[PATCH] EH: Prune unreachable resume instructions during Dwarf EH preparation

[Reid Kleckner]

Hi majnemer,

Today a simple function that only catches exceptions and doesn't run
destructor cleanups ends up containing a dead call to _Unwind_Resume
(PR20300). We can't remove these dead resume instructions during normal
optimization because inlining might introduce additional landingpads
that do have cleanups to run. Instead we can do this during EH
preparation, which is guaranteed to run after inlining.

Fixes PR20300.

http://reviews.llvm.org/D7744

Files:
  include/llvm/CodeGen/Passes.h
  lib/CodeGen/CodeGen.cpp
  lib/CodeGen/DwarfEHPrepare.cpp
  lib/CodeGen/WinEHPrepare.cpp
  test/CodeGen/Mips/eh.ll
  test/CodeGen/X86/dwarf-eh-prepare.ll
  test/CodeGen/X86/gcc_except_table.ll
  test/CodeGen/X86/gcc_except_table_functions.ll
  test/CodeGen/XCore/exception.ll

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