Re: [PATCH] c++: Don't clear TREE_READONLY for -fmerge-all-constants for non-aggregates [PR107558]

[Jason Merrill via Gcc-patches]

On 11/24/22 04:13, Jakub Jelinek wrote:

Hi!

The following testcase ICEs, because OpenMP lowering for shared clause
on l variable with REFERENCE_TYPE creates POINTER_TYPE to REFERENCE_TYPE.
The reason is that the automatic variable has non-trivial construction
(reference to a lambda) and -fmerge-all-constants is on and so TREE_READONLY
isn't set - omp-low will handle automatic TREE_READONLY vars in shared
specially and only copy to the construct and not back, while !TREE_READONLY
are assumed to be changeable.
The PR91529 change rationale was that the gimplification can change
some non-addressable automatic variables to TREE_STATIC with
-fmerge-all-constants and therefore TREE_READONLY on them is undesirable.
But, the gimplifier does that only for aggregate variables:
   switch (TREE_CODE (type))
     {
     case RECORD_TYPE:
     case UNION_TYPE:
     case QUAL_UNION_TYPE:
     case ARRAY_TYPE:
and not for anything else.  So, I think clearing TREE_READONLY for
automatic integral or reference or pointer etc. vars for
-fmerge-all-constants only is unnecessary.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

OK.

2022-11-24  Jakub Jelinek  <ja...@redhat.com>

        PR c++/107558
        * decl.cc (cp_finish_decl): Don't clear TREE_READONLY on
        automatic non-aggregate variables just because of
        -fmerge-all-constants.

        * g++.dg/gomp/pr107558.C: New test.

--- gcc/cp/decl.cc.jj   2022-11-19 09:21:14.662439877 +0100
+++ gcc/cp/decl.cc      2022-11-23 13:12:31.866553152 +0100
@@ -8679,8 +8679,10 @@ cp_finish_decl (tree decl, tree init, bo

if (var_definition_p

          /* With -fmerge-all-constants, gimplify_init_constructor
-            might add TREE_STATIC to the variable.  */
-         && (TREE_STATIC (decl) || flag_merge_constants >= 2))
+            might add TREE_STATIC to aggregate variables.  */
+         && (TREE_STATIC (decl)
+             || (flag_merge_constants >= 2
+                 && AGGREGATE_TYPE_P (type))))
        {
          /* If a TREE_READONLY variable needs initialization
             at runtime, it is no longer readonly and we need to
--- gcc/testsuite/g++.dg/gomp/pr107558.C.jj     2022-11-23 13:13:27.260736525 
+0100
+++ gcc/testsuite/g++.dg/gomp/pr107558.C        2022-11-23 13:15:22.271041005 
+0100
@@ -0,0 +1,14 @@
+// PR c++/107558
+// { dg-do compile { target c++11 } }
+// { dg-additional-options "-fmerge-all-constants" }
+// { dg-additional-options "-flto" { target lto } }
+
+int a = 15;
+
+void
+foo ()
+{
+  auto &&l = [&]() { return a; };
+#pragma omp target parallel
+  l ();
+}

        Jakub