[docs] Added solutions to slow build under common problems.

I added a list of options to configure should someone have issues with
long build time or running out of memory. This was added under common
problems in the getting started section of the documentation.

Reviewed By: Meinersbur, dim, e-leclercq

Differential Revision: https://reviews.llvm.org/D75425

diff --git a/llvm/docs/GettingStarted.rst b/llvm/docs/GettingStarted.rst
index 0ede510..60b0bbf 100644 (file)
--- a/llvm/docs/GettingStarted.rst
+++ b/llvm/docs/GettingStarted.rst
@@ -1095,6 +1095,61 @@ If you are having problems building or using LLVM, or if you have any other
 general questions about LLVM, please consult the `Frequently Asked
 Questions <FAQ.html>`_ page.
 
+If you are having problems with limited memory and build time, please try
+building with ninja instead of make. Please consider configuring the
+following options with cmake:
+
+ * -G Ninja
+   Setting this option will allow you to build with ninja instead of make.
+   Building with ninja significantly improves your build time, especially with
+   incremental builds, and improves your memory usage.
+
+ * -DLLVM_USE_LINKER
+   Setting this option to either gold or lld will significantly improve
+   performance. In the case that you are compiling lld, you may wish to use the
+   gold linker as a faster alternative.
+
+ * -DCMAKE_BUILD_TYPE
+   This option defaults to Debug; however, this may consume more memory during
+   the linking phase. So, you may wish to use the build type Release. Another
+   build type you may wish to consider is release-with-asserts which compiles at
+   nearly the same rate as the Release build; however, it may not be as easy
+   to debug. MinSizeRel is another build type you may wish to consider, if you
+   are still having problems with slow build time.
+
+ * -DLLVM_PARALLEL_LINK_JOBS
+   Set this equal to number of jobs you wish to run simultaneously. This is
+   similar to the -j option used with make, but only for link jobs. This option
+   is of course only meaningful if you plan to build with ninja. You may wish to
+   use a very low number of jobs, as this will greatly reduce the amount memory
+   used during the build process. If you have limited memory, you may wish to
+   set this to 1.
+
+ * -DLLVM_TARGETS_TO_BUILD
+   Set this equal to the target you wish to build. You may wish to set this to
+   X86; however, you will find a full list of targets within the
+   llvm-project/llvm/lib/Target directory.
+
+ * -DLLVM_OPTIMIZED_TABLEGEN
+   Set this to ON to generate a fully optimized tablegen during build. This will
+   significantly improve your build time.
+
+ * -DLLVM_ENABLE_PROJECTS
+   Set this equal to the projects you wish to compile (e.g. clang, lld, etc.) If
+   compiling more than one project, deliniate the list with a semicolon. Should
+   you run into issues with the semicolon, try surrounding it with single quotes.
+
+ * -DCLANG_ENABLE_STATIC_ANALYZER
+   Set this option to OFF if you do not require the clang static analyzer. This
+   should improve your build time significantly.
+
+ * -DLLVM_USE_SPLIT_DWARF
+   Consider setting this to ON if you require a debug build, as this will ease
+   memory pressure on the linker. This will make linking much faster, as the
+   binaries will not contain any of the debug information; however, this will
+   generate the debug information in the form of a DWARF object file (with the
+   extension .dwo).
+
 .. _links:
 
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