Fix trapping and dangling insts in memory packing (#2540)

This does two things:
- Restore `visitDataDrop` handler deleted in #2529, but now we convert
  invalid `data.drop`s to not `unreachable` but `nop`. This conforms to
  the revised spec that `data.drop` on the active segment can be treated
  as a nop.
- Make `visitMemoryInit` trap if offset or size are not equal to 0 or if
  the dest address is out of bounds. Otherwise drop all its argument.

Fixes #2535.

Author: aheejin

src/passes/MemoryPacking.cpp

@@ -135,10 +135,20 @@ struct MemoryPacking : public Pass {
       void visitMemoryInit(MemoryInit* curr) {
         if (!getModule()->memory.segments[curr->segment].isPassive) {
           Builder builder(*getModule());
-          replaceCurrent(builder.blockify(builder.makeDrop(curr->dest),
-                                          builder.makeDrop(curr->offset),
-                                          builder.makeDrop(curr->size),
-                                          builder.makeUnreachable()));
+          // trap if (dest > memory.size | offset | size) != 0
+          replaceCurrent(builder.makeIf(
+            builder.makeBinary(
+              OrInt32,
+              builder.makeBinary(
+                GtUInt32, curr->dest, builder.makeHost(MemorySize, Name(), {})),
+              builder.makeBinary(OrInt32, curr->offset, curr->size)),
+            builder.makeUnreachable()));
+          changed = true;
+        }
+      }
+      void visitDataDrop(DataDrop* curr) {
+        if (!getModule()->memory.segments[curr->segment].isPassive) {
+          ExpressionManipulator::nop(curr);
           changed = true;
         }
       }

test/passes/memory-packing_all-features.txt

@@ -22,15 +22,26 @@
  (type $none_=>_none (func))
  (memory $0 1 1)
  (func $foo (; 0 ;)
-  (drop
-   (i32.const 0)
-  )
-  (drop
-   (i32.const 0)
+  (if
+   (i32.or
+    (i32.gt_u
+     (i32.const 0)
+     (memory.size)
+    )
+    (i32.or
+     (i32.const 0)
+     (i32.const 0)
+    )
+   )
+   (unreachable)
   )
+ )
+ (func $bar (; 1 ;)
   (drop
-   (i32.const 0)
+   (loop $loop-in (result i32)
+    (nop)
+    (i32.const 42)
+   )
   )
-  (unreachable)
  )
 )

test/passes/memory-packing_all-features.wast

@@ -27,4 +27,12 @@
    (i32.const 0)
   )
  )
+ (func $bar
+  (drop
+   (loop (result i32)
+    (data.drop 0)
+    (i32.const 42)
+   )
+  )
+ )
 )