4 files changed, 51 insertions, 8 deletions
diff --git a/src/ir/effects.h b/src/ir/effects.h
index f6c87a4e5..9d6e90936 100644
--- a/src/ir/effects.h
+++ b/src/ir/effects.h
@@ -392,8 +392,10 @@ struct EffectAnalyzer
     }
   }
   void visitDataDrop(DataDrop* curr) {
-    // prevent reordering with memory.init
-    readsMemory = true;
+    // data.drop does not actually write memory, but it does alter the size of
+    // a segment, which can be noticeable later by memory.init, so we need to
+    // mark it as having a global side effect of some kind.
+    writesMemory = true;
     if (!ignoreImplicitTraps) {
       implicitTrap = true;
     }
diff --git a/test/passes/simplify-locals_all-features.txt b/test/passes/simplify-locals_all-features.txt
index fbb1f87ed..34efb8726 100644
--- a/test/passes/simplify-locals_all-features.txt
+++ b/test/passes/simplify-locals_all-features.txt
@@ -1837,13 +1837,15 @@
  )
  (func $data-drop-load
   (local $x i32)
-  (nop)
-  (data.drop 0)
-  (drop
+  (local.set $x
    (i32.load
     (i32.const 0)
    )
   )
+  (data.drop 0)
+  (drop
+   (local.get $x)
+  )
  )
  (func $data-drop-store
   (local $x i32)
@@ -2019,3 +2021,22 @@
   )
  )
 )
+(module
+ (type $none_=>_i32 (func (result i32)))
+ (memory $0 (shared 1 1))
+ (data passive "data")
+ (export "foo" (func $0))
+ (func $0 (result i32)
+  (local $0 i32)
+  (block $block (result i32)
+   (local.set $0
+    (i32.rem_u
+     (i32.const 0)
+     (i32.const 0)
+    )
+   )
+   (data.drop 0)
+   (local.get $0)
+  )
+ )
+)
diff --git a/test/passes/simplify-locals_all-features.wast b/test/passes/simplify-locals_all-features.wast
index a8e1a161f..3edffca7e 100644
--- a/test/passes/simplify-locals_all-features.wast
+++ b/test/passes/simplify-locals_all-features.wast
@@ -1782,3 +1782,21 @@
     )
   )
 )
+;; data.drop has global side effects
+(module
+ (memory $0 (shared 1 1))
+ (data passive "data")
+ (func "foo" (result i32)
+  (local $0 i32)
+  (block (result i32)
+   (local.set $0
+    (i32.rem_u     ;; will trap, so cannot be reordered to the end
+     (i32.const 0)
+     (i32.const 0)
+    )
+   )
+   (data.drop 0)   ;; has global side effects that may be noticed later
+   (local.get $0)
+  )
+ )
+)
diff --git a/test/passes/simplify-locals_all-features_disable-exception-handling.txt b/test/passes/simplify-locals_all-features_disable-exception-handling.txt
index 7be68af6d..0d035234b 100644
--- a/test/passes/simplify-locals_all-features_disable-exception-handling.txt
+++ b/test/passes/simplify-locals_all-features_disable-exception-handling.txt
@@ -1831,13 +1831,15 @@
  )
  (func $data-drop-load
   (local $x i32)
-  (nop)
-  (data.drop 0)
-  (drop
+  (local.set $x
    (i32.load
     (i32.const 0)
    )
   )
+  (data.drop 0)
+  (drop
+   (local.get $x)
+  )
  )
  (func $data-drop-store
   (local $x i32)