* cgraph.h (struct varpool_node): Add const_value_known.

	(varpool_decide_const_value_known): Declare.
	* tree-ssa-ccp.c (fold_const_aggregate_ref): Update initializer folding.
	* lto-cgraph.c (lto_output_varpool_node): Store const_value_known.
	(input_varpool_node): Restore const_value_known.
	* tree-ssa-loop-ivcanon (constant_after_peeling): Check varpool for
	initializer folding.
	* ipa.c (ipa_discover_readonly_nonaddressable_var,
	function_and_variable_visibility): Compute const_value_known.
	* gimple-fold.c (get_symbol_constant_value): Use varpool for initializer
	folding.
	* varpool.c (varpool_decide_const_value_known): New function.


git-svn-id: https://gcc.gnu.org/svn/gcc/trunk@163808 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 31 insertions, 0 deletions

diff --git a/gcc/varpool.c b/gcc/varpool.c
index 817a3197901..eac488fa79b 100644
--- a/gcc/varpool.c
+++ b/gcc/varpool.c
@@ -359,6 +359,37 @@ decide_is_variable_needed (struct varpool_node *node, tree decl)
   return true;
 }
 
+/* Return if NODE is constant and its initial value is known (so we can do
+   constant folding).  The decision depends on whole program decisions
+   and can not be recomputed at ltrans stage for variables from other
+   partitions.  For this reason the new value should be always combined
+   with the previous knowledge.  */
+
+bool
+varpool_decide_const_value_known (struct varpool_node *node)
+{
+  tree decl = node->decl;
+
+  gcc_assert (TREE_STATIC (decl) || DECL_EXTERNAL (decl));
+  gcc_assert (TREE_CODE (decl) == VAR_DECL);
+  if (!TREE_READONLY (decl))
+    return false;
+  /* Variables declared 'const' without an initializer
+     have zero as the initializer if they may not be
+     overridden at link or run time.  */
+  if (!DECL_INITIAL (decl)
+      && (DECL_EXTERNAL (decl)
+	  || DECL_REPLACEABLE_P (decl)))
+    return false;
+
+  /* Variables declared `const' with an initializer are considered
+     to not be overwritable with different initializer by default. 
+
+     ??? Previously we behaved so for scalar variables but not for array
+     accesses.  */
+  return true;
+}
+
 /* Mark DECL as finalized.  By finalizing the declaration, frontend instruct the
    middle end to output the variable to asm file, if needed or externally
    visible.  */