[PATCH] SimplifyCFG: recognise and simplify more no-op resumes.

[Duncan Sands]

Hi Peter,

> This is specifically targeted to identify the BB structure used
> by DragonEgg but it also resulted in a small (~4KB) decrease in
> binary size for a Clang-built Clang compiled with exceptions.
>
> http://llvm-reviews.chandlerc.com/D563
>
> Files:
>    lib/Transforms/Utils/SimplifyCFG.cpp
>    test/Transforms/SimplifyCFG/TrivialLPads.ll

it looks like it would be helpful if dragonegg didn't decompose the
exception pointer/filter pair and recompose them at the end; instead
it could pass them around as a pair and extract an element only when
it needs to be used individually.  For example, the pair would be passed
to the resume as a pair, rather than first reconstructing the pair from
its elements.  What do you think?

Ciao, Duncan.