[WIP C++ PATCH] P0217R3 - C++17 structured bindings

[Jason Merrill]

On Wed, Nov 9, 2016 at 7:24 AM, Jakub Jelinek <jakub@redhat.com> wrote:
> The match.pd hunk is needed, otherwise the generic folding happily folds
> int arr[2];
> ...
> auto [ x, y ] = arr;
> &x == &arr[0]
> into 0, because it thinks x and arr are distinct VAR_DECLs.  Though, if
> such comparisons are required to be folded in constexpr contexts under
> certain conditions, we'd need to handle the DECL_VALUE_EXPRs in constexpr.c
> somehow.

What do you think of this approach instead?
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commit 7aa4bc14bdd8f01937ce2dc148722f0468d66d1b
Author: Jason Merrill <jason@redhat.com>
Date:   Sun Nov 13 19:17:40 2016 -0500

    addr_base

diff --git a/gcc/match.pd b/gcc/match.pd
index 79a418f..29ddcd8 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -2547,15 +2547,8 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
     (with
      {
        int equal = 2;
-       /* Punt in GENERIC on variables with value expressions;
-	  the value expressions might point to fields/elements
-	  of other vars etc.  */
-       if (GENERIC
-	   && ((VAR_P (base0) && DECL_HAS_VALUE_EXPR_P (base0))
-	       || (VAR_P (base1) && DECL_HAS_VALUE_EXPR_P (base1))))
-	 ;
-       else if (decl_in_symtab_p (base0)
-		&& decl_in_symtab_p (base1))
+       if (decl_in_symtab_p (base0)
+	   && decl_in_symtab_p (base1))
          equal = symtab_node::get_create (base0)
 	           ->equal_address_to (symtab_node::get_create (base1));
        else if ((DECL_P (base0)
diff --git a/gcc/tree-dfa.c b/gcc/tree-dfa.c
index 0396feb..0a8523b 100644
--- a/gcc/tree-dfa.c
+++ b/gcc/tree-dfa.c
@@ -673,6 +673,15 @@ get_addr_base_and_unit_offset_1 (tree exp, HOST_WIDE_INT *poffset,
     {
       switch (TREE_CODE (exp))
 	{
+	case VAR_DECL:
+	  if (DECL_HAS_VALUE_EXPR_P (exp))
+	    {
+	      exp = DECL_VALUE_EXPR (exp);
+	      continue;
+	    }
+	  else
+	    goto done;
+
 	case BIT_FIELD_REF:
 	  {
 	    HOST_WIDE_INT this_off = TREE_INT_CST_LOW (TREE_OPERAND (exp, 2));