[LLVMdev] Using sret AND thiscall calling convention

[Damien Gleizes]

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.

Damien





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