expr: Fix up VEC_PACK_TRUNC_EXPR expansion [PR101046]

The following testcase ICEs, because we have a mode mismatch.
VEC_PACK_TRUNC_EXPR's operands have different modes from the result
(same vector mode size but twice as large element),
but we were passing non-NULL subtarget with the mode of the result
to the expansion of its arguments, so the VEC_PERM_EXPR in one of the
operands which had V8SImode operands and result had V16HImode target.

Fixed by clearing the subtarget if we are changing mode.

2021-06-15  Jakub Jelinek  <jakub@redhat.com>

	PR target/101046
	* expr.c (expand_expr_real_2) <case VEC_PACK_FIX_TRUNC_EXPR,
	case VEC_PACK_TRUNC_EXPR>: Clear subtarget when changing mode.

(cherry picked from commit 008153c8435ca3bf587e11654c31f05c0f99b43a)

diff --git a/gcc/expr.c b/gcc/expr.c
index a0e194659659da378edc603b53d51128bfce9bd0..14a25c2545076aa61d99bdc6c0d22d07f9030e4e 100644 (file)
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -9809,6 +9809,7 @@ expand_expr_real_2 (sepops ops, rtx target, machine_mode tmode,
     case VEC_PACK_SAT_EXPR:
     case VEC_PACK_FIX_TRUNC_EXPR:
       mode = TYPE_MODE (TREE_TYPE (treeop0));
+      subtarget = NULL_RTX;
       goto binop;
 
     case VEC_PACK_TRUNC_EXPR:
@@ -9832,6 +9833,7 @@ expand_expr_real_2 (sepops ops, rtx target, machine_mode tmode,
          return eops[0].value;
        }
       mode = TYPE_MODE (TREE_TYPE (treeop0));
+      subtarget = NULL_RTX;
       goto binop;
 
     case VEC_PACK_FLOAT_EXPR: