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Re: tidy some gimplifcation unsharing

On May 21, 2004, Richard Henderson <> wrote:

> The VA_ARG_EXPR thing is handled during gimplification elsewhere.

But that's too late.  We may have already expanded statements assuming
variables referenced within VA_ARG_EXPRs are not volatile, in which
case the stmts will fail gimple verification later.  This broke the
build of uClibc for frv-uclinux.

>         Don't mark VA_ARG_EXPRs volatile here.

Ok to revert this bit?

Actually...  There should be a comment explaining why it's there, to
avoid having someone else make the same mistake.  Ok to install this,
if it bootstraps?  I'll post a proper patch, with a ChangeLog entry,
when I'm done testing.

What I'm not sure is whether it would be reasonable to remove the
equivalent call from gimplify_expr().  What do you think?

While at that...  Is it really the case that VA_ARG_EXPR can take
arbitrarily complex lvalue expressions?  Consider, for example,
foo->bar[baz]->saved_va_list.  Shouldn't we even attempt to gimplify the
expression as an lvalue, and, while at that, do so before marking the
decls found in the expression?  I don't think we should be changing
global decls just because they happen to be mentioned in the argument
to va_arg.  Am I missing anything?

--- gimplify.c.~2.6.~	2004-05-28 01:36:45.000000000 -0300
+++ gimplify.c	2004-05-28 06:21:16.000000000 -0300
@@ -665,7 +665,19 @@ copy_if_shared_r (tree *tp, int *walk_su
   /* Otherwise, mark the tree as visited and keep looking.  */
-    TREE_VISITED (t) = 1;
+    {
+      TREE_VISITED (t) = 1;
+      if (TREE_CODE (*tp) == VA_ARG_EXPR)
+	{
+	  /* Mark any _DECL inside the operand as volatile to avoid
+	     the optimizers messing around with it. We have to do this
+	     early, otherwise we might mark a variable as volatile
+	     after we gimplify other statements that use the variable
+	     assuming it's not volatile.  */
+	  walk_tree (&TREE_OPERAND (*tp, 0), mark_decls_volatile_r,
+		     NULL, NULL);
+	}
+    }
   return NULL_TREE;

Alexandre Oliva   
Red Hat Compiler Engineer   aoliva@{,}
Free Software Evangelist  oliva@{,}

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