[EH] Add pass to remove EH instructions (#5770)

This pass strips all EH stuff, including EH instructions and tags, from
the input module and disables the EH feature from the features section.

1. This removes `catch` and `catch_all` blocks from the code. So
```wast
(try
  (do
    (some code)
  )
  (catch
    ...
  )
)
```
becomes just `(some code)`. Note that all `rethrow`s will be removed
with `catch`es. Note that all `rethrow`s will be removed with `catch`es.

2. This converts 'throw (...)` into `unreachable`. Note that `rethrows

3. This removes all tags from the module, which are unused anyway after
1 and 2.

4. This removes exception handling feature from the features section.

You can use the pass with
```console
$ wasm-opt --enable-exception-handling --strip-eh INPUT -o OUTPUT
```
This is not an optimization pass, so it is not run unless you specify
the pass explicitly.

This is in effect similar to Clang's `-fignore-exceptions`, in which you
can throw but it will result in a crash and we compile away all landing
pads. This can be used for people who don't (or can't) use
`-fignore-exceptions` in their build settings or who want to compile
away `catch` blocks later.

Closes emscripten-core/emscripten#19585.

2 files changed, 4 insertions, 0 deletions

diff --git a/test/lit/help/wasm-opt.test b/test/lit/help/wasm-opt.test
index 2e10ed073..30369e62f 100644
--- a/test/lit/help/wasm-opt.test
+++ b/test/lit/help/wasm-opt.test
@@ -452,6 +452,8 @@
 ;; CHECK-NEXT:
 ;; CHECK-NEXT:   --strip-dwarf                                 strip dwarf debug info
 ;; CHECK-NEXT:
+;; CHECK-NEXT:   --strip-eh                                    strip EH instructions
+;; CHECK-NEXT:
 ;; CHECK-NEXT:   --strip-producers                             strip the wasm producers section
 ;; CHECK-NEXT:
 ;; CHECK-NEXT:   --strip-target-features                       strip the wasm target features
diff --git a/test/lit/help/wasm2js.test b/test/lit/help/wasm2js.test
index 1766d771d..916dbbb4d 100644
--- a/test/lit/help/wasm2js.test
+++ b/test/lit/help/wasm2js.test
@@ -411,6 +411,8 @@
 ;; CHECK-NEXT:
 ;; CHECK-NEXT:   --strip-dwarf                                 strip dwarf debug info
 ;; CHECK-NEXT:
+;; CHECK-NEXT:   --strip-eh                                    strip EH instructions
+;; CHECK-NEXT:
 ;; CHECK-NEXT:   --strip-producers                             strip the wasm producers section
 ;; CHECK-NEXT:
 ;; CHECK-NEXT:   --strip-target-features                       strip the wasm target features