[LLVMdev] Integer handling

[Matt Giuca]

OvermindDL1 wrote:
> 
> I know why it was removed, and it does make sense, just would be nice
> if there was an option to be able to get two pointer to a specific
> llvm::IntegerType, functionally they would be identical, but for user
> code (hence, my code) would be useful as I could match it for the
> different ones at generate different code for each.
> 
Well a language doesn't need to know whether an int is signed or unsigned if
all the operators are aware of the sign of its operands. Such is the case
with most assembly languages, and now LLVM. It makes the assembly cleaner
(because types are used only for checking, not for overloading operations).
And it seems you're going this way with your language (based on what you
said in the most recent post).

The thing is that high level languages really should encode signed/unsigned
into the type system (or simply deal only with signed integers, as many
languages do). You don't want your human programmers having to worry about
the signedness of an int each time they do anything with it.


OvermindDL1 wrote:
> 
> With some discussion with others I think we came up with an acceptable
> method (which allows me to completely kill my type duplication system,
> thank god).
> *snip*
> Either way, what do you think of the above style for handling integers
> now, think it will work?  See any major issues with it?  You think
> people would have trouble using that style?
> 

Well it will certainly work, but it's a pretty low-level / unsafe feature to
have in any language higher than assembly language. I wouldn't like it if I
was a user. But at least if I want to I can pretend there aren't any
unsigned ints and go about my merry way (so that's OK, the only problem is
when I actually want to use an unsigned int).

The thing is, practically any language higher than assembly is going to
require a type system, and that type system is almost certainly going to be
different to LLVM's. (eg. How do you distinguish dynamic arrays from
pointers? How do you give names to structure types? How do you distinguish
characters from i8s? Strings from arrays of i8s?) LLVM can't possibly
provide a rich enough type system for all the front-end languages; its type
system isn't designed to be used that way. The cleanest compiler design (in
my opinion) will have a completely type-checked program before it touches
the LLVM API at all. The compiler should then always generate type-correct
LLVM code (so your users should never see LLVM type errors, if your compiler
is behaving correctly).
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