r18252 - x*x -> sqr(x) optimization (Was: Re: [fpc-devel] ARM native compilation (Toshiba AC100))

[Jonas Maebe]

On 23 Sep 2011, at 01:21, Thomas Schatzl wrote:

> I found that 18251 is okay, but the newer ones are not when  
> compiling with -O2. It seems that one optimization that transforms  
> expressions of type x*x into sqr(x) for floats in 18252 (and 18257  
> and 18263 that seem to have been fixing issues with the original  
> implementation) causes troubles. With that in place, a compiler  
> cycle hangs at ppc2 compiling something (processing real2str.inc  
> from the system unit fyi).
>
> Florian, Jonas, any ideas? Seems to be related to softfloat code  
> generation because apparently other platforms are fine.

The optimization changes x*x into sqr(x). For ARM/softfloat, the  
compiler calls the fpc_sqr_real() helper from the RTL.

The code of this helper is:

     function fpc_sqr_real(d : ValReal) : ValReal;compilerproc;{$ifdef  
MATHINLINE}inline;{$endif}
     begin
       result := d*d;
     end;

So yes, this clearly puts the compiler into an endless loop. I'm not  
sure what would be a clean fix for this (other than completely  
disabling the transformation; does it improve the generated code that  
much beyond what CSE can achieve?)


Jonas