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compiler: pass i64 return value in an extra pointer param

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To support the WebAssembly<->JS barrier, return values also have to be
passed in memory. i64 return values are used by syscall/js, so must be
supported across this ABI barrier.
This commit is contained in:
Ayke van Laethem
2018-11-13 13:36:30 +01:00
parent 7d8b269f2e
commit 101d41dc58
3 changed files with 59 additions and 15 deletions
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docs/internals.rst
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@@ -147,6 +147,14 @@ somewhat compatible with the C calling convention but with a few quirks:
calling convention workaround may be removed. Also see `this wasm-bindgen
issue <https://github.com/rustwasm/wasm-bindgen/issues/35>`_.
* The WebAssembly target does not return variables directly that cannot be
handled by JavaScript (``struct``, ``i64``, multiple return values, etc).
Instead, they are stored into a pointer passed as the first parameter by the
caller.
This is the calling convention as implemented by LLVM, with the extension
that ``i64`` return values are returned in the same way as aggregate types.
* Some functions have an extra context parameter appended at the end of the
argument list. This only happens when both of these conditions hold: