[Tinycc-devel] Struct and float parameter passing ir arm-gen.c

[Thomas Preud'homme]

Greatings everyone,

I've been reading arm-gen.c lately and was a bit surprised by some code 
related to struct and float (including double and long double) parameter 
passing in gfunc_call. It's probably just a mistake from my reading in which 
case I'd appreciate you explained me the bits I missed.

 As I understand it [0], the array /plan/ is used to memorize the association 
between parameters and the register(s) in which they are passed. The 
association is done via a line plan[nb_args-1-i][1]=args_size/4; in a switch 
case done in the second for loop browsing the parameter.

[0] From lines like:
  s=regmask(plan[nb_args-i-1][1]; and:
  todo&=~(1<<plan[nb_args-i-1][1]) with TODO being used to generate ldm 
instruction later.

What bothers me is that the association is only done in the general case (type 
!= float, double, long double and struct) but args_size is increased in general 
case *and* struct + floats case. This mean that if the first parameter of a 
function is a structure of size 8 bytes, then core registers r0 and r1 are 
skipped although they could be used by following integer parameter.

It's also in opposition to what require stage C in chapter 5.5 of AAPCS 
documentation. Basically it says either a type qualify for co-processor 
register in which case it's passed in co-processor register or on stack but 
without touching NCRN (Next Core Register Number). Or it does not qualify for 
co-processor register (for example if there is no co-processor like when tcc 
produce code compatible with system without VFP, ie TCC_ARM_VFP is undefined) 
and is allocated one or several core register (and can be half on registers 
and half on stack).

I hope I was clear enough. So, did I miss something (probably obvious) or 
there is a bug in there?

Best regards,

Thomas

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