Introduce ssa_defined_default_def_p function (PR tree-optimization/79529).

2017-02-17  Martin Liska  <mliska@suse.cz>

	PR tree-optimization/79529
	* tree-ssa-loop-unswitch.c (is_maybe_undefined): Use
	ssa_defined_default_def_p to handle cases which are implicitly
	defined.
	* tree-ssa.c (ssa_defined_default_def_p): New function.
	(ssa_undefined_value_p): Use ssa_defined_default_def_p to handle cases
	which are implicitly defined.
	* tree-ssa.h (ssa_defined_default_def_p): Declare.

From-SVN: r245530

1 files changed, 19 insertions, 7 deletions

diff --git a/gcc/tree-ssa.c b/gcc/tree-ssa.c
index 28020b0..831fd61 100644
--- a/gcc/tree-ssa.c
+++ b/gcc/tree-ssa.c
@@ -1251,27 +1251,39 @@ tree_ssa_strip_useless_type_conversions (tree exp)
   return exp;
 }
 
-
-/* Return true if T, an SSA_NAME, has an undefined value.  PARTIAL is what
-   should be returned if the value is only partially undefined.  */
+/* Return true if T, as SSA_NAME, has an implicit default defined value.  */
 
 bool
-ssa_undefined_value_p (tree t, bool partial)
+ssa_defined_default_def_p (tree t)
 {
-  gimple *def_stmt;
   tree var = SSA_NAME_VAR (t);
 
   if (!var)
     ;
   /* Parameters get their initial value from the function entry.  */
   else if (TREE_CODE (var) == PARM_DECL)
-    return false;
+    return true;
   /* When returning by reference the return address is actually a hidden
      parameter.  */
   else if (TREE_CODE (var) == RESULT_DECL && DECL_BY_REFERENCE (var))
-    return false;
+    return true;
   /* Hard register variables get their initial value from the ether.  */
   else if (VAR_P (var) && DECL_HARD_REGISTER (var))
+    return true;
+
+  return false;
+}
+
+
+/* Return true if T, an SSA_NAME, has an undefined value.  PARTIAL is what
+   should be returned if the value is only partially undefined.  */
+
+bool
+ssa_undefined_value_p (tree t, bool partial)
+{
+  gimple *def_stmt;
+
+  if (ssa_defined_default_def_p (t))
     return false;
 
   /* The value is undefined iff its definition statement is empty.  */