[PATCH] D25854: [lto] Kill undefined extern_weak declarations before opt

[Evgeniy Stepanov via llvm-commits]

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If an extern_weak declaration is resolved as undefined, RAUW it with
a null pointer and remove it from the module before running LTO
optimizations.

Besides the obvious codegen improvement, it allows CFI to avoid
generating jump tables for such functions (which can not be done
correctly, as a jump table entry can not be weak).


Repository:
  rL LLVM

https://reviews.llvm.org/D25854

Files:
  include/llvm/LTO/LTO.h
  lib/LTO/LTO.cpp
  test/LTO/Resolution/X86/weak.ll
  test/tools/gold/X86/comdat.ll
  test/tools/gold/X86/emit-llvm.ll
  test/tools/gold/X86/weak_undefined.ll
  tools/gold/gold-plugin.cpp
  tools/llvm-lto2/llvm-lto2.cpp

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