[LLVMdev] C struct as function argument

[Eli Friedman]

On Mon, Jun 20, 2011 at 11:33 AM, Michael Tindal <babyplatypus at me.com> wrote:
> I've been working on a wrapper for LLVM's C++ API to use from Objective-C for a scripting language I'm working on.  I currently have an issue with passing arguments to a function that takes a struct argument.
>
> typedef struct _test_struct {
>    int x;
>    int y;
> } test_struct;
>
> id testLLVMStructFuncCall(test_struct x) {
>    NSLog(@"%d %d",x.x,x.y);
>    return N(x.x + x.y);
> }
>
> -(void) testLLVMStructFuncCall {
>    CGKModule* myMod = [CGKModule moduleWithName:@"llvm_structfunccall_test"];
>    CGKType* testStructType = [CGKType structTypeWithElementTypes:[NSArray arrayWithObjects:[CGKType intTypeWith32Bits],[CGKType intTypeWith32Bits],nil]];
>    CGKFunction* lfunc = [CGKFunction functionWithName:@"testLLVMStructFuncCall" types:[NSArray arrayWithObjects:[CGKType idType],testStructType,nil] intoModule:myMod];
>    CGKFunction* rfunc = [CGKBuilder createStandaloneCallForFunction:lfunc withArguments:[NSArray
>                                                                                          arrayWithObjects:
>                                                                                          [CGKConstant getStructOfType:testStructType
>                                                                                                            withValues:[NSArray arrayWithObjects:[CGKConstant getIntConstant:N(10) bits:32],
>                                                                                                                        [CGKConstant getIntConstant:N(25) bits:32],nil]],nil]
>                                                            inModule:myMod];
>    [myMod dump];
>    id var = [[CGKRunner runnerForModule:myMod] runCGKFunction:rfunc];
>    assertThat(var,is(equalTo(N(35))));
> }
>
> Thats the code in question.  The CGK* types are part of my wrapper, and simply wrap the necessary part of the LLVM API.
>
> Test Case '-[SVFunctionTests testLLVMStructFuncCall]' started.
> ; ModuleID = 'llvm_structfunccall_test'
>
> %0 = type { i32, i32 }
>
> declare i64* @testLLVMStructFuncCall(%0)
>
> define i64* @0() {
> entry:
>  %0 = call i64* @testLLVMStructFuncCall(%0 { i32 10, i32 25 })
>  ret i64* %0
> }
> 2011-06-20 21:25:54.821 otest-x86_64[3369:707] 10 0
> /Users/mtindal/Projects/Silver/Tests/SVFunctionTests.m:576: error: -[SVFunctionTests testLLVMStructFuncCall] : Expected <35>, but was <10>
> Test Case '-[SVFunctionTests testLLVMStructFuncCall]' failed (0.016 seconds).
>
> The module dump suggests everything is right, i can see in the function call the struct with the values 10 and 25, but the function is only received the 10 for the x field, nothing for the y field.  Am I missing something?

The LLVM IR can't really completely represent calling conventions, so
there are hacks in the frontends for C-family languages to make the
generated code compatible with other compilers.  Take a look at the IR
clang generates for testLLVMStructFuncCall.

-Eli