[LLVMdev] DebugFactory

[Devang Patel]

On Tue, Sep 22, 2009 at 4:49 PM, Talin <viridia at gmail.com> wrote:
>
>
> On Tue, Sep 22, 2009 at 9:21 AM, Devang Patel <devang.patel at gmail.com>
> wrote:
>>
>> On Tue, Sep 22, 2009 at 9:21 AM, Devang Patel <devang.patel at gmail.com>
>> wrote:
>> > On Tue, Sep 22, 2009 at 12:14 AM, Talin <viridia at gmail.com> wrote:
>> >> So, one feature of the late, lamented DebugInfoBuilder that I am
>> >> missing
>> >> quite badly, and which is not available in the current DIFactory, is
>> >> the
>> >> ability to specify structure offsets abstractly. The DebugFactory
>> >> requires that you pass in structure offset information as ints, whereas
>> >> DebugInfoBuilder had "offsetOf" and "alignOf" methods, similar to the
>> >> "sizeOf" trick, that would create the constants for you in a way that
>> >> didn't require your front end to know the sizes of things. So far I've
>> >> been able to avoid having any references to target machines in my
>> >> frontend, but now that I am trying to flesh out my debug info more
>> >> fully
>> >> I'm finding it hard to use DIFactory as-is.
>> >>
>> >> What I'd like to see is a set of alternative factory methods in
>> >> DIFactory, where you pass in an LLVM type, and possibly a GEP index,
>> >> plus all of the parameters that it can't figure out from looking at the
>> >> type. So you can eliminate the offset, size, and alignment parameters
>> >> since those can be figured out from the type.
>> >
>> > Is it true that DIFactory can figure this out with Target info in all
>> > cases ?
>>
>> oops... I meant to say "... without Target info..."
>>
> // Calculate the size of the specified LLVM type.
> Constant * DebugInfoBuilder::getSize(const Type * type) {
>     Constant * one = ConstantInt::get(Type::Int32Ty, 1);
>     return ConstantExpr::getPtrToInt(
>         ConstantExpr::getGetElementPtr(
>             ConstantPointerNull::get(PointerType::getUnqual(type)),
>             &one, 1), Type::Int32Ty);
> }
>
> Constant * DebugInfoBuilder::getAlignment(const Type * type) {
>     // Calculates the alignment of T using "sizeof({i8, T}) - sizeof(T)"
>     return ConstantExpr::getSub(
>         getSize(StructType::get(Type::Int8Ty, type, NULL)),
>         getSize(type));
> }
>
> This was code that was checked in before DebugInfoBuilder was replaced by
> DIFactory.

This adds code to find the info that FE knows anyway. That is
undesirable IMO. If there is a need, you can do this trick in your FE.


-- 
-
Devang