llvm dev - Mar 2011 - [LLVMdev] DW_TAG_lexical_block structure in debug information

Hello,

The documentation for debug information
(http://llvm.org/docs/SourceLevelDebugging.html) says the structure of
block descriptors metadata is:

!3 = metadata !{
  i32,     ;; Tag = 11 + LLVMDebugVersion (DW_TAG_lexical_block)
  metadata,;; Reference to context descriptor
  i32,     ;; Line number
  i32      ;; Column number
}

However, looking at the generated metadata, there are 2 extra fields
not documented here. From the source code it appears to be a link to
the function holding the block, and a unique integer ID:

DILexicalBlock DIBuilder::createLexicalBlock(DIDescriptor Scope, DIFile File,
                                             unsigned Line, unsigned Col) {
  // Defeat MDNode uniqing for lexical blocks by using unique id.
  static unsigned int unique_id = 0;
  Value *Elts[] = {
    GetTagConstant(VMContext, dwarf::DW_TAG_lexical_block),
    Scope,
    ConstantInt::get(Type::getInt32Ty(VMContext), Line),
    ConstantInt::get(Type::getInt32Ty(VMContext), Col),
    File,
    ConstantInt::get(Type::getInt32Ty(VMContext), unique_id++)
  };
  return DILexicalBlock(MDNode::get(VMContext, &Elts[0],
array_lengthof(Elts)));
}

Is this an error in the documentation?

Thanks in advance,
Eli

On Mar 7, 2011, at 4:16 AM, Eli Bendersky wrote:
> Hello,
> 
> The documentation for debug information
> (http://llvm.org/docs/SourceLevelDebugging.html) says the structure of
> block descriptors metadata is:
> 
> !3 = metadata !{
>  i32,     ;; Tag = 11 + LLVMDebugVersion (DW_TAG_lexical_block)
>  metadata,;; Reference to context descriptor
>  i32,     ;; Line number
>  i32      ;; Column number
> }
> 
> However, looking at the generated metadata, there are 2 extra fields
> not documented here. From the source code it appears to be a link to
> the function holding the block, and a unique integer ID:
> 
> DILexicalBlock DIBuilder::createLexicalBlock(DIDescriptor Scope, DIFile
File,
>                                             unsigned Line, unsigned Col) {
>  // Defeat MDNode uniqing for lexical blocks by using unique id.
>  static unsigned int unique_id = 0;
>  Value *Elts[] = {
>    GetTagConstant(VMContext, dwarf::DW_TAG_lexical_block),
>    Scope,
>    ConstantInt::get(Type::getInt32Ty(VMContext), Line),
>    ConstantInt::get(Type::getInt32Ty(VMContext), Col),
>    File,
>    ConstantInt::get(Type::getInt32Ty(VMContext), unique_id++)
>  };
>  return DILexicalBlock(MDNode::get(VMContext, &Elts[0],
array_lengthof(Elts)));
> }
> 
> Is this an error in the documentation?
> 
These two  fields were added to support scopes inside template functions
(r107919).
I updated the docs today in r127249.

Thanks!
-
Devang