[StackSwitching] CFG: Fix basic blocks around Resume

src/cfg/cfg-traversal.h

@@ -452,11 +452,13 @@ struct CFGWalker : public PostWalker<SubType, VisitorType> {
     }
     auto handlerBlocks = BranchUtils::getUniqueTargets(*currp);
     // Add branches to the targets.
+    auto* last = self->currBasicBlock;
     for (auto target : handlerBlocks) {
       if (target) {
-        self->branches[target].push_back(self->currBasicBlock);
+        self->branches[target].push_back(last);
       }
     }
+    self->link(last, self->startBasicBlock()); // we might fall through
   }
 
   static bool isReturnCall(Expression* curr) {

src/passes/ConstraintAnalysis.cpp

@@ -57,8 +57,11 @@ struct Info {
   BasicBlockConstraintMap startConstraints;
 
   void dump(Function* func) {
-    std::cout << "Info{" << actions.size() << ", " << brancher << ", "
-              << startConstraints << "}\n";
+    std::cout << "Info{" << actions.size();
+    if (brancher) {
+      std::cout << ", " << *brancher;
+    }
+    std::cout << ", " << startConstraints << "}\n";
   }
 };
 

test/lit/passes/constraint-analysis-cont.wast

@@ -0,0 +1,76 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.
+
+;; RUN: wasm-opt %s --constraint-analysis -all -S -o - | filecheck %s
+
+(module
+ ;; CHECK:      (type $func (func))
+ (type $func (func))
+ ;; CHECK:      (type $cont (cont $func))
+ (type $cont (cont $func))
+
+ ;; CHECK:      (tag $tag (type $func))
+ (tag $tag (type $func))
+
+ ;; CHECK:      (func $func (type $2) (param $cont (ref $cont))
+ ;; CHECK-NEXT:  (local $x i32)
+ ;; CHECK-NEXT:  (block $out
+ ;; CHECK-NEXT:   (drop
+ ;; CHECK-NEXT:    (block $in (result (ref $cont))
+ ;; CHECK-NEXT:     (resume $cont (on $tag $in)
+ ;; CHECK-NEXT:      (local.get $cont)
+ ;; CHECK-NEXT:     )
+ ;; CHECK-NEXT:     (local.set $x
+ ;; CHECK-NEXT:      (i32.const 1)
+ ;; CHECK-NEXT:     )
+ ;; CHECK-NEXT:     (br $out)
+ ;; CHECK-NEXT:    )
+ ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT:  (drop
+ ;; CHECK-NEXT:   (i32.eq
+ ;; CHECK-NEXT:    (local.get $x)
+ ;; CHECK-NEXT:    (i32.const 0)
+ ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT:  (drop
+ ;; CHECK-NEXT:   (i32.eq
+ ;; CHECK-NEXT:    (local.get $x)
+ ;; CHECK-NEXT:    (i32.const 1)
+ ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT: )
+ (func $func (param $cont (ref $cont))
+  (local $x i32)
+
+  (block $out
+   (drop
+    (block $in (result (ref $cont))
+     (resume $cont (on $tag $in)
+      (local.get $cont)
+     )
+     ;; This might or might not be reached, depending on if the resume branches
+     ;; to $in.
+     (local.set $x
+      (i32.const 1)
+     )
+     (br $out)
+    )
+   )
+  )
+
+  ;; We cannot be sure if x is 0 or 1, so nothing is optimized here.
+  (drop
+   (i32.eq
+    (local.get $x)
+    (i32.const 0)
+   )
+  )
+  (drop
+   (i32.eq
+    (local.get $x)
+    (i32.const 1)
+   )
+  )
+ )
+)
+