[LLVMdev] Compiler Driver Decisions

[Chris Lattner]

On Wed, 4 Aug 2004, Reid Spencer wrote:
> I don't see why we have to maintain 100% compatibility with GCC. We're
> so incompatible in so many other ways that I don't see it as a
> necessity.

We are?  Currently you can just 'configure CC=llvmgcc' and stuff works.

> For example, we probably won't have all the -f and -X and -W
> options that GCC does. So, why can't we just DEFINE the optimization
> levels and be done with it? Its not like users of LLVM can just use
> their existing makefiles, they will have to make some adjustments.

They currently don't have to make these changes.  The -f flags that don't
make sense we can just ignore.  We support all of the -W flags I think.

> Also, I don't know of very many people that use -O0. Typical usage is
> either no -O option on the command line or -O2, -O3. In those typical
> use cases the driver will give them basically what they expect.

I agree this is much more common.

> So I propose:
>
> -O0 = zero optimization, raw output from the front end
> -O1 = default fast/lightweight optimization, emphasis on
>         making compilation faster

That is fine, but my point is that NO USER will ever care about -O0.
Since this is the case, why expose it at all?  It should only be exposed
for LLVM compiler hackers, which is why I suggested -On (later ammended to
-Onone).  I would not have a problem with it really being named something
without a -O prefix (-really-give-me-what-the-front-end-spits-out).

Given that, either -O0 and -O1 should do the same thing, or we should drop
one.

-Chris

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