Defaults for parallel compile and link jobs about tc-build HOT 8 CLOSED

Building on a phone versus building on a laptop or server are two completely different use cases. The script aims to be as quick as possible which means building with as many compile and link jobs as ninja feels is reasonable by default. The -D option is there if it needs to be lowered but I disagree with setting any value to those options by default, especially given that LLVM doesn't.

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There is no default value of LLVM_PARALLEL_COMPILE_JOBS or LLVM_PARALLEL_LINK_JOBS:

https://github.com/llvm/llvm-project/blob/c37dd3b6d553d7ae3afaf677f1c6abdf6b1ec74e/llvm/cmake/modules/HandleLLVMOptions.cmake#L26-L52

https://llvm.org/docs/CMake.html#llvm-specific-variables

tc-build does not touch that value. I do not know what ninja's default parallelism but they do not recommend setting a -j value so it seems like they have their own heuristic.

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OK, I see that commit was for custom cmake options passing to tc-build.

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I suppose this is resolved then? Closing.

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IMHO - not really resolved.

I rebuild with safe parallel jobs setting for compile (=2) and link (=1).
It increased my build-time from usually 03:15 to 03:25 (mm:ss) - means 10 minutes.

The initial (Chinese) reporter was building with tc-build on an embedded system and had failures.

We should be user-friendly and offer/set safe settings.

My €0,02.

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One question:

When I pass compile/link jobs options and do a thinlto+pgo build - is that passed to stage2 and stage3?

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Yes, custom values are passed to all cmake invocations.

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