EffectAnalyzer: Do not clear break targets before walk()/visit() (#5723)

We depend on repeated calls to walk/visit accumulating effects, so this
was a bug; if we want to clear stuff then we create a new EffectAnalyzer.

Removing that fixes the attached testcase. Also added a unit test.

1 files changed, 13 insertions, 0 deletions

diff --git a/test/example/cpp-unit.cpp b/test/example/cpp-unit.cpp
index d2339f030..e3e1269c3 100644
--- a/test/example/cpp-unit.cpp
+++ b/test/example/cpp-unit.cpp
@@ -637,6 +637,19 @@ void test_effects() {
     assert_equal(effects.readsMutableStruct, false);
     assert_equal(effects.writesStruct, false);
   }
+
+  {
+    EffectAnalyzer effects(options, module);
+
+    // If we break, then we transfer control flow.
+    effects.breakTargets.insert("block");
+    assert_equal(effects.transfersControlFlow(), true);
+
+    // Repeated walks accumulate effects, that is, old effects are not
+    // removed.
+    effects.walk(&nop);
+    assert_equal(effects.transfersControlFlow(), true);
+  }
 }
 
 void test_field() {