[docs][cmake] document LLVM_ENABLE_PLUGINS

[nickdesaulniers]

Summary

Looks like LLVM_ENABLE_PLUGINS was created in r212315.

Some additional info on plugins can be found:

• https://llvm.org/docs/GoldPlugin.html
• https://clang.llvm.org/docs/ClangPlugins.html
• https://chromium.googlesource.com/chromium/src/+/HEAD/docs/writing_clang_plugins.md

r260262 seems to indicate that LLVM_ENABLE_PLUGINS default value is
platform specific.

pr/41970

[srhines]

llvm/docs/CMake.rst

602

LLVM

[nickdesaulniers]

llvm/docs/CMake.rst

602

It was intentional; I think usually people try to load plugins through clang a la https://clang.llvm.org/docs/ClangPlugins.html.

I can change it to LLVM if you feel strongly about this. WDYT?

Also, should I maybe mention LLVM_ENABLE_PLUGINS on that page (and the LLVMGold one)?

[srhines]

llvm/docs/CMake.rst

602

Sorry, I forget that phabricator doesn't do intra-line highlights, and thus my message was misinterpreted. I wanted a fix for the capitalization of LLVM, since it isn't lowercase in this doc.

As far as the ClangPlugins.html page, I think that is generally user docs, so shouldn't be concerned with building your own LLVM distribution.

[nickdesaulniers]

• capitalize LLVM

[nathanchance]

Is there a point to adding this if it isn't a user selectable option? LLVM_ENABLE_PLUGINS doesn't have an option in any cmake files, it is only ever set.

[nickdesaulniers]

In D62218#1510979, @nathanchance wrote:

Is there a point to adding this if it isn't a user selectable option? LLVM_ENABLE_PLUGINS doesn't have an option in any cmake files, it is only ever set.

Huh, weird...

$ cd llvm/build
$ rm -rf *
$ cmake .. -DCMAKE_BUILD_TYPE=Release -G Ninja -DLLVM_ENABLE_LLD=ON -DLLVM_ENABLE_PROJECTS="clang;lld" -DLLVM_TARGETS_TO_BUILD="AArch64;ARM;X86" -DLLVM_ENABLE_PLUGINS="ON"
$ ninja check-llvm-bugpoint
...
[0/1] Running lit suite /android0/llvm-project/llvm/test/BugPoint
Testing Time: 0.11s
  Unsupported Tests  : 10

$ cmake .. -DCMAKE_BUILD_TYPE=Release -G Ninja -DCMAKE_C_COMPILER=/android1/android-master/prebuilts/clang/host/linux-x86/clang-r353983c/bin/clang -DCMAKE_CXX_COMPILER=/android1/android-master/prebuilts/clang/host/linux-x86/clang-r353983c/bin/clang++ -DLLVM_ENABLE_LLD=ON -DLLVM_ENABLE_PROJECTS="clang;lld" -DLLVM_TARGETS_TO_BUILD="AArch64;ARM;X86" -DLLVM_BUILD_LLVM_DYLIB="ON"
$ ninja check-llvm-bugpoint
[12/13] Running lit suite /android0/llvm-project/llvm/test/BugPoint
Testing Time: 1.24s
  Expected Passes    : 10

Guess I should have known that: https://github.com/ClangBuiltLinux/tc-build/commit/f0a88523bcfd60f649536a07f678e85ef31b4a2d. Thanks @nathanchance !

llvm/docs/CMake.rst

 
 **LLVM_TEMPORARILY_ALLOW_OLD_TOOLCHAIN**:BOOL
   If enabled, the compiler version check will only warn when using a toolchain
   which is about to be deprecated, instead of emitting an error.
 
 **LLVM_USE_NEWPM**:BOOL
   If enabled, use the experimental new pass manager.
 
+**LLVM_ENABLE_PLUGINS**::BOOL
+  If enabled, allows LLVM to load plugins, such as LLVMgold or custom Clang
+  plugins. Default value is platform specific.
+
 CMake Caches
 ============
 
 Recently LLVM and Clang have been adding some more complicated build system
 features. Utilizing these new features often involves a complicated chain of
 CMake variables passed on the command line. Clang provides a collection of CMake
 cache scripts to make these features more approachable.