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Implement break opcode as trap #4511

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morganbr opened this issue Sep 15, 2017 · 2 comments
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Implement break opcode as trap #4511

morganbr opened this issue Sep 15, 2017 · 2 comments
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arch-wasm up-for-grabs

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@morganbr
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Implement the break opcode. This normally breaks in a debugger, but that doesn't seem to be possible in WebAssembly, so we should start by implementing it as a trap. The method that handles the break opcode is

corert/src/ILCompiler.WebAssembly/src/CodeGen/ILToWebAssemblyImporter.cs

Line 270 in e6d0a93

private void ImportBreak()

@morganbr
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llvm.debugtrap might even stop the debugger correctly.

@morganbr morganbr mentioned this issue Dec 30, 2017
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@Blealtan
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Blealtan commented Feb 3, 2018

Experimented on @llvm.debugtrap. Emscripten generates it to a call to imported function asm2wasm.debugger, which is in turn implemented in js as the js statement debugger;; LLVM generates it into instruction unreachable, which is implemented in browsers as trap. As currently this is the only two implementation that generate LLVM IR directly into WASM, using @llvm.debugtrap intrinsic should be the best manner. Working on this.

Blealtan added a commit to Blealtan/corert that referenced this issue Feb 3, 2018
@Blealtan
Implement break opcode as llvm.debugtrap.
748d9bb 
In Emscripten, `llvm.debugtrap` is implemented as a round-trip call to
`debugger;` statement JavaScript which will invoke debugger in browsers;
and in LLVM it's implemented as `unreachable` instruction of WASM. This
should be a better match than `llvm.trap` on `break` opcode semantics.

Fix dotnet#4511
@Blealtan Blealtan mentioned this issue Feb 4, 2018
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