[PATCH] D23934: Add a -ffixed-date-time= flag that sets the initial value of __DATE__, __TIME__, __TIMESTAMP__

[Nico Weber via cfe-commits]

thakis created this revision.
thakis added a reviewer: rsmith.
thakis added a subscriber: cfe-commits.

This is useful for creating reproducible builds. Defining these via -D triggers warnings, and can cause bugs (presently, e.g. PR29119). It makes it also impossible to override __DATE__ and __TIME__ and forget __TIMESTAMP__.

__TIMESTAMP__ has slightly different semantics in that it's the timestamp of the current TU, not the time of compilation, but either meaning is bad for reproducible builds.

https://reviews.llvm.org/D23934

Files:
  include/clang/Driver/Options.td
  include/clang/Lex/PreprocessorOptions.h
  lib/Driver/Tools.cpp
  lib/Frontend/CompilerInvocation.cpp
  lib/Lex/PPMacroExpansion.cpp
  test/Preprocessor/fixed-date-time.cc

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