Bysyncify: fix skipping of flattened if condition (#2187)

We assigned it to a local, but didn't run maybeSkip on it. As a result, it was executed during rewinding, which broke restoring the saved value.

Found by the fuzzer.

Author: kripken

src/passes/Bysyncify.cpp

@@ -658,7 +658,10 @@ struct BysyncifyFlow : public Pass {
         return iff;
       }
       auto conditionTemp = builder->addVar(func, i32);
-      iff->condition = builder->makeLocalTee(conditionTemp, iff->condition);
+      // TODO: can avoid pre if the condition is a get or a const
+      auto* pre =
+        makeMaybeSkip(builder->makeLocalSet(conditionTemp, iff->condition));
+      iff->condition = builder->makeLocalGet(conditionTemp, i32);
       iff->condition = builder->makeBinary(
         OrInt32, iff->condition, builder->makeStateCheck(State::Rewinding));
       iff->ifTrue = process(iff->ifTrue);
@@ -674,7 +677,7 @@ struct BysyncifyFlow : public Pass {
           builder->makeStateCheck(State::Rewinding)),
         process(otherArm));
       otherIf->finalize();
-      return builder->makeSequence(iff, otherIf);
+      return builder->makeBlock({pre, iff, otherIf});
     } else if (auto* loop = curr->dynCast<Loop>()) {
       loop->body = process(loop->body);
       return loop;

test/passes/bysyncify.txt

@@ -1365,11 +1365,18 @@
          )
         )
         (block
+         (if
+          (i32.eq
+           (global.get $__bysyncify_state)
+           (i32.const 0)
+          )
+          (local.set $2
+           (local.get $1)
+          )
+         )
          (if
           (i32.or
-           (local.tee $2
-            (local.get $1)
-           )
+           (local.get $2)
            (i32.eq
             (global.get $__bysyncify_state)
             (i32.const 2)
@@ -1616,11 +1623,18 @@
          )
         )
         (block
+         (if
+          (i32.eq
+           (global.get $__bysyncify_state)
+           (i32.const 0)
+          )
+          (local.set $4
+           (local.get $1)
+          )
+         )
          (if
           (i32.or
-           (local.tee $4
-            (local.get $1)
-           )
+           (local.get $4)
            (i32.eq
             (global.get $__bysyncify_state)
             (i32.const 2)
@@ -1856,11 +1870,18 @@
          )
         )
         (block
+         (if
+          (i32.eq
+           (global.get $__bysyncify_state)
+           (i32.const 0)
+          )
+          (local.set $4
+           (local.get $1)
+          )
+         )
          (if
           (i32.or
-           (local.tee $4
-            (local.get $1)
-           )
+           (local.get $4)
            (i32.eq
             (global.get $__bysyncify_state)
             (i32.const 2)