[gcc r12-782] tree-sra: Avoid refreshing into const base decls (PR 100453)

[gcc r12-782] tree-sra: Avoid refreshing into const base decls (PR 100453)

[Martin Jambor]

https://gcc.gnu.org/g:ca9bb74a5f856ccdceb4797f18b0a4ac8f49d069

commit r12-782-gca9bb74a5f856ccdceb4797f18b0a4ac8f49d069
Author: Martin Jambor <mjambor@suse.cz>
Date:   Thu May 13 23:26:32 2021 +0200

    tree-sra: Avoid refreshing into const base decls (PR 100453)
    
    When SRA transforms an assignment where the RHS is an aggregate decl
    that it creates replacements for, the (least efficient) fallback
    method of dealing with them is to store all the replacements back into
    the original decl and then let the original assignment takes itc
    sourse.
    
    That of course should not need to be done for TREE_READONLY bases
    which cannot change contents.  The SRA code handled this situation in
    one of two necessary places but only for DECL_IN_CONSTANT_POOL const
    decls, this patch modifies both to check TREE_READONLY.
    
    gcc/ChangeLog:
    
    2021-05-12  Martin Jambor  <mjambor@suse.cz>
    
            PR tree-optimization/100453
            * tree-sra.c (sra_modify_assign): All const base accesses do not
            need refreshing, not just those from decl_pool.
            (sra_modify_assign): Do not refresh into a const base decl.
    
    gcc/testsuite/ChangeLog:
    
    2021-05-12  Martin Jambor  <mjambor@suse.cz>
    
            PR tree-optimization/100453
            * gcc.dg/tree-ssa/pr100453.c: New test.

Diff:
---
 gcc/testsuite/gcc.dg/tree-ssa/pr100453.c | 18 ++++++++++++++++++
 gcc/tree-sra.c                           |  4 ++--
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr100453.c b/gcc/testsuite/gcc.dg/tree-ssa/pr100453.c
new file mode 100644
index 00000000000..0cf0ad23815
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr100453.c
@@ -0,0 +1,18 @@
+/* { dg-do run } */
+/* { dg-options "-O1" } */
+
+struct a {
+  int b : 4;
+} d;
+static int c, e;
+static const struct a f;
+static void g(const struct a h) {
+  for (; c < 1; c++)
+    d = h;
+  e = h.b;
+  c = h.b;
+}
+int main() {
+  g(f);
+  return 0;
+}
diff --git a/gcc/tree-sra.c b/gcc/tree-sra.c
index 8dfc923ed7e..186cd62b476 100644
--- a/gcc/tree-sra.c
+++ b/gcc/tree-sra.c
@@ -4244,7 +4244,7 @@ sra_modify_assign (gimple *stmt, gimple_stmt_iterator *gsi)
       || stmt_ends_bb_p (stmt))
     {
       /* No need to copy into a constant-pool, it comes pre-initialized.  */
-      if (access_has_children_p (racc) && !constant_decl_p (racc->base))
+      if (access_has_children_p (racc) && !TREE_READONLY (racc->base))
 	generate_subtree_copies (racc->first_child, rhs, racc->offset, 0, 0,
 				 gsi, false, false, loc);
       if (access_has_children_p (lacc))
@@ -4333,7 +4333,7 @@ sra_modify_assign (gimple *stmt, gimple_stmt_iterator *gsi)
 	    }
 	  /* Restore the aggregate RHS from its components so the
 	     prevailing aggregate copy does the right thing.  */
-	  if (access_has_children_p (racc))
+	  if (access_has_children_p (racc) && !TREE_READONLY (racc->base))
 	    generate_subtree_copies (racc->first_child, rhs, racc->offset, 0, 0,
 				     gsi, false, false, loc);
 	  /* Re-load the components of the aggregate copy destination.