[llvm-commits] [llvm] r44825 - in /llvm/trunk: include/llvm/Target/TargetData.h lib/Target/TargetData.cpp

[Duncan Sands]

Hi Chris,

> Duncan, this patch gets llvm-gcc to build, but it still doesn't  
> answer the big question: why does TargetData contain information  
> about the host?

well, it needed to go somewhere.  Any suggestions for a better place?
Another possibility is to have a function isWrongEndian in target data,
which tells you if the target has opposite endianness to the host.

> I don't think this is the right approach.  Also, you   
> can get the host endianness without autoconf by using something  
> simple like:
> 
> bool islittleendian() {
>    union {
>      int i;
>      char c;
>    };
> 
>    i = 1;
>    return c;
> }

I have no particular opinion on this (except that it's amazing to me
that there's no standard way to query the compiler for this in C++ :) ).
Presumably the compiler will reduce this function to: return true; (or false)
at compile time, so there's no cost to your approach.  I suppose that plenty
of things that autoconf does could also be done in a special function like this,
yet they are left to autoconf - I have no idea what the criteria are for doing
something via autoconf or via a runtime test.  Having the function inline in a
header would have the advantage that the compiler would eliminate a bunch of code
in ExecutionEngine at runtime.  Since it seems that the autoconf solution is not
compatible with being exposed in a header, that suggests your solution is the way
to go.

Ciao,

Duncan.