Remove optimization for memory.copy(x, x, C) (#3073)

That can trap, so we can only remove it if traps are ignored,
which was not handled properly. Revert it as we consider the
options.

Author: MaxGraey

src/passes/OptimizeInstructions.cpp

@@ -1399,16 +1399,6 @@ struct OptimizeInstructions
   }
 
   Expression* optimizeMemoryCopy(MemoryCopy* memCopy) {
-    FeatureSet features = getModule()->features;
-
-    // memory.copy(x, x, sz)  ==>  nop
-    if (!EffectAnalyzer(getPassOptions(), features, memCopy->dest)
-           .hasSideEffects() &&
-        !EffectAnalyzer(getPassOptions(), features, memCopy->size)
-           .hasSideEffects() &&
-        ExpressionAnalyzer::equal(memCopy->dest, memCopy->source)) {
-      return ExpressionManipulator::nop(memCopy);
-    }
     // memory.copy(dst, src, C)  ==>  store(dst, load(src))
     if (auto* csize = memCopy->size->dynCast<Const>()) {
       auto bytes = csize->value.geti32();
@@ -1444,7 +1434,7 @@ struct OptimizeInstructions
           if (getPassOptions().shrinkLevel == 0) {
             // This adds an extra 2 bytes so apply it only for
             // minimal shrink level
-            if (features.hasSIMD()) {
+            if (getModule()->features.hasSIMD()) {
               return builder.makeStore(
                 bytes, // bytes
                 0,     // offset

test/passes/optimize-instructions_all-features.txt

@@ -3729,7 +3729,11 @@
   )
  )
  (func $optimize-bulk-memory-copy (param $dst i32) (param $src i32) (param $sz i32)
-  (nop)
+  (memory.copy
+   (local.get $dst)
+   (local.get $dst)
+   (local.get $sz)
+  )
   (block
    (drop
     (local.get $dst)

test/passes/optimize-instructions_all-features.wast

@@ -4234,7 +4234,7 @@
     ))
   )
   (func $optimize-bulk-memory-copy (param $dst i32) (param $src i32) (param $sz i32)
-    (memory.copy  ;; nop
+    (memory.copy  ;; skip
       (local.get $dst)
       (local.get $dst)
       (local.get $sz)