[LLVMdev] [PATCH] New calling convention for use by GHC

[David Terei]

OK, new patch attached. Hopefully in time for 2.7.

Chris Lattner wrote:
> 1) is the GHC calling conv intended to be target specific?  If it is x86 specific, it should get an X86 prefix.  If not, it should move up to be #10 after Cold.

No its intended to be supported on any platforms that GHC is supported
on, which is just x86 and SPARC at the moment. At the moment I've just
done X86, will try to work on getting it implemented on SPARC next.

> 2) In either case, please document the new calling convention in docs/LangRef.html#callingconv

Done.

> 3) IN X86RegisterInfo.cpp, this patch:
>
>     if (Is64Bit) {
>       if (IsWin64)
> -      return CalleeSavedRegsWin64;
> +      return (ghcCall ? GhcCalleeSavedRegsWin64 : CalleeSavedRegsWin64);
>       else
> -      return (callsEHReturn ? CalleeSavedRegs64EHRet : CalleeSavedRegs64Bit);
> +      if (ghcCall)
> +        return (callsEHReturn ?
> +                  GhcCalleeSavedRegs64EHRet : GhcCalleeSavedRegs64Bit);
> +      else
> +        return (callsEHReturn ? CalleeSavedRegs64EHRet : CalleeSavedRegs64Bit);
>
> Seems like it could be simplified.  Have you tested the Win64 support?
 > It isn't clear why your patch needs to depend on the host ABI here.
 > Also, does EHRet matter for your calling conv?

This is true. The GHC call convention is only ever used as a tail call
by GHC, so really all of this could be changed so that it just returns
no callee saves regardless of ABI. Also, I assume EH = Exception
Handling? If so, no EHRet doesn't matter. The new patch takes this
approach.

>
>
> 4) In X86ISelLowering.cpp:
>
> -    if (!Is64Bit&&  CallConv != CallingConv::Fast&&  ArgsAreStructReturn(Ins))
> +    if (!Is64Bit&&  CallConv != CallingConv::Fast&&
> +          CallConv != CallingConv::GHC&&  ArgsAreStructReturn(Ins))
>
> This should probably use !IsTailCallConvention(CallConv) instead of duplicating the two conventions
>
>     assert(!(isVarArg&&  CallConv == CallingConv::Fast)&&
>            "Var args not supported with calling convention fastcc");
> +  assert(!(isVarArg&&  CallConv == CallingConv::GHC)&&
> +         "Var args not supported with calling convention ghc");
>
> Likewise.
>
> @@ -2151,7 +2168,8 @@
>     unsigned NumBytesForCalleeToPush;
>     if (IsCalleePop(isVarArg, CallConv))
>       NumBytesForCalleeToPush = NumBytes;    // Callee pops everything
> -  else if (!Is64Bit&&  CallConv != CallingConv::Fast&&  IsStructRet)
> +  else if (!Is64Bit&&  CallConv != CallingConv::Fast&&
> +             CallConv != CallingConv::GHC&&  IsStructRet)
>
> Likewise.

Done.

>
> 5) Please include a .ll testcase that uses the new calling conv and shows that the arguments are getting passed right.  For example it could take two ints add them together and return it, the generated code should show the assigned registers.
>

Done.

> Otherwise the patch looks great, please resend a new spin of it and I'll commit it.  Thanks! Also, congrats on the great work on LLVM+GHC,

Thanks.

~ David
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