re PR middle-end/78295 (Spurious -Wuninitialized warning for vector element assignment)

2016-11-11  Richard Biener  <rguenther@suse.de>

	PR middle-end/78295
	* tree-ssa-uninit.c (warn_uninitialized_vars): Do not warn
	about uninitialized destination arg of BIT_INSERT_EXPR.

	* gcc.dg/uninit-pr78295.c: New testcase.

From-SVN: r242068

gcc/ChangeLog

+2016-11-11  Richard Biener  <rguenther@suse.de>
+
+	PR middle-end/78295
+	* tree-ssa-uninit.c (warn_uninitialized_vars): Do not warn
+	about uninitialized destination arg of BIT_INSERT_EXPR.
+
 2016-11-10  Sandra Loosemore  <sandra@codesourcery.com>
 
 	PR c/37998

gcc/testsuite/ChangeLog

+2016-11-11  Richard Biener  <rguenther@suse.de>
+
+	PR middle-end/78295
+	* gcc.dg/uninit-pr78295.c: New testcase.
+
 2016-11-10  Fritz O. Reese <fritzoreese@gmail.com>
 
 	PR fortran/78277

gcc/testsuite/gcc.dg/uninit-pr78295.c

+/* { dg-do compile } */
+/* { dg-options "-O2 -Wall" } */
+
+typedef double vectype __attribute__ ((__vector_size__ (16)));
+
+vectype
+f (double x)
+{
+  vectype t;
+  for (int i = 0; i < 2; i++)
+    t[i] = x; /* { dg-bogus "uninitialized" } */
+  return t;
+}

gcc/tree-ssa-uninit.c

@@ -212,6 +212,14 @@ warn_uninitialized_vars (bool warn_possibly_uninitialized)
 	     can warn about.  */
 	  FOR_EACH_SSA_USE_OPERAND (use_p, stmt, op_iter, SSA_OP_USE)
 	    {
+	      /* BIT_INSERT_EXPR first operand should not be considered
+	         a use for the purpose of uninit warnings.  */
+	      if (gassign *ass = dyn_cast <gassign *> (stmt))
+		{
+		  if (gimple_assign_rhs_code (ass) == BIT_INSERT_EXPR
+		      && use_p->use == gimple_assign_rhs1_ptr (ass))
+		    continue;
+		}
 	      use = USE_FROM_PTR (use_p);
 	      if (always_executed)
 		warn_uninit (OPT_Wuninitialized, use, SSA_NAME_VAR (use),