llvm dev - Feb 2007 - [LLVMdev] another problem with function arguments aligment

The ARM EABI (AAPCS) defines:
- i64 values are 8-bytes aligned
- "The alignment of an aggregate shall be the alignment of its
most-aligned component."

So,

struct ss {
  int x;
  int y;
};

void f(int a, struct ss b);
r0 <- a
r1-r2 <- b

void g(int a, long long b);
r0 <- a
r2-r3 <- b

The problem is: llvm-gcc generates the same bytecode for both functions:

declare void @f(i32, i64)
declare void @g(i32, i64)

I can't differ an i64 argument from a struct argument.


Lauro

This is a known deficiency of llvm which we haven't had time to deal  
with. At llvm level, function arguments are lowered to integer types  
so some of these type information are lost.

I think adding a short term workaround is possible until we fix this  
"the right way". It involves adding the alignment information to  
ParameterAttributes. This will involve llvm language level and llvm- 
gcc changes.

Evan

On Feb 26, 2007, at 6:41 AM, Lauro Ramos Venancio wrote:
> The ARM EABI (AAPCS) defines:
> - i64 values are 8-bytes aligned
> - "The alignment of an aggregate shall be the alignment of its
> most-aligned component."
>
> So,
>
> struct ss {
>   int x;
>   int y;
> };
>
> void f(int a, struct ss b);
> r0 <- a
> r1-r2 <- b
>
> void g(int a, long long b);
> r0 <- a
> r2-r3 <- b
>
> The problem is: llvm-gcc generates the same bytecode for both  
> functions:
>
> declare void @f(i32, i64)
> declare void @g(i32, i64)
>
> I can't differ an i64 argument from a struct argument.
>
>
> Lauro
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

On Mon, 26 Feb 2007, Lauro Ramos Venancio wrote:
> The problem is: llvm-gcc generates the same bytecode for both functions:
>
> declare void @f(i32, i64)
> declare void @g(i32, i64)
>
> I can't differ an i64 argument from a struct argument.
Oops.  You can fix this by changing llvm-gcc: gcc/llvm-abi.h

Grep for instances of Int64Ty there.  I can help answer any q's you might 
have.

-Chris

-- 
http://nondot.org/sabre/
http://llvm.org/

I think, we must move function arguments lowering from frontend to
LLVM core. This lowering is generating machine dependent bytecode. See
http://llvm.org/bugs/show_bug.cgi?id=1230

Lauro

2007/2/26, Chris Lattner <sabre at nondot.org>:
> On Mon, 26 Feb 2007, Lauro Ramos Venancio wrote:
> > The problem is: llvm-gcc generates the same bytecode for both
functions:
> >
> > declare void @f(i32, i64)
> > declare void @g(i32, i64)
> >
> > I can't differ an i64 argument from a struct argument.
>
> Oops.  You can fix this by changing llvm-gcc: gcc/llvm-abi.h
>
> Grep for instances of Int64Ty there.  I can help answer any q's you
might
> have.
>
> -Chris
>
> --
> http://nondot.org/sabre/
> http://llvm.org/
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>