[llvm-dev] How do set 'nest' addribute in an indirect call?

[Rodney M. Bates via llvm-dev]

Ping.

On 08/17/2017 05:15 PM, Rodney M. Bates via llvm-dev wrote:
> I need to set the 'next' attribute on a parameter.  If the function is to be
> directly called, i.e., a function constant, I am getting what I want as follows
> (using the C 'Core.h' binding)
>
> 1) Build a function type, using LLVMFunctionType.
> 2) Build a function value, passing the result of 1) to LLVMAddFunction
> 3) Go through the formal parameters of 2), using LLVMGet[First|Next]Param,
>    which give me a value for each formal
> 4) For the desired formal, pass it to LLVMAddAttribute.
>
> This results in compiled code that passes my parameter in the same way as gcc,
> giving the interoperability I need.
>
> For an indirect call, i.e., on a function whose address is runtime variable,
> I can't find any place/way to attach this attribute.  LLVMAddAttribute
> won't take a type.
>
> I don't see a way to construct a function value with a runtime variable
> address, that I could do 3) & 4) on.  (I already have an i8* pointer to
> the function code.)
>
> The comment on LLVMAddAttribute says  " Add an attribute to a function argument",
> which, to me, "argument" means an actual parameter.  But When I try that, I get
> an assertion failure, which I am having trouble interpreting:
>
> m3llvm: /home/rodney/proj/llvm/llvm-3.6.1/llvm-3.6.1.src/include/llvm/Support/Casting.h:237: typename cast_retty<X, Y *>::ret_type llvm::cast(Y *) [X = llvm::Argument, Y = llvm::Value]: Assertion `isa<X>(Val) && "cast<Ty>() argument of incompatible type!"' failed.
>
> My actual parameter is a load instruction, which I would expect to be a value.
> Its llvm type is i8*, but I don't think that is relevant.
>
> Here are some relevant debugger lines:
>
> (m3gdb) frame 7
> #7  0x00000000004264fd in M3CG_LLVM__InnerCallIndirect (self=16_0000000001b30830, proc=16_0000000001a7e388, t=Void,
>     cc=16_0000000001b07928, Nested=TRUE) at ../src/M3CG_LLVM.m3:4750
> 4750              LLVM.LLVMAddAttribute(actual.lVal, LLVM.NestAttribute);
> Current language:  auto; currently Modula-3
> (m3gdb) p M3CG_LLVM__DumpLvVal(actual.lVal)
>   %load_ind13 = load i8** %load_ind_toptr12
> $1 = <void>
> (m3gdb) p M3CG_LLVM__LvType(actual.lVal)
> $2 = 16_0000000001a78620
> (m3gdb) p M3CG_LLVM__DumpLvType($2)
> i8*
> $3 = <void>
> (m3gdb)
>
>

-- 
Rodney Bates
rodney.m.bates at acm.org