[llvm-commits] [llvm-gcc-4.2] r72505 - /llvm-gcc-4.2/trunk/README.LLVM

[Dan Gohman]

On May 27, 2009, at 11:43 PM, Duncan Sands wrote:

> Hi Dan,
>
>> +To build a compiler that targets 32-bit x86, the following options  
>> should be
>> +added to the configure line:
>> +  --target=i686-pc-linux-gnu --with-tune=generic --with- 
>> arch=pentium4
>> +You can select a different arch string if you prefer, but it's  
>> important to
>> +use this option to prevert llvm-gcc from defaulting to generic  
>> i386, which
>> +can lead to problems as llvm itself doesn't support x86 targets  
>> lower
>> +than i486.
>
> the default always worked for me.  Are you saying that if the target  
> is
> i386 then the generated code won't run on an i386, only i486 and  
> better?
> If so, why not just mention that.  I don't see why there is any need  
> to
> change how the compiler is configured though.


It is true that LLVM currently doesn't support actual i386.  I thought
I saw this documented somewhere once, though I can't find it now.

Configuring llvm-gcc properly is important so that the front-end
defines appropriate pre-defined subtarget macros.  These often
don't matter, but in some cases they do.

Dan