[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.

3 files changed, 121 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
diff --git a/test/lit/passes/strip-eh.wast b/test/lit/passes/strip-eh.wast
new file mode 100644
index 000000000..dc394aebf
--- /dev/null
+++ b/test/lit/passes/strip-eh.wast
@@ -0,0 +1,117 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.
+;; RUN: wasm-opt %s -all --strip-eh -S -o - | filecheck %s
+
+;; Remove all EH instructions and tags. Converts 'throw's into 'unreachable's.
+
+(module
+  (tag $e-i32 (param i32))
+  (tag $e-f32 (param f32))
+
+  ;; CHECK:      (func $throw-i32 (type $none_=>_none)
+  ;; CHECK-NEXT:  (unreachable)
+  ;; CHECK-NEXT: )
+  (func $throw-i32
+    (throw $e-i32 (i32.const 0))
+  )
+  ;; CHECK:      (func $throw-f32 (type $none_=>_none)
+  ;; CHECK-NEXT:  (unreachable)
+  ;; CHECK-NEXT: )
+  (func $throw-f32
+    (throw $e-f32 (f32.const 0.0))
+  )
+
+  ;; CHECK:      (func $try-catch (type $none_=>_none)
+  ;; CHECK-NEXT:  (call $throw-i32)
+  ;; CHECK-NEXT: )
+  (func $try-catch
+    (try
+      (do
+        (call $throw-i32)
+      )
+      (catch $e-i32
+        (drop (pop i32))
+        (call $throw-f32)
+      )
+    )
+  )
+
+  ;; CHECK:      (func $try-catch2 (type $none_=>_none)
+  ;; CHECK-NEXT:  (call $throw-i32)
+  ;; CHECK-NEXT:  (call $throw-f32)
+  ;; CHECK-NEXT: )
+  (func $try-catch2
+    (try
+      (do
+        (call $throw-i32)
+        (call $throw-f32)
+      )
+      (catch $e-i32
+        (drop (pop i32))
+      )
+    )
+  )
+
+  ;; CHECK:      (func $try-catch-all (type $none_=>_none)
+  ;; CHECK-NEXT:  (unreachable)
+  ;; CHECK-NEXT: )
+  (func $try-catch-all
+    (try
+      (do
+        (throw $e-i32 (i32.const 0))
+      )
+      (catch_all
+        (call $throw-f32)
+      )
+    )
+  )
+
+  ;; CHECK:      (func $try-catch-nested (type $none_=>_none)
+  ;; CHECK-NEXT:  (call $throw-i32)
+  ;; CHECK-NEXT: )
+  (func $try-catch-nested
+    (try
+      (do
+        (try
+          (do
+            (call $throw-i32)
+          )
+          (catch $e-i32
+            (drop (pop i32))
+          )
+        )
+      )
+      (catch_all
+        (try
+          (do
+            (call $throw-f32)
+          )
+          (catch_all
+            (call $throw-f32)
+          )
+        )
+      )
+    )
+  )
+
+  ;; CHECK:      (func $try-unreachable-body (type $none_=>_i32) (result i32)
+  ;; CHECK-NEXT:  (i32.add
+  ;; CHECK-NEXT:   (unreachable)
+  ;; CHECK-NEXT:   (i32.const 0)
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT: )
+  (func $try-unreachable-body (result i32)
+    (i32.add
+      ;; This becomes unreachable while the parent expects i32, so this requires
+      ;; refinalization.
+      (try (result i32)
+        (do
+          (throw $e-i32 (i32.const 0))
+        )
+        (catch $e-i32
+          (pop i32)
+        )
+      )
+      (i32.const 0)
+    )
+  )
+)