llvm dev - Jan 2007 - [LLVMdev] llc c backend can produce code that doesn't compile on gcc 4.x

Hello,

I would like to ask the llvm developers to have a look at http:// 
llvm.org/bugs/show_bug.cgi?id=918 .
This bug has been reported 4 month ago but is none the less a  
somewhat serious one.

Below I have pasted the test case and output of the issue running on  
my ppc machine.

thank you
Eric


pb:~ eric$ cat testme.ll;llvm-as -f testme.ll;llc -march=c -f  
testme.bc;gcc -c testme.cbe.c ;gcc --version;llc --version
%structtype_s = type { i32 }
%fixarray_array3 = type [3 x %structtype_s]

define i32 %witness(%fixarray_array3* %p) {
     %q = getelementptr %fixarray_array3* %p, i32 0, i32 0, i32 0
     %v = load i32* %q
     ret i32 %v
}
testme.cbe.c:106: error: array type has incomplete element type
testme.cbe.c:119: warning: conflicting types for built-in function  
'malloc'
powerpc-apple-darwin8-gcc-4.0.0 (GCC) 4.0.0 (Apple Computer, Inc.  
build 5026)
Copyright (C) 2005 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There  
is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR  
PURPOSE.

Low Level Virtual Machine (http://llvm.org/):
   llvm version 2.0cvs
   Optimized build with assertions.
pb:~ eric$
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Eric van Riet Paap wrote:
> *testme.cbe.c:106: error: array type has incomplete element type*
The problem code boils down to:

  /* Structure forward decls */
  struct l_structtype_s;

  /* Typedefs */
  typedef struct l_structtype_s l_fixarray_array3[3];

which is illegal C, but perfectly valid C++, and g++ accepts it.

The structure contents are defined right afterwards, but I assume that
the typedefs are used when emitting the structure contents? We may have
to put fully defined structures first and typedefs second.

Nick Lewycky

On Mon, 15 Jan 2007, Nick Lewycky wrote:
> Eric van Riet Paap wrote:
>> *testme.cbe.c:106: error: array type has incomplete element type*
>
> The problem code boils down to:
>
>  /* Structure forward decls */
>  struct l_structtype_s;
>
>  /* Typedefs */
>  typedef struct l_structtype_s l_fixarray_array3[3];
>
> which is illegal C, but perfectly valid C++, and g++ accepts it.
>
> The structure contents are defined right afterwards, but I assume that
> the typedefs are used when emitting the structure contents? We may have
> to put fully defined structures first and typedefs second.
Looks like it.  It sounds like the CBE should build an ordering of types, 
based on their nesting properties, then emit them in nesting order. 
Because all recursive types have to go through a pointer in C, we should 
get a dag of types, which is easy to emit.

Anyone want to take a crack at it?

-Chris

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