[PATCH] D18990: [InstCombine] Remove trivially empty va_start/va_end and va_copy/va_end ranges.

[Arnaud A. de Grandmaison via llvm-commits]

aadg created this revision.
aadg added a reviewer: majnemer.
aadg added a subscriber: llvm-commits.
Herald added a subscriber: mcrosier.

When a va_start or va_copy is immediately followed by a va_end (ignoring
debug information or other start/end in between), then it is safe to
remove the pair. As this code shares some commonalities with the lifetime
markers, this has been factored to helper functions. In the va_copy
case a specific handling in needed because it does not have the same
prototype as the va_end.

This InstCombine pattern kicks-in 3 times when running the LLVM test
suite.

http://reviews.llvm.org/D18990

Files:
  lib/Transforms/InstCombine/InstCombineCalls.cpp
  lib/Transforms/InstCombine/InstCombineInternal.h
  test/Transforms/InstCombine/vararg.ll

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