[gcc r11-7775] cprop_hardreg: Ensure replacement reg has compatible mode [PR99221]

[Stefan Schulze Frielinghaus]

https://gcc.gnu.org/g:a28cc94a27529b3108ea85be9ef5557a3c95791d

commit r11-7775-ga28cc94a27529b3108ea85be9ef5557a3c95791d
Author: Stefan Schulze Frielinghaus <stefansf@linux.ibm.com>
Date:   Fri Mar 12 17:32:42 2021 +0100

    cprop_hardreg: Ensure replacement reg has compatible mode [PR99221]
    
    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.
    
    gcc/ChangeLog:
    
            * regcprop.c (find_oldest_value_reg): Ask target whether
              different mode is fine for replacement register.

Diff:
---
 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)