trying to get a registerised alpha build

[Simon Marlow]

Duncan Coutts wrote:
> On Fri, 2006-03-31 at 11:43 +0100, Simon Marlow wrote:
> 
>>Duncan Coutts wrote:
>>
>>
>>>What would you recommend is the bat way for us to verify that each bit
>>>of the registerised build is working? If we turn everything on including
>>>the mangler and it breaks where do we start debugging?
>>
>>I usually do this in one big step.
> 
> 
> Right 'o. :-)
> 
> 
>>Regarding debugging, I just wrote this wiki page:
>>
>>   http://hackage.haskell.org/trac/ghc/wiki/DebuggingGhcCrashes
>>
>>That should tell you everything you need to know, please feel free to 
>>expand it as you discover things.
> 
> 
> That's fantastic, thanks.
> 
> 
>>>Is it possible to build without tailcalls (ie using the
>>>mini-interpreter) but using the stg->machine register mappings?
>>
>>Certainly.  I think if you use -optc-DUSE_MINIINTERPRETER and 
>>-fno-asm-mangling everywhere, that should get you registers but no 
>>mangling or tail calls.
> 
> 
> Unfortunately this doesn't quite work because the TABLES_NEXT_TO_CODE
> ends up inconsistent. I'm not quite sure why that happens to be honest.
> 
> Our clue is that the sanity check in initStorage barfs:
>   ASSERT(LOOKS_LIKE_CLOSURE_PTR(&stg_dummy_ret_closure));
> 
> By looking at this in gdb (thanks again for the ghc gdb guide!) we found
> that this is because this closure was generated assuming
> TABLES_NEXT_TO_CODE to be true but of course since we're using
> -optc-DUSE_MINIINTERPRETER then the rts .c code is getting compiled
> with !TABLES_NEXT_TO_CODE which changes the definition of
> LOOKS_LIKE_CLOSURE_PTR.

I think the culprit is this bit of code in ghc/codeGen/SMRep.lhs:

tablesNextToCode :: Bool
#if defined(ia64_TARGET_ARCH) || defined(powerpc64_TARGET_ARCH)
tablesNextToCode = False
#else
tablesNextToCode = not opt_Unregisterised
#endif

This is the compiler's idea of TABLES_NEXT_TO_CODE, which doesn't match 
the RTS's idea from RtsConfig.h.  I suggest you just tweak this directly 
- the right way is probably to have another build system variable eg. 
$(GhcTablesNextToCode), but that's tricky to get right, and not 
generally useful (but by all means go ahead if you want).

Also, I'm worried about the generation of 
ghc/includes/DerivedConstants.h, because this code in 
ghc/includes/Makefile says this:

ifeq "$(GhcUnregisterised)" "YES"
SRC_CC_OPTS += -DNO_REGS -DUSE_MINIINTERPRETER
endif

So if you want USE_MINIINTERPRETER without GhcUnregisterised, it better 
be in SRC_CC_OPTS here.

Cheers,
	Simon