[PATCH] PR rtl-optimization/100263: Ensure register can change mode

[Stefan Schulze Frielinghaus via Gcc-patches]

For move2add_valid_value_p we also have to ask the target whether a
register can be accessed in a different mode than it was set before.

gcc/ChangeLog:

        PR rtl-optimization/100263
        * postreload.c (move2add_valid_value_p): Ensure register can
        change mode.

Bootstrapped and regtested releases/gcc-{8,9,10,11} and master on IBM Z.
Ok for those branches?

---
 gcc/postreload.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/gcc/postreload.c b/gcc/postreload.c
index dc67643384d..60a622dbaf3 100644
--- a/gcc/postreload.c
+++ b/gcc/postreload.c
@@ -1725,7 +1725,8 @@ move2add_valid_value_p (int regno, scalar_int_mode mode)
     {
       scalar_int_mode old_mode;
       if (!is_a <scalar_int_mode> (reg_mode[regno], &old_mode)
-         || !MODES_OK_FOR_MOVE2ADD (mode, old_mode))
+         || !MODES_OK_FOR_MOVE2ADD (mode, old_mode)
+         || !REG_CAN_CHANGE_MODE_P (regno, old_mode, mode))
        return false;
       /* The value loaded into regno in reg_mode[regno] is also valid in
         mode after truncation only if (REG:mode regno) is the lowpart of
-- 
2.23.0