[LLVMdev] Using sret AND thiscall calling convention

[Damien Gleizes]

Thank you for the answer.

I am not really sure, but I do not think I have the issue described here
http://llvm.org/bugs/show_bug.cgi?id=5058, because according to the attached
CC document, when using thiscall the caller is not responsible for stack
cleaning.

Seems to be a bug, I created a new entry here
http://llvm.org/bugs/show_bug.cgi?id=10645, I hope I done it correctly :)

Thanks again,
Damien


Eli Friedman-2 wrote:
> 
> On Fri, Aug 12, 2011 at 1:11 AM, Damien Gleizes <gleizesd at gmail.com>
> wrote:
>>
>> Hi all,
>>
>> I am trying to generate LLVM IR that calls an external C++ function
>> returning a structure by copy:
>> vec3 vec3::Cross(const vec3& iV) const;
>>
>> Here is the LLVM IR that I am generating for win32 ABI, which says that
>> the
>> first parameter should be a pointer to the return value:
>>
>> %vec3 = type <{ float, float, float }>
>>
>> define void @CPP_Return_Struct(%vec3* %v1, %vec3* %v2) inlinehint
>> alignstack(16) {
>> ENTRY:
>>  %"@0" = alloca %vec3, align 4
>>  call x86_thiscallcc void @vec3_Cross(%vec3* sret %"@0", %vec3* %v1,
>> %vec3*
>> %v2)
>>  ret void
>> }
>>
>> declare x86_thiscallcc void @vec3_Cross(%vec3* sret, %vec3*, %vec3*)
>> align 2
>>
>> It seems that the code generated by the JIT takes the first parameter for
>> the this value because of the X86_thiscall calling convention. However,
>> in
>> this particular case, the first parameter is the return value which is
>> tagged with the sret attribute.
>>
>> I have manually modified the X86GenCallingConv.inc to treat the second
>> parameter as this value when the first has been tagged with sret
>> attribute,
>> and it is working fine.
>>
>> But I am not sure if it is a (known?) bug or if I do not generate the
>> correct LLVM IR.
>>
>> I found nothing about this on the mailing list, I apologize if I missed
>> any
>> important information.
> 
> I would suggest avoiding any complicated calls from LLVM-generated
> code into Visual Studio-generated code.  For example,
> http://llvm.org/bugs/show_bug.cgi?id=5058 ,
> http://llvm.org/bugs/show_bug.cgi?id=5064 .  Not sure about the
> particular issue you're running into; looks like a bug at first
> glance.  The file that mostly controls this sort of thing is
> lib/Target/X86/X86CallingConv.td .
> 
> -Eli
> 
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> 
> 

-- 
View this message in context: http://old.nabble.com/Using-sret-AND-thiscall-calling-convention-tp32242156p32249435.html
Sent from the LLVM - Dev mailing list archive at Nabble.com.