[PATCH] proposed fix for bug # 61144

[Rich Felker]

Bug # 61144 is a regression in 4.9.0 that breaks building of musl libc
due to aggressive and semantically-incorrect constant folding of weak
aliases. The attached patch seems to fix the issue. A weak alias
should never be a candidate for constant folding because it may always
be replaced by a strong definition from another translation unit.

For details see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61144

I do not have a copyright assignment on file but this patch should be
sufficiently trivial not to require it.

Rich

diff --git a/gcc/varpool.c b/gcc/varpool.c
index b426757..905047e 100644
--- a/gcc/varpool.c
+++ b/gcc/varpool.c
@@ -195,6 +195,8 @@ ctor_for_folding (tree decl)
     {
       gcc_assert (!DECL_INITIAL (decl)
                  || DECL_INITIAL (decl) == error_mark_node);
+      if (DECL_WEAK (decl))
+        return error_mark_node;
       if (lookup_attribute ("weakref", DECL_ATTRIBUTES (decl)))
        {
          node = varpool_alias_target (node);