expr: Move reduce_bit_field target mode check [PR96151]

In some cases, expand_expr_real_2 prefers to use the mode of the
caller-suggested target instead of the mode of the expression when
passing values to reduce_to_bit_field_precision.  E.g.:

      else if (target == 0)
        op0 = convert_to_mode (mode, op0,
                               TYPE_UNSIGNED (TREE_TYPE
                                              (treeop0)));
      else
        {
          convert_move (target, op0,
                        TYPE_UNSIGNED (TREE_TYPE (treeop0)));
          op0 = target;
        }

where “op0” might not have “mode” for the “else” branch,
but does for all the others.

reduce_to_bit_field_precision discards the suggested target if it
has the wrong mode.  This patch moves that to expand_expr_real_2
instead (conditional on reduce_bit_field).

gcc/
	PR middle-end/96151
	* expr.c (expand_expr_real_2): When reducing bit fields,
	clear the target if it has a different mode from the expression.
	(reduce_to_bit_field_precision): Don't do that here.  Instead
	assert that the target already has the correct mode.

1 files changed, 5 insertions, 4 deletions

diff --git a/gcc/expr.c b/gcc/expr.c
index 715edae..c7c3e9f 100644
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -8664,7 +8664,9 @@ expand_expr_real_2 (sepops ops, rtx target, machine_mode tmode,
   reduce_bit_field = (INTEGRAL_TYPE_P (type)
 		      && !type_has_mode_precision_p (type));
 
-  if (reduce_bit_field && modifier == EXPAND_STACK_PARM)
+  if (reduce_bit_field
+      && (modifier == EXPAND_STACK_PARM
+	  || (target && GET_MODE (target) != mode)))
     target = 0;
 
   /* Use subtarget as the target for operand 0 of a binary operation.  */
@@ -11527,9 +11529,8 @@ reduce_to_bit_field_precision (rtx exp, rtx target, tree type)
 {
   scalar_int_mode mode = SCALAR_INT_TYPE_MODE (type);
   HOST_WIDE_INT prec = TYPE_PRECISION (type);
-  gcc_assert (GET_MODE (exp) == VOIDmode || GET_MODE (exp) == mode);
-  if (target && GET_MODE (target) != mode)
-    target = 0;
+  gcc_assert ((GET_MODE (exp) == VOIDmode || GET_MODE (exp) == mode)
+	      && (!target || GET_MODE (target) == mode));
 
   /* For constant values, reduce using wide_int_to_tree. */
   if (poly_int_rtx_p (exp))