[gcc r11-8594] expr: Fix up VEC_PACK_TRUNC_EXPR expansion [PR101046]

[Jakub Jelinek <jakub@gcc.gnu.org>]

https://gcc.gnu.org/g:5ece5ac99e804cccc3d8534d8871eb72e08edb06

commit r11-8594-g5ece5ac99e804cccc3d8534d8871eb72e08edb06
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Jun 15 11:36:47 2021 +0200

    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:
---
 gcc/expr.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/gcc/expr.c b/gcc/expr.c
index a0e19465965..14a25c25450 100644
--- 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: