fib, new primitives, and useless analysis

[Stephen Weeks]

> In general, though, I think that optimization needs some tweaking.  It's
> coming about because there is an implicit assumption that Prim's do not
> side-effect. (true?)

False.  The optimization is only done for prims p such that
Prim.isFunctional p.

 We can continue the debate about whether or not Int.+
> should or should not raise Overflow, but certainly FFI's should be
> considered side-effecting.

Of course.  Here is the definition of Prim.Name.maySideEffect

      val maySideEffect =
	 fn Array_update => true
	  | Exn_setTopLevelHandler => true
	  | FFI _ => true
	  | GC_collect => true
	  | MLton_halt => true
	  | Ref_assign => true
	  | Thread_copy => true
	  | Thread_copyShrink => true
	  | Thread_finishHandler => true
	  | Thread_switchTo => true
	  | Word8Array_updateWord => true
	  | World_save => true
	  | _ => false

And here is the definition of Prim.Name.isFunctional

      val isFunctional =
	 fn Array_length => true
	  | Byte_byteToChar => true
	  | Byte_charToByte => true
	  | Char_lt => true
	  | Char_le => true
	  | Char_gt => true
	  | Char_ge => true
	  | Char_chr => true
	  | Char_ord => true
	  | Constant _ => true
	  | Cpointer_isNull => true
	  | Exn_name => true
	  | Int_mul => true
	  | Int_add => true
	  | Int_sub => true
	  | Int_lt => true
	  | Int_le => true
	  | Int_gt => true
	  | Int_ge => true
	  | Int_geu => true
	  | Int_gtu => true
	  | Int_quot => true
	  | Int_rem => true
	  | Int_neg => true
	  | IntInf_add => true
	  | IntInf_areSmall => true
	  | IntInf_fromWord => true
	  | IntInf_isSmall => true
	  | IntInf_mul => true
	  | IntInf_neg => true
	  | IntInf_quot => true
	  | IntInf_rem => true
	  | IntInf_sub => true
	  | IntInf_toString => true
	  | IntInf_toWord => true
	  | MLton_eq => true
	  (* MLton_equal is commented out because I don't want globalization or
	   * constant propagation to move it into the globals, because
	   * polymorphic equality isn't implemented there.
	   *)
(*	  | MLton_equal => true *)
	  | MLton_id => true
	  | Real_nequal => true
	  | Real_mul => true
	  | Real_muladd => true
	  | Real_mulsub => true
	  | Real_add => true
	  | Real_sub => true
	  | Real_div => true
	  | Real_lt => true
	  | Real_le => true
	  | Real_equal => true
	  | Real_gt => true
	  | Real_ge => true
	  | Real_qequal => true
	  | Real_abs => true
	  | Real_fromInt => true
	  | Real_toInt => true
	  | Real_neg => true
	  | Vector_sub => true
	  | Vector_length => true
	  | Word8_mul => true
	  | Word8_add => true
	  | Word8_sub => true
	  | Word8_lt => true
	  | Word8_lshift => true
	  | Word8_le => true
	  | Word8_gt => true
	  | Word8_ge => true
	  | Word8_rshift => true
	  | Word8_andb => true
	  | Word8_div => true
	  | Word8_fromInt => true
	  | Word8_fromLargeWord => true
	  | Word8_mod => true
	  | Word8_notb => true
	  | Word8_orb => true
	  | Word8_toInt => true
	  | Word8_toIntX => true
	  | Word8_toLargeWord => true
	  | Word8_toLargeWordX => true
	  | Word8_xorb => true
	  | Word8_arshift => true
	  | Word32_mul => true
	  | Word32_add => true
	  | Word32_sub => true
	  | Word32_lt => true
	  | Word32_lshift => true
	  | Word32_le => true
	  | Word32_gt => true
	  | Word32_ge => true
	  | Word32_rshift => true
	  | Word32_andb => true
	  | Word32_div => true
	  | Word32_fromInt => true
	  | Word32_mod => true
	  | Word32_notb => true
	  | Word32_orb => true
	  | Word32_toIntX => true
	  | Word32_xorb => true
	  | Word32_arshift => true
	  | _ => false