Robert Klemme
3/28/2008 4:24:00 PM
On 28.03.2008 15:38, Heesob Park wrote:
> I do not undertand why ruby doesn't do any optimization at all during
> parsing time.
Because, as others have pointed out already, at parse time it is not
known what the code will do.
> Some optimization maybe affects debugging process.
> Nevertheless, it seems "Constant folding" is not harmful but helpful.
> I tried some pre-evaluation of constant or literal nodes in parsing
> time.
>
> Consider this code
>
> i = 320 * 200 * 32
>
> Original ruby-1.8.6 parsed it like this:
>
> 0:[NODE_BLOCK],0xb7f93ce4,p1:-9,p2:12,p3:1}
> -9:[NODE_NEWLINE],0xb7f93d98,u1:0,u2:1,p3:-17}
> -17:[NODE_LASGN],0xb7f93e38,u1:10473,p2:-10,u3:2}
> -10:[NODE_CALL],0xb7f93dac,p1:-13,u2:42,p3:-11}
> -13:[NODE_CALL],0xb7f93de8,p1:-16,u2:42,p3:-14}
> -16:[NODE_LIT],0xb7f93e24,u1:641,u2:0,u3:0}
> -14:[NODE_ARRAY],0xb7f93dfc,p1:-15,u2:1,u3:0}
> -15:[NODE_LIT],0xb7f93e10,u1:401,u2:0,u3:0}
> -11:[NODE_ARRAY],0xb7f93dc0,p1:-12,u2:1,u3:0}
> -12:[NODE_LIT],0xb7f93dd4,u1:65,u2:0,u3:0}
>
> My modified ruby parsed it like this:
>
> 0:[NODE_BLOCK],0xb7f5cd0c,p1:-9,p2:12,p3:1}
> -9:[NODE_NEWLINE],0xb7f5cdc0,u1:0,u2:1,p3:-15}
> -15:[NODE_LASGN],0xb7f5ce38,u1:10473,p2:-10,u3:2}
> -10:[NODE_LIT],0xb7f5cdd4,u1:4096001,u2:0,u3:0}
$ ruby -e 'class Fixnum; def *(o) 666 end;end; puts 320 * 200 * 32'
666
Ooops!
Without fiddling:
robert@fussel ~
$ ruby -e 'puts 1/2'
0
robert@fussel ~
$ ruby -r mathn -e 'puts 1/2'
1/2
> A little more complex code
>
> c = (12-3) * Math.sin(100) + 1.300 * (2 + 3) * Math.log(100)
>
> Original parser:
> 0:[NODE_BLOCK],0xb7f35b08,p1:-9,p2:1,p3:1}
> -9:[NODE_NEWLINE],0xb7f35bbc,u1:0,u2:4,p3:-38}
> -38:[NODE_LASGN],0xb7f35e00,u1:10473,p2:-10,u3:2}
> -10:[NODE_CALL],0xb7f35bd0,p1:-27,u2:43,p3:-11}
> -27:[NODE_CALL],0xb7f35d24,p1:-33,u2:42,p3:-28}
> -33:[NODE_NEWLINE],0xb7f35d9c,u1:0,u2:4,p3:-34}
> -34:[NODE_CALL],0xb7f35db0,p1:-37,u2:45,p3:-35}
> -37:[NODE_LIT],0xb7f35dec,u1:25,u2:0,u3:0}
> -35:[NODE_ARRAY],0xb7f35dc4,p1:-36,u2:1,u3:0}
> -36:[NODE_LIT],0xb7f35dd8,u1:7,u2:0,u3:0}
> -28:[NODE_ARRAY],0xb7f35d38,p1:-29,u2:1,u3:0}
> -29:[NODE_CALL],0xb7f35d4c,p1:-32,u2:9961,p3:-30}
> -32:[NODE_CONST],0xb7f35d88,u1:9925,u2:0,u3:0}
> -30:[NODE_ARRAY],0xb7f35d60,p1:-31,u2:1,u3:0}
> -31:[NODE_LIT],0xb7f35d74,u1:201,u2:0,u3:0}
> -11:[NODE_ARRAY],0xb7f35be4,p1:-12,u2:1,u3:0}
> -12:[NODE_CALL],0xb7f35bf8,p1:-18,u2:42,p3:-13}
> -18:[NODE_CALL],0xb7f35c70,p1:-25,u2:42,p3:-19}
> -25:[NODE_LIT],0xb7f35cfc,p1:-26,u2:0,u3:0}
> -19:[NODE_ARRAY],0xb7f35c84,p1:-20,u2:1,u3:0}
> -20:[NODE_NEWLINE],0xb7f35c98,u1:0,u2:4,p3:-21}
> -21:[NODE_CALL],0xb7f35cac,p1:-24,u2:43,p3:-22}
> -24:[NODE_LIT],0xb7f35ce8,u1:5,u2:0,u3:0}
> -22:[NODE_ARRAY],0xb7f35cc0,p1:-23,u2:1,u3:0}
> -23:[NODE_LIT],0xb7f35cd4,u1:7,u2:0,u3:0}
> -13:[NODE_ARRAY],0xb7f35c0c,p1:-14,u2:1,u3:0}
> -14:[NODE_CALL],0xb7f35c20,p1:-17,u2:10057,p3:-15}
> -17:[NODE_CONST],0xb7f35c5c,u1:9925,u2:0,u3:0}
> -15:[NODE_ARRAY],0xb7f35c34,p1:-16,u2:1,u3:0}
> -16:[NODE_LIT],0xb7f35c48,u1:201,u2:0,u3:0}
> Modified parser:
> 0:[NODE_BLOCK],0xb7f0fae8,p1:-9,p2:1,p3:1}
> -9:[NODE_NEWLINE],0xb7f0fb9c,u1:0,u2:4,p3:-40}
> -40:[NODE_LASGN],0xb7f0fe08,u1:10473,p2:-10,u3:2}
> -10:[NODE_LIT],0xb7f0fbb0,p1:-11,u2:0,u3:0}
Same story as above.
> String operation code
> s = ("hello " + "world ")*100
Note that in the code above the only constant is "100". The sequence
"hello" is a String constructor - not a constant - as you can easily see:
irb(main):012:0> (1..5).map { "hello".object_id }
=> [1073415980, 1073415960, 1073415940, 1073415920, 1073415900]
irb(main):013:0> (1..5).map { "hello".object_id }.uniq
=> [1073407290, 1073407270, 1073407250, 1073407230, 1073407210]
> Original parser:
> 0:[NODE_BLOCK],0xb7fa4c74,p1:-11,p2:1,p3:1}
> -11:[NODE_NEWLINE],0xb7fa4d50,u1:0,u2:2,p3:-22}
> -22:[NODE_LASGN],0xb7fa4e2c,u1:10473,p2:-12,u3:2}
> -12:[NODE_CALL],0xb7fa4d64,p1:-15,u2:42,p3:-13}
> -15:[NODE_NEWLINE],0xb7fa4da0,u1:0,u2:2,p3:-16}
> -16:[NODE_CALL],0xb7fa4db4,p1:-19,u2:43,p3:-21}
> -19:[NODE_STR],0xb7fa4df0,p1:-20,u2:0,u3:0}
> -21:[NODE_ARRAY],0xb7fa4e18,p1:-17,u2:1,u3:0}
> -17:[NODE_STR],0xb7fa4dc8,p1:-18,u2:0,u3:0}
> -13:[NODE_ARRAY],0xb7fa4d78,p1:-14,u2:1,u3:0}
> -14:[NODE_LIT],0xb7fa4d8c,u1:2001,u2:0,u3:0}
>
> Modified parser:
> 0:[NODE_BLOCK],0xb7efdc6c,p1:-11,p2:1,p3:1}
> -11:[NODE_NEWLINE],0xb7efdd48,u1:0,u2:2,p3:-22}
> -22:[NODE_LASGN],0xb7efde24,u1:10473,p2:-12,u3:2}
> -12:[NODE_STR],0xb7efdd5c,p1:-13,u2:0,u3:0}
>
> In the loop it make considerable difference
> With the code
> for i in 1..10000
> s = "hello"*10000
> end
> puts s
>
> Original ruby:
> real 0m2.591s
> user 0m2.579s
> sys 0m0.013s
>
> Modified ruby:
> real 0m0.010s
> user 0m0.007s
> sys 0m0.003s
>
> What do you think of the minimum optimization?
I think: if it was that easy, Matz would have done it already. But it
ain't that easy and if you want to have constant expressions simply
assign them to a constant and use that value.
I = 320 * 200 * 32
Kind regards
robert