[gambit-list] Performance of different versions of gcc

Marc Feeley feeley at iro.umontreal.ca
Tue May 1 12:04:16 EDT 2012


On 2012-05-01, at 11:51 AM, Hendrik Boom wrote:

> On Tue, May 01, 2012 at 09:35:24AM -0400, Marc Feeley wrote:
>> 
>> 
>> Strangely, with clang 3.0 it takes less time to compile with -O2 
> than 
>> with -O1.
> 
> If I recall correctly, this phenomenon was first noticed in the 60's 
> with IBM's Fortran H compiler. It turns out that most of the time was 
> spent in the final process of putting instrutions together.  After 
> optimizing, there was less code to generate.

I doubt that this is the explanation here.  With -O1 it takes 2.4 times as long as -O1 to build Gambit, yet the resulting executable binary is the same size (actually the -O2 executable is 0.3% larger than the -O1 executable).

Marc



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