[mono][wasm] Rework the handling of GC references in AOTed code. #59352
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Previously, variables holding GC refs were marked volatile so they were loaded/stored to the C stack on every access. Since the stack is conservatively scanned, all the objects pointed to by it are pinned, so there is no need to load them on every access. Instead of marking them as volatile, allocate a 'gc pinning' area on the stack, and store ref variables to it after they are assigned. This improves code size and performance.
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This approach makes sense, but I wonder if LLVM's optimizer will outsmart us.
Also do we want to do this on non-wasm in the future? might avoid some spilling and copy_stack_data?
lewing
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imhameed
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Fixed by dotnet#59352 . Fixes dotnet#59228 .
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Can this be backported to rc2 too? |
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/backport to release/6.0-rc2 |
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Started backporting to release/6.0-rc2: https://github.com/dotnet/runtime/actions/runs/1256370822 |
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Previously, variables holding GC refs were marked volatile so they
were loaded/stored to the C stack on every access. Since the stack
is conservatively scanned, all the objects pointed to by it are pinned,
so there is no need to load them on every access. Instead of
marking them as volatile, allocate a 'gc pinning' area on the stack,
and store ref variables to it after they are assigned. This improves
code size and performance.