[PATCH] Fix WinEHPrepare bug with multiple catch handlers

[Reid Kleckner]

Here's an idea. What if before outlining, we run mem2reg (see `llvm::PromoteMemToReg`) on all EH value objects? This should greatly simplify the existing preparation code, because we won't need to track stores of selectors and EH pointers anymore. Even at -O0, these allocas are not visible to the user, so removing them is useful. If the frontend produces IR that fails to promote, I think it's totally reasonable for WinEHPrepare to assert.


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http://reviews.llvm.org/D8682

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