Hello,
is there any documentation for LLVM codebase other than produced by doxygen?
The reason I'm asking is that doxygen docs are
(1) not very complete at the moment, as lot of classes don't even have a
description
(2) is generally not the best way to get high-level view of a big codebase.
As an example, consider this code:
%tmp.1 = setgt int %i, 0
br bool %tmp.1, label %then.0, label %else.0
It appears that Value* that corresponds to the %tmp.1 operand of the second
instruction is actually a pointer to Instruction* which represents the first
instruction.
This looks a nice design, given that all code is in SSA, but I've spend
considerable time today before understanding it, because I first tried to
look up a ways to find the instruction which defines tmp.1, then looked for
a method which returns destination of an instruction, and so on..
I realize all the developers must be busy, but some overview would be really
good.
- Volodya
Vladimir Prus wrote:
}
} Hello,
} is there any documentation for LLVM codebase other than produced by doxygen?
} The reason I'm asking is that doxygen docs are
} (1) not very complete at the moment, as lot of classes don't even have a
} description
} (2) is generally not the best way to get high-level view of a big codebase.
}
} As an example, consider this code:
}
} %tmp.1 = setgt int %i, 0
} br bool %tmp.1, label %then.0, label %else.0
}
} It appears that Value* that corresponds to the %tmp.1 operand of the second
} instruction is actually a pointer to Instruction* which represents the first
} instruction.
}
} This looks a nice design, given that all code is in SSA, but I've spend
} considerable time today before understanding it, because I first tried to
} look up a ways to find the instruction which defines tmp.1, then looked for
} a method which returns destination of an instruction, and so on..
}
There is a lot of documentation other than Doxygen. Try here:
http://llvm.cs.uiuc.edu/Documentation.html
There is a paper on LLVM's design. There's also the language reference
manual. And information on writing an LLVM pass.
I think the answer to your question above is: since LLVM is in SSA form,
you have one definition and multiple uses of a variable. Since names are
meaningless in LLVM, variables used in an instruction are pointers to
the definition of that varialbe, which is just an Instruction*. I
believe that they are Value* because the operands can be other than
Instructions (Constants, for instance).
I hope this helps :-)
-bw
--
|| "If wishes and buts were clusters of nuts, we'd all have a bowl of
|| granola!" - Mr. Jellineck
On Thu, 8 Apr 2004, Vladimir Prus wrote:> is there any documentation for LLVM codebase other than produced by doxygen?Yes, most definitely: http://llvm.cs.uiuc.edu/Documentation.html> The reason I'm asking is that doxygen docs are > (1) not very complete at the moment, as lot of classes don't even have a > description > (2) is generally not the best way to get high-level view of a big codebase.Quite true. Note that, in general, there are reasonable comments and descriptions of each interface at the top of each header file. I don't think that doxygen picks these descriptions up, so it might be good to look there. For example, contrast this: http://llvm.cs.uiuc.edu/doxygen/LoopInfo_8h-source.html to this: http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Loop.html> As an example, consider this code: > > %tmp.1 = setgt int %i, 0 > br bool %tmp.1, label %then.0, label %else.0 > > It appears that Value* that corresponds to the %tmp.1 operand of the second > instruction is actually a pointer to Instruction* which represents the first > instruction.This is exactly right.> This looks a nice design, given that all code is in SSA, but I've spend > considerable time today before understanding it, because I first tried to > look up a ways to find the instruction which defines tmp.1, then looked for > a method which returns destination of an instruction, and so on..This should be described in the developer's guide: http://llvm.cs.uiuc.edu/docs/ProgrammersManual.html#iterate_chains Like all documentation, it can probably be improved. If you would like to contribute a paragraph or two describing what you've learned, we would love to include it in the manual for others to learn from. :)> I realize all the developers must be busy, but some overview would be really > good.Sure, we think that documentation is really important. If you have any questions that are not covered in the documentation, please feel free to ask on the list. -Chris -- http://llvm.cs.uiuc.edu/ http://www.nondot.org/~sabre/Projects/
Chris Lattner wrote:> On Thu, 8 Apr 2004, Vladimir Prus wrote: > > is there any documentation for LLVM codebase other than produced by > > doxygen? > > Yes, most definitely: > http://llvm.cs.uiuc.edu/Documentation.htmlHmm.. I've looked at almost everything there... except for "Programmer Manual". Well, printing it now ;-)> > The reason I'm asking is that doxygen docs are > > (1) not very complete at the moment, as lot of classes don't even have a > > description > > (2) is generally not the best way to get high-level view of a big > > codebase. > > Quite true. Note that, in general, there are reasonable comments and > descriptions of each interface at the top of each header file. I don't > think that doxygen picks these descriptions up, so it might be good to > look there. For example, contrast this: > http://llvm.cs.uiuc.edu/doxygen/LoopInfo_8h-source.html > to this: > http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Loop.htmlOkay, understood.> > This looks a nice design, given that all code is in SSA, but I've spend > > considerable time today before understanding it, because I first tried to > > look up a ways to find the instruction which defines tmp.1, then looked > > for a method which returns destination of an instruction, and so on.. > > This should be described in the developer's guide: > http://llvm.cs.uiuc.edu/docs/ProgrammersManual.html#iterate_chains > > Like all documentation, it can probably be improved. If you would like to > contribute a paragraph or two describing what you've learned, we would > love to include it in the manual for others to learn from. :)Yes, I'll try to see if those paragraphs can be improved -- as written, then still don't say that operand can be just pointer to instruction.> > I realize all the developers must be busy, but some overview would be > > really good. > > Sure, we think that documentation is really important. If you have any > questions that are not covered in the documentation, please feel free to > ask on the list.Thanks, Volodya> > -Chris