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[docs] [CMake] Change recommendations for how to use LLVM_DEFINITIONS

Authored by mstorsjo on May 24 2021, 1:28 PM.



LLVM_DEFINITIONS is a string variable containing a list of arguments
to pass to the compiler. When CMake's add_definitions is passed a
string variable, this is interpreted as one argument. To make it
behave properly, the string variable needs to be split into a list.

Despite the fact that add_definitions isn't supposed to be used like
the LLVM docs recommended, it worked fine in practice in many cases.
If the first argument in LLVM_DEFINITIONS is of the form -DFOO=42
instead of plain -DFOO, the rest of the string is treated as value
to this define. I.e. if LLVM_DEFINITIONS consists of -DFOO=42 -DBAR,
CMake ended up passing -DFOO="42 -DBAR" to the compiler.

for discussion on the matter.

Changing LLVM_DEFINITIONS to be a list variable would possibly be
more disruptive; instead keep the variable defined as before but
change the recommendation for how to use it. Then projects using it
can gradually be updated to follow the new recommendation.

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mstorsjo created this revision.May 24 2021, 1:28 PM
mstorsjo requested review of this revision.May 24 2021, 1:28 PM
Herald added a project: Restricted Project. · View Herald TranscriptMay 24 2021, 1:28 PM
phosek accepted this revision.May 24 2021, 4:07 PM


This revision is now accepted and ready to land.May 24 2021, 4:07 PM
This revision was landed with ongoing or failed builds.May 25 2021, 1:04 PM
This revision was automatically updated to reflect the committed changes.