RFC patch for fold-const.c's fold_indirect_ref_1 / avoid type-checking ICE with TYPE_MIN_VALUE vs. offset signess mismatches

[Tobias Burnus]

I run into the following issue on the Fortran-Dev branch. I get an ICE due to a 
tree-checking assert for fold-const.c's fold_indirect_ref_1, which has

              tree min_val = size_zero_node;
              if (type_domain && TYPE_MIN_VALUE (type_domain))
                min_val = TYPE_MIN_VALUE (type_domain);
              op01 = size_binop_loc (loc, EXACT_DIV_EXPR, op01,
                                     TYPE_SIZE_UNIT (type));
              op01 = size_binop_loc (loc, PLUS_EXPR, op01, min_val);

The problem is that "op01" is unsigned (size_type_node) while "min_val" alias 
TYPE_MIN_VALUE is signed (gfc_array_index_type which is PTRDIFF_TYPE).


TYPE_MIN_VALUE gets set via tree.c's build_range_type_1, which has:

  TYPE_MIN_VALUE (itype) = fold_convert (type, lowval);
  TYPE_MAX_VALUE (itype) = highval ? fold_convert (type, highval) : NULL;


And "op01" becomes a size_type_node via tree.h's

fold_build_pointer_plus_loc (location_t loc, tree ptr, tree off)
{
  return fold_build2_loc (loc, POINTER_PLUS_EXPR, TREE_TYPE (ptr),
                          ptr, fold_convert_loc (loc, sizetype, off));


I am not completely sure what's the best way to solve that, but the attached 
patch avoids the ICE for me.

I did an all-all language bootstrap (all,ada,go,objc,obj-c++) and had no new 
failures with regresting.
OK? Or do you have a better idea how to solve this?

Tobias

2013-05-10  Tobias Burnus  <bur...@net-b.de>

	* fold-const.c (fold_indirect_ref_1): Fold offset
	to TREE_TYPE (min_val) before converting to array syntax.

diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index 74b451e..8ac873a 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -16591,10 +16591,11 @@ fold_indirect_ref_1 (location_t loc, tree type, tree op0)
 	      tree min_val = size_zero_node;
 	      if (type_domain && TYPE_MIN_VALUE (type_domain))
 		min_val = TYPE_MIN_VALUE (type_domain);
 	      op01 = size_binop_loc (loc, EXACT_DIV_EXPR, op01,
 				     TYPE_SIZE_UNIT (type));
+             op01 = fold_convert (TREE_TYPE (min_val), op01);
 	      op01 = size_binop_loc (loc, PLUS_EXPR, op01, min_val);
 	      return build4_loc (loc, ARRAY_REF, type, op00, op01,
 				 NULL_TREE, NULL_TREE);
 	    }
 	}