[docs][NFC] Add usage instructions for FatLTO #75853
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We included these in the commit message when we added `-ffat-lto-objects`, but they should be in the documentation as well.
llvm/docs/FatLTO.rst
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| .. code-block:: console | ||
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| $ clang -fno-lto -ffat-lto-objects -fuse-ld=lld foo.c |
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This is just a nit, but would it be possible to use example.c instead of foo.c here and below?
llvm/docs/FatLTO.rst
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| no effect. | ||
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| Compile and link. Use the object code from the fat object without LTO. |
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I'm not sure these "compile and link" examples make a lot of sense. I think fat LTO is only meaningful if compile and link is separate.
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Yeah, I'll revise the examples to have a common first compile step and then different link steps.
llvm/docs/FatLTO.rst
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| .. code-block:: console | ||
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| $ clang -flto=thin -ffat-lto-objects -funified-lto -fuse-ld=lld foo.c |
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Isn't -funified-lto the default/required for fat LTO now? I'd expect the flag to have no additional effect.
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Ah, good point. Thanks.
Rename foo.c to example.c Remove UnifiedLTO examples, since FatLTO always uses that pipeline now.
llvm/docs/FatLTO.rst
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| @@ -76,3 +76,40 @@ Supported File Formats | |||
| The current implementation only supports ELF files. At time of writing, it is | |||
| unclear if it will be useful to support other object file formats like ``COFF`` | |||
| or ``Mach-O``. | |||
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| Usage | |||
| =========== | |||
llvm/docs/FatLTO.rst
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| .. code-block:: console | ||
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| $ clang -flto -ffat-lto-objects example.c -o example.o |
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Good catch. Thank you!
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| .. code-block:: console | ||
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| $ clang -fno-lto -ffat-lto-objects -fuse-ld=lld example.o |
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The description can state that -ffat-lto-objects is a no-op for linking when -fno-lto is specified.
llvm/docs/FatLTO.rst
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| Usage | ||
| =========== | ||
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| Users are expected to pass ``-ffat-lto-objects`` to clang in addition to one of |
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Clang users can specify -ffat-lto-objects along with -flto or -flto=thin. Without the -flto flag, -ffat-lto-objects has no effect.
We included these in the commit message when we added
-ffat-lto-objects, but they should be in the documentation as well.