[cfe-dev] How to add new target?

[Daniel Dunbar]

On Tue, Mar 30, 2010 at 7:44 AM, Artur Pietrek <pietreka at gmail.com> wrote:
>
>
> On Tue, Mar 30, 2010 at 2:25 PM, Artur Pietrek <pietreka at gmail.com> wrote:
>>
>> On Thu, Mar 25, 2010 at 4:21 PM, Daniel Dunbar <daniel at zuster.org> wrote:
>>>
>>> On Thu, Mar 25, 2010 at 5:33 AM, Artur Pietrek <pietreka at gmail.com>
>>> wrote:
>>> >> Hi Artur,
>>> >
>>> > Hi Daniel
>>> >
>>> >>
>>> >> > Hi all,
>>> >> > so after "greping" the code I was able to do (more or less)
>>> >> > everything I
>>> >> > wanted to do.
>>> >>
>>> >> As you have discovered, this stuff isn't very well documented yet. Do
>>> >> you feel like writing up a blurb we could add to our Internals Manual
>>> >> describing what you have discovered?
>>> >
>>> > I'll try when I'll make it work correct ;)
>>> >
>>> > BTW I've noticed strange behaviour. When I switched from llvm-gcc to
>>> > clang,
>>> > my benchmarks stopped working. When I compile simple code:
>>> >
>>> > char array[] =
>>> > "+0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz";
>>> >
>>> > int main() {
>>> >   return array[31];
>>> > }
>>> >
>>> > like this:
>>> > clang -ccc-host-triple mycpu -O0 -S hello.c -o hello.s
>>> >
>>> > The code is wrong, to be precise in one instruction I get
>>> > lbs $r16 = 0[$r17] instead of lbs $r16 = 31[$r17]
>>> >
>>> > but the code is correct when I do it like this:
>>> > clang -ccc-host-triple mycpu -O0 hello.c -c -emit-llvm -o hello.bc
>>> > llc -march=mycpu hello.bc -o hello.s
>>> >
>>> >
>>> > Am I missing something? Shouldn't these two be equivalent?
>>>
>>> Unfortunately, no. The driver sets a variety of options in the LLVM
>>> backend that you would need to pass to llc by hand. Try running
>>> $ clang -ccc-host-triple mycpu -O0 hello.c -c -emit-llvm -o hello.bc -###
>>> to see how clang is calling the compiler (clang -cc1), and look for -m
>>> arguments. For example, -mcpu sets the CPU to target, and other -m
>>> options do things like disable use of a frame pointer.
>>>
>>>  - Daniel
>>
>> Thanks for advice, there was a bug in relocation in my backend and indeed
>> clang was triggering it by passing different options than llc.
>>
>> Now I'm trying to find another bug. I don't know why I'm ending up with
>> reg to reg copy from 64bit to 32bit register class but only using clang and
>> turned on optimization (when i compile with llvm-gcc or again with clang to
>> bitcode and then using llc the problem does not occur).
>> I've tried to change options given to compiler, but this changes nothing.
>> The code I try to compile has castings from i8* to i64*.
>> Any ideas what could trigger that?
>> Is there a way to force clang to dump debug information similar to "llc
>> -debug"?
>
> So forget about that 64bit to 32bit question. It was a bug in conditional
> branch implementation.
>
> But still, is there a way to produce the debug output with clang as with
> llc?

Not currently, no. At the moment clang doesn't expose a way to pass
arbitrary options to LLVM's CommandLine module, which is how a lot of
the backend tools get those extra options. You can file a bug for this
if you like, its been on my list to add or think about.

 - Daniel

> Thanks
>