[gambit-list] Possible new compilation strategy for read-char and write-char

Bradley Lucier lucier at math.purdue.edu
Sun Feb 11 12:18:44 EST 2007


macro-read-char is a fair amount of code to inline at each site of  
read-char.  We have with the original

-rw-r--r--  1 lucier pfaculty  107585 Feb 10 12:47 bewig2.c
-rwxr-xr-x  1 lucier pfaculty   52001 Feb 10 12:47 bewig2.o1*
-rw-r--r--  1 lucier pfaculty   10799 Feb 10 11:36 bewig2.scm

If we replace all 16 instances of read-char with macro-read-char, we get

-rw-r--r--  1 lucier pfaculty  175125 Feb 10 13:38 bewig2+macro-read- 
-rwxr-xr-x  1 lucier pfaculty   71575 Feb 10 13:38 bewig2+macro-read- 
-rw-r--r--  1 lucier pfaculty   10925 Feb 10 13:38 bewig2+macro-read- 

Part of the problem here is that, if function A calls function B,  
Gambit's inlining heuristic looks at the size of the macro-expanded  
function A before deciding whether to inline function B into A; if  
macro-expansion increases the size of A a lot (say, by expanding  
macro-read-char ;-), then B is more likely to be inlined into A.   
This happened with two of the state-machine functions in read-csv- 

If, instead, we add a simple function my-read-char

(define (my-read-char port)
   (macro-read-char port))

and then replace calls to read-char by calls to my-read-char, we get

-rw-r--r--  1 lucier pfaculty  134833 Feb 11 11:50 bewig3.c
-rwxr-xr-x  1 lucier pfaculty   59349 Feb 11 11:50 bewig3.o1*
-rw-r--r--  1 lucier pfaculty   10929 Feb 11 11:50 bewig3.scm

and the times are almost as good as when macro-read-char is inlined  
at all call sites of read-char, 113ms on Philip's benchmark instead  
of 111ms.  Recall that the time for using read-char is 435ms, so  
we're about four times as fast.

So perhaps you should add another compilation strategy---for files  
that have calls to read-char (or to any functions that are big  
enough, or have a big enough fast path, that you don't want to inline  
them into each call site), put in a local function that has the code  
for macro-read-char, and redirect calls to read-char to this local  
function (under suitable circumstances, of course).


More information about the Gambit-list mailing list