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This is a redo of #420, which was merged prematurely. The error we're seeing is: Looking at the LLVM source code, we see this error was introduced by llvm/llvm-project#89681, which first shipped in LLVM 19.1.0. The added test case says BOLT can't handle computed gotos in position independent code (PIC) (we use PIC since we build with -fPIC). We'll need to add |
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I diagnosed the BOLT issues and split those out into #463. I'm optimistic this will pass CI now. |
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LLVM 19 yields a compile error without these patches. Strictly speaking we may only need the final one. However there are conflicts unless we take all patches to `src/aarch64/sysv.S`. So we just take the 3 of them.
As part of this we also modernize the BOLT apply settings to follow the recommendations at https://llvm.org/devmtg/2024-03/slides/practical-use-of-bolt.pdf. This includes enabling support for loading hot code from a huge page at runtime. This should _just work_ and could result in perf wins via improved iTLB hit rate, etc.
zanieb
approved these changes
Jan 2, 2025
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This is a redo of #420, which was merged prematurely.
With the BOLT changes from #463 merged, LLVM 19 just works.
As part of this we also modernize the BOLT apply settings to follow the recommendations at https://llvm.org/devmtg/2024-03/slides/practical-use-of-bolt.pdf.
This includes enabling support for loading hot code from a huge page at runtime. This should just work and could result in perf wins via improved iTLB hit rate, etc.