Fix the effects of array.copy (#4118)

This appeared to be a regression from #4117, however this
was always a bug, and that PR just exposed it. That is,
somehow we forgot to indicate the effects of ArrayCopy, and
after that PR we'd vacuum it out incorrectly.

2 files changed, 16 insertions, 0 deletions

diff --git a/src/ir/effects.h b/src/ir/effects.h
index b9393ade2..475e6f2b1 100644
--- a/src/ir/effects.h
+++ b/src/ir/effects.h
@@ -659,6 +659,8 @@ private:
       }
     }
     void visitArrayCopy(ArrayCopy* curr) {
+      parent.readsArray = true;
+      parent.writesArray = true;
       // traps when a ref is null, or when out of bounds.
       parent.implicitTrap = true;
     }
diff --git a/test/example/cpp-unit.cpp b/test/example/cpp-unit.cpp
index 9c95bb31c..41096a43a 100644
--- a/test/example/cpp-unit.cpp
+++ b/test/example/cpp-unit.cpp
@@ -599,12 +599,26 @@ void test_cost() {
 void test_effects() {
   PassOptions options;
   Module module;
+
   // Unreachables trap.
   Unreachable unreachable;
   assert_equal(EffectAnalyzer(options, module, &unreachable).trap, true);
+
   // Nops... do not.
   Nop nop;
   assert_equal(EffectAnalyzer(options, module, &nop).trap, false);
+
+  // ArrayCopy can trap, reads arrays, and writes arrays (but not structs).
+  {
+    ArrayCopy arrayCopy(module.allocator);
+    EffectAnalyzer effects(options, module);
+    effects.visit(&arrayCopy);
+    assert_equal(effects.trap, true);
+    assert_equal(effects.readsArray, true);
+    assert_equal(effects.writesArray, true);
+    assert_equal(effects.readsStruct, false);
+    assert_equal(effects.writesStruct, false);
+  }
 }
 
 void test_literals() {