[wasm] Enable --gc-sections for WebAssembly by default
#71768
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This change enables the `--gc-sections` linker flag for WebAssembly targets by default. This flag has been disabled because it did not respect `llvm.used` and it caused stripping `swift5` metadata sections even though they were used through encapsulation symbols (a.k.a `__start`/`__stop`). The issue has been fixed in the LLVM side (llvm/llvm-project@ba3c1f9) by adding new segment flags to the WebAssembly object file format.
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This effectively reverts 3a366cc. After swiftlang/swift#71768, we don't have any reason to disable `--gc-sections` for WebAssembly targets. Note that the new wasm segment flags are only supported by the latest LLVM and wasm-ld, but we can assume that toolchains or Swift SDKs for WebAssembly have wasm-ld built from the latest LLVM.
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This effectively reverts 3a366cc. After swiftlang/swift#71768, we don't have any reason to disable `--gc-sections` for WebAssembly targets. Note that the new wasm segment flags are only supported by the latest LLVM and wasm-ld, but we can assume that toolchains or Swift SDKs for WebAssembly have wasm-ld built from the latest LLVM.
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MaxDesiatov
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Enable `--gc-sections` back for WebAssembly targets ### Motivation: We disabled `--gc-sections` for Wasm targets due to a lack of features in the object file format. However, we recently added the missing piece in wasm object file format, so we no longer have any reason to disable it. ### Modifications: This effectively reverts 3a366cc. After swiftlang/swift#71768, we don't have any reason to disable `--gc-sections` for WebAssembly targets. Note that the new wasm segment flags are only supported by the latest LLVM and wasm-ld, but we can assume that toolchains or Swift SDKs for WebAssembly have wasm-ld built from the latest LLVM. ### Result: Allow dead code stripping at link time for WebAssembly targets.
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May 15, 2024
Enable `--gc-sections` back for WebAssembly targets ### Motivation: We disabled `--gc-sections` for Wasm targets due to a lack of features in the object file format. However, we recently added the missing piece in wasm object file format, so we no longer have any reason to disable it. ### Modifications: This effectively reverts 3a366cc. After swiftlang/swift#71768, we don't have any reason to disable `--gc-sections` for WebAssembly targets. Note that the new wasm segment flags are only supported by the latest LLVM and wasm-ld, but we can assume that toolchains or Swift SDKs for WebAssembly have wasm-ld built from the latest LLVM. ### Result: Allow dead code stripping at link time for WebAssembly targets.
furby-tm
pushed a commit
to wabiverse/swift-package-manager
that referenced
this pull request
May 15, 2024
Enable `--gc-sections` back for WebAssembly targets ### Motivation: We disabled `--gc-sections` for Wasm targets due to a lack of features in the object file format. However, we recently added the missing piece in wasm object file format, so we no longer have any reason to disable it. ### Modifications: This effectively reverts 3a366cc. After swiftlang/swift#71768, we don't have any reason to disable `--gc-sections` for WebAssembly targets. Note that the new wasm segment flags are only supported by the latest LLVM and wasm-ld, but we can assume that toolchains or Swift SDKs for WebAssembly have wasm-ld built from the latest LLVM. ### Result: Allow dead code stripping at link time for WebAssembly targets.
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This change enables the
--gc-sectionslinker flag for WebAssembly targets by default. This flag has been disabled because it did not respectllvm.usedand it caused strippingswift5metadata sections even though they were used through encapsulation symbols (a.k.a__start/__stop).The issue has been fixed in the LLVM side (llvm/llvm-project@ba3c1f9) by adding new segment flags to the WebAssembly object file format, which is represented by
"R"flag in assembly orllvm.usedin LLVM IR.