Fix UBSAN error, shifting 64 bit value by 64.

2020-03-13  Aaron Sawdey  <acsawdey@linux.ibm.com>

	PR target/92379
	* config/rs6000/rs6000.c (num_insns_constant_multi) Don't shift a
	64-bit value by 64 bits (UB).

gcc/ChangeLog

+2020-03-13  Aaron Sawdey  <acsawdey@linux.ibm.com>
+
+	PR target/92379
+	* config/rs6000/rs6000.c (num_insns_constant_multi) Don't shift a
+	64-bit value by 64 bits (UB).
+
 2020-03-13  Vladimir Makarov  <vmakarov@redhat.com>
 
 	PR rtl-optimization/92303

gcc/config/rs6000/rs6000.c

@@ -5612,7 +5612,10 @@ num_insns_constant_multi (HOST_WIDE_INT value, machine_mode mode)
 	  && rs6000_is_valid_and_mask (GEN_INT (low), DImode))
 	insns = 2;
       total += insns;
-      value >>= BITS_PER_WORD;
+      /* If BITS_PER_WORD is the number of bits in HOST_WIDE_INT, doing
+	 it all at once would be UB. */
+      value >>= (BITS_PER_WORD - 1);
+      value >>= 1;
     }
   return total;
 }