[C++ PATCH] Fix ICEs with #pragma GCC ivdep (PR c++/79379)

[Jakub Jelinek]

Hi!

#pragma GCC ivdep can make it through into potential_constant_expression_1
as the following testcase shows.  As it is just a hint to the compiler,
I think it isn't needed to make loops with that pragma non-constexpr, so
the patch just ignores the hint for determination of what is a potential
constant expression and ditto in cxx_eval_constant_expression.  The pragma
is represented by ANNOTATE_EXPR with first operand being the condition
of the loop and second operand annot_expr_ivdep_kind.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2017-02-06  Jakub Jelinek  <ja...@redhat.com>

        PR c++/79379
        * constexpr.c (cxx_eval_constant_expression): Handle ANNOTATE_EXPR.
        (potential_constant_expression_1): Likewise.

        * g++.dg/cpp1y/constexpr-79379.C: New test.

--- gcc/cp/constexpr.c.jj       2017-02-03 23:35:37.000000000 +0100
+++ gcc/cp/constexpr.c  2017-02-06 16:00:21.903921006 +0100
@@ -4518,6 +4518,14 @@ cxx_eval_constant_expression (const cons
         *non_constant_p = true;
       return t;
 
+    case ANNOTATE_EXPR:
+      gcc_assert (tree_to_uhwi (TREE_OPERAND (t, 1)) == annot_expr_ivdep_kind);
+      r = cxx_eval_constant_expression (ctx, TREE_OPERAND (t, 0),
+                                       lval,
+                                       non_constant_p, overflow_p,
+                                       jump_target);
+      break;
+
     default:
       if (STATEMENT_CODE_P (TREE_CODE (t)))
        {
@@ -5689,6 +5697,10 @@ potential_constant_expression_1 (tree t,
        return false;
       }
 
+    case ANNOTATE_EXPR:
+      gcc_assert (tree_to_uhwi (TREE_OPERAND (t, 1)) == annot_expr_ivdep_kind);
+      return RECUR (TREE_OPERAND (t, 0), rval);
+
     default:
       if (objc_is_property_ref (t))
        return false;
--- gcc/testsuite/g++.dg/cpp1y/constexpr-79379.C.jj     2017-02-06 
16:09:30.457863715 +0100
+++ gcc/testsuite/g++.dg/cpp1y/constexpr-79379.C        2017-02-06 
16:08:49.000000000 +0100
@@ -0,0 +1,19 @@
+// PR c++/79379
+// { dg-do compile { target c++14 } }
+// { dg-options "-O2" }
+
+template <int N>
+constexpr int
+foo (int x)
+{
+  int q[64] = { 0 }, r = 0;
+#pragma GCC ivdep
+  for (int i = 0; i < x; ++i)
+    q[i] += 2;
+  for (int i = 0; i < x; ++i)
+    r += q[i];
+  return r + N;
+}
+
+constexpr int a = foo<0> (17);
+static_assert (a == 34, "");

        Jakub