ubsan: tc-z80.c:3656 shift exponent 32 is too large

[Alan Modra]

	* config/tc-z80.c (is_overflow): Avoid too large shift.

diff --git a/gas/config/tc-z80.c b/gas/config/tc-z80.c
index 45fcd6fbf7..2e17d00552 100644
--- a/gas/config/tc-z80.c
+++ b/gas/config/tc-z80.c
@@ -3653,7 +3653,7 @@ md_assemble (char *str)
 static int
 is_overflow (long value, unsigned bitsize)
 {
-  long fieldmask = (1UL << bitsize) - 1;
+  long fieldmask = (2UL << (bitsize - 1)) - 1;
   long signmask = ~fieldmask;
   long a = value & fieldmask;
   long ss = a & signmask;
-- 
Alan Modra
Australia Development Lab, IBM