[PATCH] D14497: [FunctionAttrs] Detect printf-like functions and propagate readnone+nocapture to variadic operands

[James Molloy via llvm-commits]

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If a function is just a wrapper around vsprintf or friends, it neither captures nor writes its arguments.

Because such a function is variadic, we are very conservative about any operand it is called with elsewhere in the compiler, so here if we can we should propagate readnone + nocapture to any operand to the function at all callsites.

In the future this can be extended to other v* functions in the standard library that have defined behavior on their operands, such as vscanf and friends (these do not capture, but do write).

Repository:
  rL LLVM

http://reviews.llvm.org/D14497

Files:
  lib/Transforms/IPO/FunctionAttrs.cpp
  test/Transforms/FunctionAttrs/varargs.ll

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