llvm dev - Jun 2009 - [LLVMdev] Structure Returns

Hi,

In my LLVM IR I am returning a structure from a function but it gave me an
assertion failure when I was trying to compile the resulting bitcode.

Specifically, I had following function definition


define {i32,i32,i32} @func(i32 a)
{
.....
ret {i32,i32,i32} %retStruct
}


llc gave me following assertion failure:

Return operand#2 has unhandled type i32  in AnalyzeReturn function

On digging out from LLVM website, I found

"Note that the code generator does not yet fully support large return
values. The specific sizes that are currently supported are dependent on the
target. For integers, on 32-bit targets the limit is often 64 bits, and on
64-bit targets the limit is often 128 bits. For aggregate types, the current
limits are dependent on the element types; for example targets are often
limited to 2 total integer elements and 2 total floating-point elements."

So, does this mean that I can't have a return type with more than two
integers? Is there any other way to support longer return structure?

-- Kapil
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On Thu, Jun 25, 2009 at 10:49 AM, kapil anand<kapilanand2 at gmail.com>
wrote:
> Hi,
>
> In my LLVM IR I am returning a structure from a function but it gave me an
> assertion failure when I was trying to compile the resulting bitcode.
>
> Specifically, I had following function definition
>
>
> define {i32,i32,i32} @func(i32 a)
> {
> .....
> ret {i32,i32,i32} %retStruct
> }
>
>
> llc gave me following assertion failure:
>
> Return operand#2 has unhandled type i32  in AnalyzeReturn function
>
> On digging out from LLVM website, I found
>
> "Note that the code generator does not yet fully support large return
> values. The specific sizes that are currently supported are dependent on
the
> target. For integers, on 32-bit targets the limit is often 64 bits, and on
> 64-bit targets the limit is often 128 bits. For aggregate types, the
current
> limits are dependent on the element types; for example targets are often
> limited to 2 total integer elements and 2 total floating-point
elements."
>
> So, does this mean that I can't have a return type with more than two
> integers? Is there any other way to support longer return structure?
That's what it means (at least until someone like you contributes a
patch to support larger return structs). To work around it, imitate
what the C compiler does.

Try typing:

struct Big {
 int a, b, c;
};

struct Big foo() {
  struct Big result = {1, 2, 3};
  return result;
}


into http://llvm.org/demo/.