[llvm-commits] [llvm] r141177 - in /llvm/trunk: lib/Transforms/Scalar/GVN.cpp test/Transforms/GVN/condprop.ll test/Transforms/GVN/phi-translate.ll

[Nick Lewycky]

On 11 October 2011 02:11, Duncan Sands <baldrick at free.fr> wrote:

> Hi David,
>
>  It's really close, but not quite. Given the attached llvm assembly, the
>> function
>> call is correctly devirtualized (but the branch is left in). But if you
>> comment
>> out the first ret void (in the vtable.ne <http://vtable.ne> block) &
>> comment in
>>
>> the unreachable instruction then the branch is removed by the simplifycfg
>> pass &
>> no interesting information about the condition is preserved for use by the
>> GVN
>> pass so the call is still indirect/virtual.
>>
>
> I thought there was a plan that a branch to a block containing only
> unreachable
> shouldn't be removed by the IR optimizers (instead codegen would remove
> it).  I
> even though Nick implemented this.  But apparently not...
>

Implemented but never committed. It had a lot of undesirable side-effects in
terms of preventing other optimizations from happening.

Nick
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