[all-commits] [llvm/llvm-project] 9724c3: [WebAssembly] Update WasmEHPrepare for the new spec

[Heejin Ahn via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 9724c3cff46fb9e333df7d27b44758b4aba07168
      https://github.com/llvm/llvm-project/commit/9724c3cff46fb9e333df7d27b44758b4aba07168
  Author: Heejin Ahn <aheejin at gmail.com>
  Date:   2021-01-08 (Fri, 08 Jan 2021)

  Changed paths:
    M clang/test/CodeGenCXX/wasm-eh.cpp
    M llvm/include/llvm/CodeGen/WasmEHFuncInfo.h
    M llvm/include/llvm/IR/IntrinsicsWebAssembly.td
    M llvm/lib/CodeGen/WasmEHPrepare.cpp
    M llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
    M llvm/lib/Target/WebAssembly/WebAssemblyInstrControl.td
    M llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll
    M llvm/test/CodeGen/WebAssembly/eh-lsda.ll
    M llvm/test/CodeGen/WebAssembly/exception.ll
    M llvm/test/CodeGen/WebAssembly/wasmehprepare.ll

  Log Message:
  -----------
  [WebAssembly] Update WasmEHPrepare for the new spec

Clang generates `wasm.get.exception` and `wasm.get.ehselector`
intrinsics, which respectively return a caught exception value (a
pointer to some C++ exception struct) and a selector (an integer value
that tells which C++ `catch` clause the current exception matches, or
does not match any).

WasmEHPrepare is a pass that does some IR-level preparation before
instruction selection. Previously one of things we did in this pass was
to convert `wasm.get.exception` intrinsic calls to
`wasm.extract.exception` intrinsics. Their semantics were the same
except `wasm.extract.exception` did not have a token argument. We
maintained these two separate intrinsics with the same semantics because
instruction selection couldn't handle token arguments. This
`wasm.extract.exception` intrinsic was later converted to
`extract_exception` instruction in instruction selection, which was a
pseudo instruction to implement `br_on_exn`. Because `br_on_exn` pushed
an extracted value onto the value stack after the `end` instruction of a
`block`, but LLVM does not have a way of modeling that kind of behavior,
so this pseudo instruction was used to pull an extracted value out of
thin air, like this:
```
block $l0
  ...
  br_on_exn $cpp_exception $l0
  ...
end
extract_exception ;; pushes values onto the stack
```

In the new spec, we don't need this pseudo instruction anymore because
`catch` itself returns a value and we don't have `br_on_exn` anymore. In
the spec `catch` returns multiple values (like `br_on_exn`), but here we
assume it only returns a single i32, which is sufficient to support C++.

So this renames `wasm.get.exception` intrinsic to `wasm.catch`. Because
this CL does not yet contain instruction selection for `wasm.catch`
intrinsic, all `RUN` lines in exception.ll, eh-lsda.ll, and
cfg-stackify-eh.ll, and a single `RUN` line in wasm-eh.cpp (which is an
end-to-end test from C++ source to assembly) fail. So this CL
temporarily disables those `RUN` lines, and for those test files without
any valid remaining `RUN` lines, adds a dummy `RUN` line to make them
pass. These tests will be reenabled in later CLs.

Reviewed By: dschuff, tlively

Differential Revision: https://reviews.llvm.org/D94039