Re: [bug-gawk] speed regression when doing math with gawk 5

[Andrew J. Schorr]

On Sat, Apr 20, 2019 at 12:55:53AM +0000, Tom Gray wrote:
> I noticed a big speed regression in some of my programs when I upgraded from 
> 4.2.1 to 5.0
> 
> I traced the issue to commit c1f670b26, a fix for "Numeric assignment to $0"
> See discussion here: 
> http://lists.gnu.org/archive/html/bug-gawk/2018-07/msg00042.html
> 
> The speed hit shows up when you do a lot of numeric computation.
> The "fix" in commit c1f670b26 adds a call to force_string() (line 46, 
> interpret.h) which
> punishes every assignment with a number to string conversion.
> 
> In the examples here,
> gawk5 is built from the current master branch
> gawk5n has force_string() removed
> 
> $ time ~/src/gawk/gawk5 'BEGIN{ for(i=0; i<1e6; i++) y=sin(i) }'
> 
> real    0m3.980s
> user    0m3.962s
> sys     0m0.015s
> 
> 
> $ time ~/src/gawk/gawk5n 'BEGIN{ for(i=0; i<1e6; i++) y=sin(i) }'
> 
> real    0m0.130s
> user    0m0.124s
> sys     0m0.000s
> 
> 
> The original problem was the numeric assignment to $0 followed by the output 
> of $0.
> Numeric assignment does not automagically trigger generation of the string 
> representation
> required for output. A better way to do that is lazily like all other 
> conversions.
> The string is not needed until $0 gets sent to the output pipe.
> 
> Adding force_string() in do_print_rec() gets the job done.

Yikes. This is bad. But I don't think this fix quite works. With the patch
applied, I still have this problem in master:

bash-4.2$ yes a b c | sed 5q | ./gawk '{$0 = ++i; print $1}'                






As compared to an older version:

bash-4.2$ yes a b c | sed 5q | /bin/gawk '{$0 = ++i; print $1}'                
1
2
3
4
5

So this doesn't quite get the job done...

Regards,
Andy