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[docs] Rewrite cmake LLVM_RAM_PER_?_JOB description #88570

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Apr 22, 2024
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[docs] Rewrite cmake LLVM_RAM_PER_?_JOB description #88570

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[docs] Rewrite cmake LLVM_RAM_PER_?_JOB description
urnathan Apr 12, 2024
1dd6a9c
Augment debug build memory use
urnathan Apr 22, 2024
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42 changes: 17 additions & 25 deletions llvm/docs/CMake.rst
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Expand Up @@ -754,36 +754,28 @@ enabled sub-projects. Nearly all of these variable names begin with
during the build. Enabling this option can significantly speed up build times
especially when building LLVM in Debug configurations.

**LLVM_PARALLEL_COMPILE_JOBS**:STRING
Define the maximum number of concurrent compilation jobs.

**LLVM_PARALLEL_LINK_JOBS**:STRING
Define the maximum number of concurrent link jobs.

**LLVM_PARALLEL_TABLEGEN_JOBS**:STRING
Define the maximum number of concurrent tablegen jobs.
**LLVM_PARALLEL_{COMPILE,LINK,TABLEGEN}_JOBS**:STRING
Limit the maximum number of concurrent compilation, link or
tablegen jobs respectively. The default total number of parallel jobs is
determined by the number of logical CPUs.

**LLVM_PROFDATA_FILE**:PATH
Path to a profdata file to pass into clang's -fprofile-instr-use flag. This
can only be specified if you're building with clang.

**LLVM_RAM_PER_COMPILE_JOB**:STRING
Calculates the amount of Ninja compile jobs according to available resources.
Value has to be in MB, overwrites LLVM_PARALLEL_COMPILE_JOBS. Compile jobs
will be between one and amount of logical cores.

**LLVM_RAM_PER_LINK_JOB**:STRING
Calculates the amount of Ninja link jobs according to available resources.
Value has to be in MB, overwrites LLVM_PARALLEL_LINK_JOBS. Link jobs will
be between one and amount of logical cores. Link jobs will not run
exclusively therefore you should add an offset of one or two compile jobs
to be sure its not terminated in your memory restricted environment. On ELF
platforms also consider ``LLVM_USE_SPLIT_DWARF`` in Debug build.

**LLVM_RAM_PER_TABLEGEN_JOB**:STRING
Calculates the amount of Ninja tablegen jobs according to available resources.
Value has to be in MB, overwrites LLVM_PARALLEL_TABLEGEN_JOBS. Tablegen jobs
will be between one and amount of logical cores.
**LLVM_RAM_PER_{COMPILE,LINK,TABLEGEN}_JOB**:STRING
Limit the number of concurrent compile, link or tablegen jobs
respectively, depending on available physical memory. The value
specified is in MB. The respective
``LLVM_PARALLEL_{COMPILE,LINK,TABLEGEN}_JOBS`` variable is
overwritten by computing the memory size divided by the
specified value. The largest memory user is linking, but remember
that jobs in the other categories might run in parallel to the link
jobs, and you need to consider their memory requirements when
in a memory-limited environment. Using a
``-DLLVM_RAM_PER_LINK_JOB=10000`` is a good approximation. On ELF
platforms debug builds can reduce link-time memory pressure by also
using ``LLVM_USE_SPLIT_DWARF``.

**LLVM_REVERSE_ITERATION**:BOOL
If enabled, all supported unordered llvm containers would be iterated in
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