re PR tree-optimization/51624 (Assert_Failure atree.adb:808 during stage 3)

	PR tree-optimization/51624
	* tree-sra.c (build_ref_for_model): When replicating a chain of
	COMPONENT_REFs, stop as soon as the offset would become negative.

From-SVN: r182889

gcc/ChangeLog

+2012-01-04  Eric Botcazou  <ebotcazou@adacore.com>
+
+	PR tree-optimization/51624
+	* tree-sra.c (build_ref_for_model): When replicating a chain of
+	COMPONENT_REFs, stop as soon as the offset would become negative.
+
 2012-01-04  Jakub Jelinek  <jakub@redhat.com>
 
 	PR debug/51695

gcc/tree-sra.c

@@ -1520,11 +1520,16 @@ build_ref_for_model (location_t loc, tree base, HOST_WIDE_INT offset,
       do {
 	tree field = TREE_OPERAND (expr, 1);
 	tree cr_offset = component_ref_field_offset (expr);
-	gcc_assert (cr_offset && host_integerp (cr_offset, 1));
+	HOST_WIDE_INT bit_pos
+	  = tree_low_cst (cr_offset, 1) * BITS_PER_UNIT
+	      + TREE_INT_CST_LOW (DECL_FIELD_BIT_OFFSET (field));
 
-	offset -= TREE_INT_CST_LOW (cr_offset) * BITS_PER_UNIT;
-	offset -= TREE_INT_CST_LOW (DECL_FIELD_BIT_OFFSET (field));
+	/* We can be called with a model different from the one associated
+	   with BASE so we need to avoid going up the chain too far.  */
+	if (offset - bit_pos < 0)
+	  break;
 
+	offset -= bit_pos;
 	VEC_safe_push (tree, stack, cr_stack, expr);
 
 	expr = TREE_OPERAND (expr, 0);