[committed] Avoid some -Wuninitialized OpenMP false positives (PR middle-end/72781)

[Jakub Jelinek]

Hi!

The control structure is too hard to understand in certain cases for the
uninit pass - the test for the last iteration compares against a specific
value, while in the loop it tests for the particular assigned chunks.

So, this patch marks the private vars for lastprivate or for simd linear
iterators as TREE_NO_WARNING.

Bootstrapped/regtested on x86_64-linux and i686-linux, committed to trunk.

2016-08-08  Jakub Jelinek  <ja...@redhat.com>

        PR middle-end/72781
        * omp-low.c (lower_lastprivate_clauses): Set TREE_NO_WARNING on the
        private vars for lastprivate and for linear iterator.

        * gcc.dg/gomp/pr72781.c: New test.

--- gcc/omp-low.c.jj    2016-07-21 18:11:00.000000000 +0200
+++ gcc/omp-low.c       2016-08-08 14:21:30.319798379 +0200
@@ -5455,7 +5455,15 @@ lower_lastprivate_clauses (tree clauses,
              new_var = lookup_decl (var, ctx->outer);
            }
          else
-           new_var = lookup_decl (var, ctx);
+           {
+             new_var = lookup_decl (var, ctx);
+             /* Avoid uninitialized warnings for lastprivate and
+                for linear iterators.  */
+             if (predicate
+                 && (OMP_CLAUSE_CODE (c) == OMP_CLAUSE_LASTPRIVATE
+                     || OMP_CLAUSE_LINEAR_NO_COPYIN (c)))
+               TREE_NO_WARNING (new_var) = 1;
+           }
 
          if (simduid && DECL_HAS_VALUE_EXPR_P (new_var))
            {
--- gcc/testsuite/gcc.dg/gomp/pr72781.c.jj      2016-08-08 14:27:09.481617344 
+0200
+++ gcc/testsuite/gcc.dg/gomp/pr72781.c 2016-08-08 14:27:50.582110675 +0200
@@ -0,0 +1,23 @@
+/* PR middle-end/72781 */
+/* { dg-do compile } */
+/* { dg-additional-options "-O2 -Wuninitialized" } */
+
+int u;
+
+void
+foo (int *p)
+{
+  int i;
+  #pragma omp for simd lastprivate(u) schedule (static, 32)    /* { dg-bogus 
"may be used uninitialized in this function" } */
+  for (i = 0; i < 1024; i++)
+    u = p[i];
+}
+
+void
+bar (int *p)
+{
+  int i;
+  #pragma omp taskloop simd lastprivate(u)     /* { dg-bogus "may be used 
uninitialized in this function" } */
+  for (i = 0; i < 1024; i++)
+    u = p[i];
+}

        Jakub