[all-commits] [llvm/llvm-project] 6bbf7f: [WebAssembly] Add assembly support for final EH pr...

[Heejin Ahn via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 6bbf7f06d8e4e84bbda9027252b26a0d9ae10cde
      https://github.com/llvm/llvm-project/commit/6bbf7f06d8e4e84bbda9027252b26a0d9ae10cde
  Author: Heejin Ahn <aheejin at gmail.com>
  Date:   2024-09-10 (Tue, 10 Sep 2024)

  Changed paths:
    M llvm/include/llvm/BinaryFormat/Wasm.h
    M llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmParser.cpp
    M llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyInstPrinter.cpp
    M llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyInstPrinter.h
    M llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCTargetDesc.h
    M llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCTypeUtilities.h
    M llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
    M llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
    M llvm/lib/Target/WebAssembly/WebAssemblyISelDAGToDAG.cpp
    M llvm/lib/Target/WebAssembly/WebAssemblyInstrControl.td
    M llvm/lib/Target/WebAssembly/WebAssemblyLateEHPrepare.cpp
    M llvm/lib/Target/WebAssembly/WebAssemblyMCInstLower.cpp
    M llvm/lib/Target/WebAssembly/WebAssemblyUtilities.cpp
    M llvm/test/CodeGen/WebAssembly/exception-legacy.ll
    A llvm/test/CodeGen/WebAssembly/exception.ll

  Log Message:
  -----------
  [WebAssembly] Add assembly support for final EH proposal (#107917)

This adds the basic assembly generation support for the final EH
proposal, which was newly adopted in Sep 2023 and advanced into Phase 4
in Jul 2024:

https://github.com/WebAssembly/exception-handling/blob/main/proposals/exception-handling/Exceptions.md

This adds support for the generation of new `try_table` and `throw_ref`
instruction in .s asesmbly format. This does NOT yet include
- Block annotation comment generation for .s format
- .o object file generation
- .s assembly parsing
- Type checking (AsmTypeCheck)
- Disassembler
- Fixing unwind mismatches in CFGStackify

These will be added as follow-up PRs.

---

The format for `TRY_TABLE`, both for `MachineInstr` and `MCInst`, is as
follows:
```
TRY_TABLE type number_of_catches catch_clauses*
```
where `catch_clause` is
```
catch_opcode tag+ destination
```
`catch_opcode` should be one of 0/1/2/3, which denotes
`CATCH`/`CATCH_REF`/`CATCH_ALL`/`CATCH_ALL_REF` respectively. (See
`BinaryFormat/Wasm.h`) `tag` exists when the catch is one of `CATCH` or
`CATCH_REF`.
The MIR format is printed as just the list of raw operands. The
(stack-based) assembly instruction supports pretty-printing, including
printing `catch` clauses by name, in InstPrinter.

In addition to the new instructions `TRY_TABLE` and `THROW_REF`, this
adds four pseudo instructions: `CATCH`, `CATCH_REF`, `CATCH_ALL`, and
`CATCH_ALL_REF`. These are pseudo instructions to simulate block return
values of `catch`, `catch_ref`, `catch_all`, `catch_all_ref` clauses in
`try_table` respectively, given that we don't support block return
values except for one case (`fixEndsAtEndOfFunction` in CFGStackify).
These will be omitted when we lower the instructions to `MCInst` at the
end.

LateEHPrepare now will have one more stage to covert
`CATCH`/`CATCH_ALL`s to `CATCH_REF`/`CATCH_ALL_REF`s when there is a
`RETHROW` to rethrow its exception. The pass also converts `RETHROW`s
into `THROW_REF`. Note that we still use `RETHROW` as an interim pseudo
instruction until we convert them to `THROW_REF` in LateEHPrepare.

CFGStackify has a new `placeTryTableMarker` function, which places
`try_table`/`end_try_table` markers with a necessary `catch` clause and
also `block`/`end_block` markers for the destination of the `catch`
clause.

In MCInstLower, now we need to support one more case for the multivalue
block signature (`catch_ref`'s destination's `(i32, exnref)` return
type).

InstPrinter has a new routine to print the `catch_list` type, which is
used to print `try_table` instructions.

The new test, `exception.ll`'s source is the same as
`exception-legacy.ll`, with the FileCheck expectations changed. One
difference is the commands in this file have `-wasm-enable-exnref` to
test the new format, and don't have `-wasm-disable-explicit-locals
-wasm-keep-registers`, because the new custom InstPrinter routine to
print `catch_list` only works for the stack-based instructions (`_S`),
and we can't use `-wasm-keep-registers` for them.

As in `exception-legacy.ll`, the FileCheck lines for the new tests do
not contain the whole program; they mostly contain only the control flow
instructions for readability.



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