• bearophile (19/19) Mar 25 2014 If I compile this code with the latest ldc2 with -O -release
• David Nadlinger (7/8) Apr 04 2014 I don't think anything is likely to happen here on the LDC side, as it
• bearophile (4/10) Apr 04 2014 OK, thank you. So later I'll ask to the llvm devs :-)
• bearophile (9/11) Apr 11 2014 I was busy for few days, but now I have asked in the llvm

"bearophile" <bearophileHUGS lycos.com> writes:

If I compile this code with the latest ldc2 with -O -release 
-inline -noboundscheck, the inner loop is unrolled (while gdc 
unrolls it):


void main() {
     import core.stdc.stdio;

     enum uint n = 1 << 25;

     static immutable uint[5] factors = [101, 103, 107, 109, 113];
     uint c = 0;

     for (uint i = 1; i < n; i++)
         for (uint j = 0; j < 5; j++)
             if (i % factors[j] == 0) {
                 c++;
                 break;
             }

     printf("%u\n", c);
}


A little cheap unrolling could be present in -O.

Bye,
bearophile

"David Nadlinger" <code klickverbot.at> writes:

On 26 Mar 2014, at 0:25, bearophile wrote:
 A little cheap unrolling could be present in -O.

I don't think anything is likely to happen here on the LDC side, as it 
seems to be a question of tuning the LLVM optimizer.

I checked the generated IR and there aren't any obvious issues that 
would preclude optimization, and the passes selected by "opt" for the 
highest optimization level do not unroll the loop either.

David

"bearophile" <bearophileHUGS lycos.com> writes:

David Nadlinger:

 I don't think anything is likely to happen here on the LDC 
 side, as it seems to be a question of tuning the LLVM optimizer.

 I checked the generated IR and there aren't any obvious issues 
 that would preclude optimization, and the passes selected by 
 "opt" for the highest optimization level do not unroll the loop 
 either.

OK, thank you. So later I'll ask to the llvm devs :-)

Bye,
bearophile

"bearophile" <bearophileHUGS lycos.com> writes:

David Nadlinger:

 I don't think anything is likely to happen here on the LDC 
 side, as it seems to be a question of tuning the LLVM optimizer.

I was busy for few days, but now I have asked in the llvm 
channel, and the answer is that currently (unlike GDC) llvm 
doesn't unroll loops with multiple exits (it might break, it 
might not; so there are multiple possible exits).

They know about this limitation so perhaps there's not much point 
in opening a LLVM enhancement request.

Bye,
bearophile