[PATCH] cprop_hardreg: Ensure replacement reg has compatible mode [PR99221]

[Stefan Schulze Frielinghaus via Gcc-patches]

In addition to the existing check also ask the target whether a
replacement register may be accessed in a different mode than it was set
before.

Bootstrapped and regtested on IBM Z.  Ok for mainline?

gcc/ChangeLog:

        * regcprop.c (find_oldest_value_reg): Ask target whether
          different mode is fine for replacement register.
---
 gcc/regcprop.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/gcc/regcprop.c b/gcc/regcprop.c
index e1342f56bd1..02753a12510 100644
--- a/gcc/regcprop.c
+++ b/gcc/regcprop.c
@@ -474,7 +474,8 @@ find_oldest_value_reg (enum reg_class cl, rtx reg, struct 
value_data *vd)
        (set (...) (reg:DI r9))
      Replacing r9 with r11 is invalid.  */
   if (mode != vd->e[regno].mode
-      && REG_NREGS (reg) > hard_regno_nregs (regno, vd->e[regno].mode))
+      && (REG_NREGS (reg) > hard_regno_nregs (regno, vd->e[regno].mode)
+         || !REG_CAN_CHANGE_MODE_P (regno, mode, vd->e[regno].mode)))
     return NULL_RTX;
 
   for (i = vd->e[regno].oldest_regno; i != regno; i = vd->e[i].next_regno)
-- 
2.23.0