DeadArgumentElimination: Remove removable effects (#4514)

Author: kripken

src/passes/DeadArgumentElimination.cpp

@@ -383,13 +383,14 @@ struct DAE : public Pass {
       while (1) {
         if (infoMap[name].unusedParams.has(i)) {
           // Great, it's not used. Check if none of the calls has a param with
-          // side effects, as that would prevent us removing them (flattening
-          // should have been done earlier).
+          // side effects that we cannot remove (as if we can remove them, we
+          // will simply do that when we remove the parameter). Note: flattening
+          // the IR beforehand can help here.
           bool callParamsAreValid =
             std::none_of(calls.begin(), calls.end(), [&](Call* call) {
               auto* operand = call->operands[i];
               return EffectAnalyzer(runner->options, *module, operand)
-                .hasSideEffects();
+                .hasUnremovableSideEffects();
             });
           // The type must be valid for us to handle as a local (since we
           // replace the parameter with a local).

test/lit/passes/dae_tnh.wast

@@ -0,0 +1,34 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py --all-items and should not be edited.
+
+;; RUN: foreach %s %t wasm-opt --dae --all-features -tnh -S -o - | filecheck %s
+
+(module
+  ;; CHECK:      (type $none_=>_none (func))
+
+  ;; CHECK:      (type $ref?|$struct|_=>_none (func (param (ref null $struct))))
+
+  ;; CHECK:      (type $struct (struct (field i32)))
+  (type $struct (struct_subtype (field i32) data))
+
+  ;; CHECK:      (func $target
+  ;; CHECK-NEXT:  (local $0 i32)
+  ;; CHECK-NEXT:  (nop)
+  ;; CHECK-NEXT: )
+  (func $target (param $x i32)
+    (nop)
+  )
+
+  ;; CHECK:      (func $caller (param $ref (ref null $struct))
+  ;; CHECK-NEXT:  (call $target)
+  ;; CHECK-NEXT: )
+  (func $caller (param $ref (ref null $struct))
+    (call $target
+      ;; This might trap in theory, but in traps-never-happen mode which is
+      ;; enabled here, we can ignore and remove such side effects, allowing us
+      ;; to optimize away this parameter which is never used.
+      (struct.get $struct 0
+        (local.get $ref)
+      )
+    )
+  )
+)