v3_kernel: Generate optimized code for guards

The compiler produces poor code for complex guard expressions with andalso/orelse.
Here is an example from the filename module:

-define(IS_DRIVELETTER(Letter),(((Letter >= $A) andalso (Letter =< $Z)) orelse
				((Letter >= $a) andalso (Letter =< $z)))).
skip_prefix(Name, false) ->
    Name;
skip_prefix([L, DrvSep|Name], DrvSep) when ?IS_DRIVELETTER(L) ->
    Name;
skip_prefix(Name, _) ->
    Name.

beam_bool fails to simplify the code for the guard, leaving several 'bif'
instructions:

{function, skip_prefix, 2, 49}.
  {label,48}.
    {line,[{location,"filename.erl",187}]}.
    {func_info,{atom,filename},{atom,skip_prefix},2}.
  {label,49}.
    {test,is_ne_exact,{f,52},[{x,1},{atom,false}]}.
    {test,is_nonempty_list,{f,52},[{x,0}]}.
    {get_list,{x,0},{x,2},{x,3}}.
    {test,is_nonempty_list,{f,52},[{x,3}]}.
    {get_list,{x,3},{x,4},{x,5}}.
    {bif,'=:=',{f,52},[{x,1},{x,4}],{x,6}}.
    {test,is_ge,{f,50},[{x,2},{integer,65}]}.
    {bif,'=<',{f,52},[{x,2},{integer,90}],{x,7}}.
    {test,is_eq_exact,{f,51},[{x,7},{atom,false}]}.
    {test,is_ge,{f,50},[{x,2},{integer,97}]}.
    {bif,'=<',{f,52},[{x,2},{integer,122}],{x,7}}.
    {jump,{f,51}}.
  {label,50}.
    {move,{atom,false},{x,7}}.
  {label,51}.
    {bif,'=:=',{f,52},[{x,7},{atom,true}],{x,7}}.
    {test,is_eq_exact,{f,52},[{x,6},{atom,true}]}.
    {test,is_eq_exact,{f,52},[{x,7},{atom,true}]}.
    {move,{x,5},{x,0}}.
    return.
  {label,52}.
    return.

We can add optimizations of guard tests to v3_kernel to achive a better result:

{function, skip_prefix, 2, 49}.
  {label,48}.
    {line,[{location,"filename.erl",187}]}.
    {func_info,{atom,filename},{atom,skip_prefix},2}.
  {label,49}.
    {test,is_ne_exact,{f,51},[{x,1},{atom,false}]}.
    {test,is_nonempty_list,{f,51},[{x,0}]}.
    {get_list,{x,0},{x,2},{x,3}}.
    {test,is_nonempty_list,{f,51},[{x,3}]}.
    {get_list,{x,3},{x,4},{x,5}}.
    {test,is_eq_exact,{f,51},[{x,1},{x,4}]}.
    {test,is_ge,{f,51},[{x,2},{integer,65}]}.
    {test,is_lt,{f,50},[{integer,90},{x,2}]}.
    {test,is_ge,{f,51},[{x,2},{integer,97}]}.
    {test,is_ge,{f,51},[{integer,122},{x,2}]}.
  {label,50}.
    {move,{x,5},{x,0}}.
    return.
  {label,51}.
    return.

Looking at the STDLIB application, there were 112 lines of BIF calls in guards
that beam_bool failed to convert to test instructions. This commit eliminates
all those BIF calls.

Here is how I counted the instructions:

$ PATH=$ERL_TOP/bin:$PATH erlc -I ../include -I ../../kernel/include -S *.erl
$ grep "bif,'[=<>]" *.S | grep -v f,0
dets.S:    {bif,'=:=',{f,547},[{x,4},{atom,read_write}],{x,4}}.
dets.S:    {bif,'=:=',{f,547},[{x,5},{atom,saved}],{x,5}}.
dets.S:    {bif,'=:=',{f,589},[{x,5},{atom,read}],{x,5}}.
.
.
.
$ grep "bif,'[=<>]" *.S | grep -v f,0 | wc
     112     224    6765
$

0 files changed, 0 insertions, 0 deletions