[LLVMdev] Passing structures as pointers, MSVC x64 style

[Carl Norum]

On Feb 21, 2011, at 4:51 PM, NAKAMURA Takumi wrote:

> Carl,
> 
> See clang/lib/CodeGen/TargetInfo.cpp.
> 
>    // FIXME: mingw64-gcc emits 128-bit struct as i128
>    if (Size <= 128 &&
>        (Size & (Size - 1)) == 0)
>      return ABIArgInfo::getDirect(llvm::IntegerType::get(getVMContext(),
>                                                          Size));
> 
> It was my workaround, sorry.
> Please check to tweak the clause (128 to 64) and lemme know.

Hi Takumi,

I think you hit the nail on the head with that one.  Changing that constant to 64 seems to have done the trick.  Here's the new disassembled output:

    _byValue:
    0000000000000000	pushq	%rbp
    0000000000000001	movq	%rsp,%rbp
    0000000000000004	subq	$0x30,%rsp
    0000000000000008	leaq	0xf0(%rbp),%rdx
    000000000000000c	movq	0x00000008(%rip),%rax
    0000000000000013	movq	%rax,0xf8(%rbp)
    0000000000000017	movq	0x00000000(%rip),%rax
    000000000000001e	movq	%rax,0xf0(%rbp)
    0000000000000022	movl	$0x00000001,%ecx
    0000000000000027	callq	0x0000002c
    000000000000002c	addq	$0x30,%rsp
    0000000000000030	popq	%rbp
    0000000000000031	ret

%rdx is now getting the address of a copy of the struct!  Patch attached; if it looks good to you I'll commit it.

-- Carl

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