[Wasm][IRGen] Add initial support for unconditional absolute function pointer #42094
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On some Harvard architectures like WebAssembly that allow sliding code and data address space offsets independently, it's impossible to make direct relative reference to code from data because the relative offset between them is not representable. Use absolute function references instead of relative ones on such targets.
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This was referenced Mar 30, 2022
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All code paths added in this change don't affect targets other than Wasm |
beccadax
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swiftlang#42094 added a new `IRGenOptions::CompactAbsoluteFunctionPointer` field, but did not initialize it. We subsequently started seeing flaky test failures in LLDB tests that tried to resolve relocations in metadata, so we think this may have resulted in the option sometimes being set to `true` in the REPL.
kateinoigakukun
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I added an assertion to catch new relative function pointers in swiftlang#42094, so we should enable assertions to utilize it while building stdlib and corelibs
This was referenced Apr 3, 2022
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I discussed this with @rjmccall and @jckarter on a forum thread,
and we've got a consensus on how to upstream the relative pointer
support for Wasm.
The runtime part and id resolution of KeyPath will come in another PR.
On some Harvard architectures like WebAssembly that allow sliding code
and data address space offsets independently, it's impossible to make
direct relative reference to code from data because the relative offset
between them is not representable.
Use absolute function references instead of relative ones on such targets.