];
+};
+
+struct S
+{
+  int v;
+  int x;
+  struct T t[2];
+  char alotofstuff[128];
+};
+
+volatile int vol;
+
+void __attribute__((noipa))
+consume_t (struct T t)
+{
+  vol = t.a[0];
+}
+
+int __attribute__((noipa))
+foo (int l1, int l2)
+{
+  struct S s1, s2, s3;
+  int i, j;
+
+  s1.v = get_5 ();
+  for (i = 0; i < l1; i++)
+    {
+      for (j = 0; j < l2; j++)
+	s1.t[i].a[j] = get_5 ();
+      consume_t(s1.t[i]);
+    }
+
+  s2 = s1;
+
+  s3 = s2;
+  for (i = 0; i < l1; i++)
+    for (j = 0; j < l2; j++)
+      verify_5 (s3.t[i].a[j]);
+}
+
+int
+main (int argc, char *argv[])
+{
+  foo (2, 4);
+  return 0;
+}
diff --git a/gcc/tree-sra.c b/gcc/tree-sra.c
index 4d622d9ea3d..85b9cc9ed7f 100644
--- a/gcc/tree-sra.c
+++ b/gcc/tree-sra.c
@@ -2729,6 +2729,19 @@ budget_for_propagation_access (tree decl)
   return true;
 }
 
+/* Return true if ACC or any of its subaccesses has grp_child set.  */
+
+static bool
+access_or_its_child_written (struct access *acc)
+{
+  if (acc->grp_write)
+    return true;
+  for (struct access *sub = acc->first_child; sub; sub = sub->next_sibling)
+    if (access_or_its_child_written (sub))
+      return true;
+  return false;
+}
+
 /* Propagate subaccesses and grp_write flags of RACC across an assignment link
    to LACC.  Enqueue sub-accesses as necessary so that the write flag is
    propagated transitively.  Return true if anything changed.  Additionally, if
@@ -2836,7 +2849,7 @@ propagate_subaccesses_from_rhs (struct access *lacc, struct access *racc)
       if (rchild->grp_unscalarizable_region
 	  || !budget_for_propagation_access (lacc->base))
 	{
-	  if (rchild->grp_write && !lacc->grp_write)
+	  if (!lacc->grp_write && access_or_its_child_written (rchild))
 	    {
 	      ret = true;
 	      subtree_mark_written_and_rhs_enqueue (lacc);