[PR68083] don't introduce undefined behavior in ifcombine

The ifcombine pass may move a conditional access to an uninitialized
value before the condition that ensures it is always well-defined,
thus introducing undefined behavior.  Stop it from doing so.

for  gcc/ChangeLog

	PR tree-optimization/68083
	* tree-ssa-ifcombine.c: Include tree-ssa.h.
	(bb_no_side_effects_p): Test for undefined uses too.
	* tree-ssa.c (gimple_uses_undefined_value_p): New.
	* tree-ssa.h (gimple_uses_undefined_value_p): Declare.

for  gcc/testsuite/ChangeLog

	PR tree-optimization/68083
	* gcc.dg/torture/pr68083.c: New.  From Zhendong Su.

From-SVN: r229690

1 files changed, 18 insertions, 0 deletions

diff --git a/gcc/tree-ssa.c b/gcc/tree-ssa.c
index 20e05ad..84a4d5b 100644
--- a/gcc/tree-ssa.c
+++ b/gcc/tree-ssa.c
@@ -1203,6 +1203,24 @@ ssa_undefined_value_p (tree t, bool partial)
 }
 
 
+/* Return TRUE iff STMT, a gimple statement, references an undefined
+   SSA name.  */
+
+bool
+gimple_uses_undefined_value_p (gimple *stmt)
+{
+  ssa_op_iter iter;
+  tree op;
+
+  FOR_EACH_SSA_TREE_OPERAND (op, stmt, iter, SSA_OP_USE)
+    if (ssa_undefined_value_p (op))
+      return true;
+
+  return false;
+}
+
+
+
 /* If necessary, rewrite the base of the reference tree *TP from
    a MEM_REF to a plain or converted symbol.  */