[Ada] Fix wrong debug info for variant record

[Ada] Fix wrong debug info for variant record

[Eric Botcazou]

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This is a regression present on the mainline and 6 branch whereby the compiler 
generates an incorrect GNAT encoding in the debug info for a variant record.

Tested on x86_64-suse-linux, applied on mainline and 6 branch.


2017-02-24  Eric Botcazou  <ebotcazou@adacore.com>

	* gcc-interface/utils.c (fold_bit_position): New function.
	(rest_of_record_type_compilation): Call it instead of bit_position to
	compute the field position and remove the call to remove_conversions.
	(compute_related_constant): Factor out the multiplication in both
	operands, if any, and streamline the final test.

-- 
Eric Botcazou

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Index: gcc-interface/utils.c
===================================================================
--- gcc-interface/utils.c	(revision 245698)
+++ gcc-interface/utils.c	(working copy)
@@ -238,6 +238,7 @@ static GTY ((cache))
   hash_table<pad_type_hasher> *pad_type_hash_table;
 
 static tree merge_sizes (tree, tree, tree, bool, bool);
+static tree fold_bit_position (const_tree);
 static tree compute_related_constant (tree, tree);
 static tree split_plus (tree, tree *);
 static tree float_type_for_precision (int, machine_mode);
@@ -2041,15 +2042,11 @@ rest_of_record_type_compilation (tree re
 	{
 	  tree field_type = TREE_TYPE (old_field);
 	  tree field_name = DECL_NAME (old_field);
-	  tree curpos = bit_position (old_field);
+	  tree curpos = fold_bit_position (old_field);
 	  tree pos, new_field;
 	  bool var = false;
 	  unsigned int align = 0;
 
-	  /* We're going to do some pattern matching below so remove as many
-	     conversions as possible.  */
-	  curpos = remove_conversions (curpos, true);
-
 	  /* See how the position was modified from the last position.
 
 	     There are two basic cases we support: a value was added
@@ -2146,7 +2143,7 @@ rest_of_record_type_compilation (tree re
 	     is when there are other components at fixed positions after
 	     it (meaning there was a rep clause for every field) and we
 	     want to be able to encode them.  */
-	  last_pos = size_binop (PLUS_EXPR, bit_position (old_field),
+	  last_pos = size_binop (PLUS_EXPR, curpos,
 				 (TREE_CODE (TREE_TYPE (old_field))
 				  == QUAL_UNION_TYPE)
 				 ? bitsize_zero_node
@@ -2201,23 +2198,51 @@ merge_sizes (tree last_size, tree first_
   return new_size;
 }
 
+/* Return the bit position of FIELD, in bits from the start of the record,
+   and fold it as much as possible.  This is a tree of type bitsizetype.  */
+
+static tree
+fold_bit_position (const_tree field)
+{
+  tree offset = DECL_FIELD_OFFSET (field);
+  if (TREE_CODE (offset) == MULT_EXPR || TREE_CODE (offset) == PLUS_EXPR)
+    offset = size_binop (TREE_CODE (offset),
+			 fold_convert (bitsizetype, TREE_OPERAND (offset, 0)),
+			 fold_convert (bitsizetype, TREE_OPERAND (offset, 1)));
+  else
+    offset = fold_convert (bitsizetype, offset);
+  return size_binop (PLUS_EXPR, DECL_FIELD_BIT_OFFSET (field),
+ 		     size_binop (MULT_EXPR, offset, bitsize_unit_node));
+}
+
 /* Utility function of above to see if OP0 and OP1, both of SIZETYPE, are
    related by the addition of a constant.  Return that constant if so.  */
 
 static tree
 compute_related_constant (tree op0, tree op1)
 {
-  tree op0_var, op1_var;
-  tree op0_con = split_plus (op0, &op0_var);
-  tree op1_con = split_plus (op1, &op1_var);
-  tree result = size_binop (MINUS_EXPR, op0_con, op1_con);
+  tree factor, op0_var, op1_var, op0_cst, op1_cst, result;
 
-  if (operand_equal_p (op0_var, op1_var, 0))
-    return result;
-  else if (operand_equal_p (op0, size_binop (PLUS_EXPR, op1_var, result), 0))
-    return result;
+  if (TREE_CODE (op0) == MULT_EXPR
+      && TREE_CODE (op1) == MULT_EXPR
+      && TREE_CODE (TREE_OPERAND (op0, 1)) == INTEGER_CST
+      && TREE_OPERAND (op1, 1) == TREE_OPERAND (op0, 1))
+    {
+      factor = TREE_OPERAND (op0, 1);
+      op0 = TREE_OPERAND (op0, 0);
+      op1 = TREE_OPERAND (op1, 0);
+    }
   else
-    return 0;
+    factor = NULL_TREE;
+
+  op0_cst = split_plus (op0, &op0_var);
+  op1_cst = split_plus (op1, &op1_var);
+  result = size_binop (MINUS_EXPR, op0_cst, op1_cst);
+
+  if (operand_equal_p (op0_var, op1_var, 0))
+    return factor ? size_binop (MULT_EXPR, factor, result) : result;
+
+  return NULL_TREE;
 }
 
 /* Utility function of above to split a tree OP which may be a sum, into a