Fast block return #78
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| @@ -1996,7 +1996,7 @@ run2: rounds | mock | | |||
| self run: [ mock selfSend ] rounds: rounds text: 'Self dispatch'. | |||
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| self run: [ mock invokeBlock: [nil] ] rounds: rounds text: 'Block invoke'. | |||
| self run: [ mock blockReturn ] rounds: rounds text: 'Block return'. | |||
| self run: [ 1 to: rounds do: [ :x | mock blockReturn ] ] rounds: 1 text: 'Block return'. | |||
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| @@ -127,13 +127,16 @@ if (USE_LLVM) | |||
| src/llstPass.cpp | |||
| src/llstDebuggingPass.cpp | |||
| ) | |||
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| add_library(trampoline "src/trampoline.cpp") | |||
| set_source_files_properties(src/trampoline.cpp PROPERTIES COMPILE_FLAGS "-freg-struct-return") | |||
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WTF, Дима. Я как бэ комменты оставил |
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Изменения по твоим комментариям надо оформить отдельным PR поверх |
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Original implementation uses exception API to perform far jump to dispatch
BlockReturninstruction. This work OK but is terribly slow. I mean REALLY slow, 10 times slower than the software implementation and 40 times slower than implementation proposed here.Current pull request implements
BlockReturnusing MRV technique to return several values in registers instead of stack. In our case result object is returned ineaxwhereas target context inedx(on x86 of course). Cascade block return is handled by simply propagating these two registers unchanged from inner stack frame to outer and so on. Typical overhead is onecmportestinstruction per message send and oneretinstruction per frame.We use use
-freg-struct-returntechnique which is uncommon in UNIX world and it's calling conventions, but is fully supported in GCC and clang depending on a compiler version.More portable implementation should pass return value using the stack (
sretin terms of LLVM) but this will be slower and will not handle cascade return in a straightforward way.