[PATCH] Fix PR78295

[Richard Biener]

The following fixes an unwanted uninit warning.

Bootstrapped and tested on x86_64-unknown-linxu-gnu, applied.

Richard.

2016-11-11  Richard Biener  <rguent...@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.

Index: gcc/tree-ssa-uninit.c
===================================================================
--- gcc/tree-ssa-uninit.c       (revision 242004)
+++ gcc/tree-ssa-uninit.c       (working copy)
@@ -212,6 +212,14 @@ warn_uninitialized_vars (bool warn_possi
             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),
Index: gcc/testsuite/gcc.dg/uninit-pr78295.c
===================================================================
--- gcc/testsuite/gcc.dg/uninit-pr78295.c       (revision 0)
+++ gcc/testsuite/gcc.dg/uninit-pr78295.c       (working copy)
@@ -0,0 +1,13 @@
+/* { 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;
+}