Thread by @chapuni

#CLANG CAN BE BUILT WITHIN ONE MINUTE #LLVM

[2564/2564] Creating executable symlink bin/clang

real 0m56.685s
user 75m20.548s

* AWS c5a.24xlarge (96 vcpus)
* target=x86 MinSizeRel
* Using PGO+LTO clang and lld (up to 30% faster)

The trace.json is here; gist.github.com/chapuni/6b80af…

Tweaks in CMake part of the LLVM tree

* Enhanced LLVM_ENABLE_MODULES
** Generator and targets for explicit modules
* Modularized tblgen (invokes particular tblgen-emitters.so)
* Introduce obj.LLVMSupportLite for tblgen
* KILL target_link_libraries(PUBLIC) !!!IMPORTANT!!!

Tweaks to clang
* Introduce an option "Include headers textually instead of waiting for building modules"

Tweaks to clang-scan-deps

* Introduce format=Ninja for dyndep
** Add an interface to files to be generated
** Mark modules as "optional order-only deps"
* Use temporary module cache dir in minimized mode
* Add an option to enumerate modules from modulemap along include path

Tweaks to CMake

* Introduce a behavior to discover order-only deps on generated headers and convert them to ninja dyndep

Tweaks to Ninja-build

* Depth and cost based critical path scheduler (same as @thakis worked in 2014)

@thakis * Introduce "Optional order-only deps". They trigger dependent actions but don't wait for them.
They start as low priority. When all optional deps are resolved, their priorities become higher.
A compilation unit may start without waiting for building modules.

==TODO==

* Split X86ISelLowering.cpp
* Add to clang-scan-deps, "Fast and shallow lexical scanner"

Thank you.