Re: [Haskell-cafe] Re: Difference in Runtime but no explanation

On Tue, 2009-12-15 at 10:56 -0800, Thomas DuBuisson wrote:

On Tue, Dec 15, 2009 at 10:30 AM, Maciej Piechotka wrote:

...

My results (ghc 6.12.1, Core 2 Duo 2.8 GHz, Linux 2.6.32, Gentoo):

Not Optimized & not compiled: First: 12.47 secs, 1530911440 bytes Second: 17.40 secs, 1929614816 bytes Optimized & compiled: First: 1.24 secs, 966280832 bytes Second: 1.11 secs, 966277152 bytes

Seconded, I consistently get 0.350 seconds vs 0.300 when compiling the original code via -O2.

...

Repeating gave similar results - first being better w/out optimalization as 1.2:1.7 and second being better with optimalizations (-O).

Why the first one is better unoptimalized?

I think thats not a specific enough question. I replaced the 'Integer' with 'Int' and found (via -ddump-asm) that the assembly is _identical_. A test shows what you would expect - the performance was identical. So the question in my mind is what presumably trivial optimization doesn't happen when Integer is used?

Thomas

Ups. I forgot about types :( Integer Not optimized & compiled: First: 19.81 secs, 2774731128 bytes Second: 22.64 secs, 3092270464 bytes Optimized & compiled: First: 0.64 secs, 980673088 bytes Second: 0.65 secs, 975408024 bytes Int Not optimized & compiled: First: 19.60 secs, 2774208376 bytes Second: 22.65 secs, 3092274608 bytes Optimized & compiled: First: 0.46 secs, 808978336 bytes Second: 0.43 secs, 803460216 bytes As for Integer. In case of Int l+1 `seq` something it can be simply transformed into (pseudo-assembler): call l incq %rax ; Or addq $1, %rax call something But for Integer: call l movq $1, %rbx call Integer.+ call something Regards