[llvm] r182991 - X86: change MOV64ri64i32 into MOV32ri64

[David Blaikie]

On Fri, May 31, 2013 at 5:14 AM, Tim Northover <t.p.northover at gmail.com> wrote:
>> X86: change MOV64ri64i32 into MOV32ri64
>
> Hmm, it seems this broke the gdb 7.5 bot:
> http://lab.llvm.org:8011/builders/clang-x86_64-ubuntu-gdb-75/builds/5399.
>
> It looks like the test itself is dodgy: it consists of a few inline
> asm blocks, marked to clobber %eax and so on. However, it expects the
> compiler won't use those registers in *between* either. Previously
> this was true, but now on -O0 instead of:
>     movl $data, %r9d
> we produce:
>     movl $data, %eax
>     movl %eax, %r9d
>
> The extra instruction goes away (as it should) at higher
> optimisations, and I think it's perfectly valid, but the test doesn't
> like it.
>
> Can we XFAIL individual tests on this gdb7.5 bot, or do we usually do
> something else? I can't believe this hasn't come up before.

As you can see in the tests, this has come up before (these were
failing already when I started running the GDB 7.5 test suite against
Clang) - the xfails marked with "test is oversensitive to register
allocation/unoptimized code" represented the previous failures.

In light of this new change I've just given up & marked the tests as
not to be run at all (r183027).

If someone wants to argue that we should be preserving those registers
- I'm all ears & I can update the tests (though this probably
shouldn't be tested by our debug info tests anyway - we should have
other tests for it) & remember, this invariant was already not held,
just to a lesser degree of breakage - so we'd want to consider going
back & fixing that too.

>
> Cheers.
>
> Tim.
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