[fpc-devel] register allocator seems to be using S20 for two things at the same time (related to armhf porting work)

peter green plugwash at p10link.net
Sun Mar 18 13:41:56 CET 2012

Daniƫl Mantione wrote:
> Please use the command line option -sr to check the generated code 
> before register allocation. 
Done and attatched.
> You can likely find the cause in there.
The code with imaginary registers looks correct to me. It seems to load 
each parameter into a seperate even numbered imaginary register (using 
odd numbered imaginary registers as temporaries in the process) 
allocating them as it goes. Then copies them to the locations needed for 
the function call deallocating them as it goes.

So it seems to me that the problem is in the translation of the form 
using imaginary registers to the form using real registers. Can you 
explain (or point me to documentation on) how this form is translated 
into a form using real registers. In particular what exactly happens 
when there are not enough real registers free to assign a real register 
for every imaginary register that is in use at a given time?

My current suspiscion is that something is missing regarding handling of 
running out of VFP registers and it hasn't been noticed before because 
noone has tried to do what i'm doing (implementing a calling convention 
using VFP registers and then stress testing it) but i've no idea where 
to look in the sourcecode to confirm/refute that idea.
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