Switch optimizations in remove-unused-brs (#1753)

* Switch optimizations in remove-unused-brs: thread switch jumps, and turn a switch with all identical targets into a br

* refinalize in interm operations in remove-unused-brs, as we can be confused by it

13 files changed, 307 insertions, 172 deletions

diff --git a/src/ir/branch-utils.h b/src/ir/branch-utils.h
index 84be9f897..6f9299bf5 100644
--- a/src/ir/branch-utils.h
+++ b/src/ir/branch-utils.h
@@ -45,6 +45,40 @@ inline bool isBranchReachable(Expression* expr) {
   WASM_UNREACHABLE();
 }
 
+inline std::set<Name> getUniqueTargets(Switch* sw) {
+  std::set<Name> ret;
+  for (auto target : sw->targets) {
+    ret.insert(target);
+  }
+  ret.insert(sw->default_);
+  return ret;
+}
+
+// If we branch to 'from', change that to 'to' instead.
+inline bool replacePossibleTarget(Expression* branch, Name from, Name to) {
+  bool worked = false;
+  if (auto* br = branch->dynCast<Break>()) {
+    if (br->name == from) {
+      br->name = to;
+      worked = true;
+    }
+  } else if (auto* sw = branch->dynCast<Switch>()) {
+    for (auto& target : sw->targets) {
+      if (target == from) {
+        target = to;
+        worked = true;
+      }
+    }
+    if (sw->default_ == from) {
+      sw->default_ = to;
+      worked = true;
+    }
+  } else {
+    WASM_UNREACHABLE();
+  }
+  return worked;
+}
+
 // returns the set of targets to which we branch that are
 // outside of a node
 inline std::set<Name> getExitingBranches(Expression* ast) {
diff --git a/src/passes/Flatten.cpp b/src/passes/Flatten.cpp
index f4b468098..aa5c1a491 100644
--- a/src/passes/Flatten.cpp
+++ b/src/passes/Flatten.cpp
@@ -53,8 +53,9 @@
 #include <wasm.h>
 #include <pass.h>
 #include <wasm-builder.h>
-#include <ir/utils.h>
+#include <ir/branch-utils.h>
 #include <ir/effects.h>
+#include <ir/utils.h>
 
 namespace wasm {
 
@@ -232,11 +233,7 @@ struct Flatten : public WalkerPass<ExpressionStackWalker<Flatten, UnifiedExpress
             Index temp = builder.addVar(getFunction(), type);
             ourPreludes.push_back(builder.makeSetLocal(temp, sw->value));
             // we don't know which break target will be hit - assign to them all
-            std::set<Name> names;
-            for (auto target : sw->targets) {
-              names.insert(target);
-            }
-            names.insert(sw->default_);
+            auto names = BranchUtils::getUniqueTargets(sw);
             for (auto name : names) {
               ourPreludes.push_back(builder.makeSetLocal(
                 getTempForBreakTarget(name, type),
diff --git a/src/passes/RemoveUnusedBrs.cpp b/src/passes/RemoveUnusedBrs.cpp
index eb81b0a5a..62ecb3ed3 100644
--- a/src/passes/RemoveUnusedBrs.cpp
+++ b/src/passes/RemoveUnusedBrs.cpp
@@ -435,7 +435,7 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs>> {
     }
   }
 
-  void sinkBlocks(Function* func) {
+  bool sinkBlocks(Function* func) {
     struct Sinker : public PostWalker<Sinker> {
       bool worked = false;
 
@@ -501,13 +501,14 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs>> {
 
     sinker.doWalkFunction(func);
     if (sinker.worked) {
-      anotherCycle = true;
+      ReFinalize().walkFunctionInModule(func, getModule());
+      return true;
     }
+    return false;
   }
 
   void doWalkFunction(Function* func) {
     // multiple cycles may be needed
-    bool worked = false;
     do {
       anotherCycle = false;
       super::doWalkFunction(func);
@@ -532,32 +533,39 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs>> {
         anotherCycle |= optimizeLoop(loop);
       }
       loops.clear();
+      if (anotherCycle) {
+        ReFinalize().walkFunctionInModule(func, getModule());
+      }
       // sink blocks
-      sinkBlocks(func);
-      if (anotherCycle) worked = true;
+      if (sinkBlocks(func)) {
+        anotherCycle = true;
+      }
     } while (anotherCycle);
 
-    if (worked) {
-      // Our work may alter block and if types, they may now return values that we made flow through them
-      ReFinalize().walkFunctionInModule(func, getModule());
-    }
-
     // thread trivial jumps
     struct JumpThreader : public ControlFlowWalker<JumpThreader> {
-      // map of all value-less breaks going to a block (and not a loop)
-      std::map<Block*, std::vector<Break*>> breaksToBlock;
+      // map of all value-less breaks and switches going to a block (and not a loop)
+      std::map<Block*, std::vector<Expression*>> branchesToBlock;
 
-      // the names to update
-      std::map<Break*, Name> newNames;
+      bool worked = false;
 
       void visitBreak(Break* curr) {
         if (!curr->value) {
           if (auto* target = findBreakTarget(curr->name)->dynCast<Block>()) {
-            breaksToBlock[target].push_back(curr);
+            branchesToBlock[target].push_back(curr);
+          }
+        }
+      }
+      void visitSwitch(Switch* curr) {
+        if (!curr->value) {
+          auto names = BranchUtils::getUniqueTargets(curr);
+          for (auto name : names) {
+            if (auto* target = findBreakTarget(name)->dynCast<Block>()) {
+              branchesToBlock[target].push_back(curr);
+            }
           }
         }
       }
-      // TODO: Switch?
       void visitBlock(Block* curr) {
         auto& list = curr->list;
         if (list.size() == 1 && curr->name.is()) {
@@ -566,12 +574,7 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs>> {
             // the two blocks must have the same type for us to update the branch, as otherwise
             // one block may be unreachable and the other concrete, so one might lack a value
             if (child->name.is() && child->name != curr->name && child->type == curr->type) {
-              auto& breaks = breaksToBlock[child];
-              for (auto* br : breaks) {
-                newNames[br] = curr->name;
-                breaksToBlock[curr].push_back(br); // update the list - we may push it even more later
-              }
-              breaksToBlock.erase(child);
+              redirectBranches(child, curr->name);
             }
           }
         } else if (list.size() == 2) {
@@ -579,28 +582,28 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs>> {
           auto* child = list[0]->dynCast<Block>();
           auto* jump = list[1]->dynCast<Break>();
           if (child && child->name.is() && jump && ExpressionAnalyzer::isSimple(jump)) {
-            auto& breaks = breaksToBlock[child];
-            for (auto* br : breaks) {
-              newNames[br] = jump->name;
-            }
-            // if the jump is to another block then we can update the list, and maybe push it even more later
-            if (auto* newTarget = findBreakTarget(jump->name)->dynCast<Block>()) {
-              for (auto* br : breaks) {
-                breaksToBlock[newTarget].push_back(br);
-              }
-            }
-            breaksToBlock.erase(child);
+            redirectBranches(child, jump->name);
           }
         }
       }
 
-      void finish(Function* func) {
-        for (auto& iter : newNames) {
-          auto* br = iter.first;
-          auto name = iter.second;
-          br->name = name;
+      void redirectBranches(Block* from, Name to) {
+        auto& branches = branchesToBlock[from];
+        for (auto* branch : branches) {
+          if (BranchUtils::replacePossibleTarget(branch, from->name, to)) {
+            worked = true;
+          }
+        }
+        // if the jump is to another block then we can update the list, and maybe push it even more later
+        if (auto* newTarget = findBreakTarget(to)->dynCast<Block>()) {
+          for (auto* branch : branches) {
+            branchesToBlock[newTarget].push_back(branch);
+          }
         }
-        if (newNames.size() > 0) {
+      }
+
+      void finish(Function* func) {
+        if (worked) {
           // by changing where brs go, we may change block types etc.
           ReFinalize().walkFunctionInModule(func, getModule());
         }
@@ -686,6 +689,19 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs>> {
         }
       }
 
+      void visitSwitch(Switch* curr) {
+        if (BranchUtils::getUniqueTargets(curr).size() == 1) {
+          // This switch has just one target no matter what; replace with a br.
+          Builder builder(*getModule());
+          replaceCurrent(
+            builder.makeSequence(
+              builder.makeDrop(curr->condition), // might have side effects
+              builder.makeBreak(curr->default_, curr->value)
+            )
+          );
+        }
+      }
+
       // Restructuring of ifs: if we have
       //   (block $x
       //     (br_if $x (cond))
diff --git a/src/passes/SimplifyLocals.cpp b/src/passes/SimplifyLocals.cpp
index aadf766ac..bf4eed24e 100644
--- a/src/passes/SimplifyLocals.cpp
+++ b/src/passes/SimplifyLocals.cpp
@@ -50,6 +50,7 @@
 #include <wasm-builder.h>
 #include <wasm-traversal.h>
 #include <pass.h>
+#include <ir/branch-utils.h>
 #include <ir/count.h>
 #include <ir/effects.h>
 #include "ir/equivalent_sets.h"
@@ -128,10 +129,10 @@ struct SimplifyLocals : public WalkerPass<LinearExecutionWalker<SimplifyLocals<a
       assert(!curr->cast<If>()->ifFalse); // if-elses are handled by doNoteIfElse* methods
     } else if (curr->is<Switch>()) {
       auto* sw = curr->cast<Switch>();
-      for (auto target : sw->targets) {
+      auto targets = BranchUtils::getUniqueTargets(sw);
+      for (auto target : targets) {
         self->unoptimizableBlocks.insert(target);
       }
-      self->unoptimizableBlocks.insert(sw->default_);
       // TODO: we could use this info to stop gathering data on these blocks
     }
     self->sinkables.clear();
diff --git a/test/emcc_hello_world.fromasm b/test/emcc_hello_world.fromasm
index cb9b99b74..e70998db0 100644
--- a/test/emcc_hello_world.fromasm
+++ b/test/emcc_hello_world.fromasm
@@ -3309,19 +3309,19 @@
              (block $__rjti$4
               (block $__rjti$3
                (block $switch-default120
-                (block $switch-case42
+                (block $switch-case119
                  (block $switch-case41
                   (block $switch-case40
                    (block $switch-case39
                     (block $switch-case38
                      (block $switch-case37
                       (block $switch-case36
-                       (block $switch-case34
+                       (block $switch-case35
                         (block $switch-case33
-                         (block $switch-case29
+                         (block $switch-case30
                           (block $switch-case28
                            (block $switch-case27
-                            (br_table $switch-case42 $switch-default120 $switch-case40 $switch-default120 $switch-case42 $switch-case42 $switch-case42 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-case41 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-case29 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-case42 $switch-default120 $switch-case37 $switch-case34 $switch-case42 $switch-case42 $switch-case42 $switch-default120 $switch-case34 $switch-default120 $switch-default120 $switch-default120 $switch-case38 $switch-case27 $switch-case33 $switch-case28 $switch-default120 $switch-default120 $switch-case39 $switch-default120 $switch-case36 $switch-default120 $switch-default120 $switch-case29 $switch-default120
+                            (br_table $switch-case119 $switch-default120 $switch-case40 $switch-default120 $switch-case119 $switch-case119 $switch-case119 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-case41 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-case30 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-case119 $switch-default120 $switch-case37 $switch-case35 $switch-case119 $switch-case119 $switch-case119 $switch-default120 $switch-case35 $switch-default120 $switch-default120 $switch-default120 $switch-case38 $switch-case27 $switch-case33 $switch-case28 $switch-default120 $switch-default120 $switch-case39 $switch-default120 $switch-case36 $switch-default120 $switch-default120 $switch-case30 $switch-default120
                              (i32.sub
                               (tee_local $19
                                (select
@@ -6915,7 +6915,7 @@
     (get_local $1)
     (i32.const 20)
    )
-   (block $switch-default
+   (block $label$break$L1
     (block $switch-case9
      (block $switch-case8
       (block $switch-case7
@@ -6926,7 +6926,7 @@
            (block $switch-case2
             (block $switch-case1
              (block $switch-case
-              (br_table $switch-case $switch-case1 $switch-case2 $switch-case3 $switch-case4 $switch-case5 $switch-case6 $switch-case7 $switch-case8 $switch-case9 $switch-default
+              (br_table $switch-case $switch-case1 $switch-case2 $switch-case3 $switch-case4 $switch-case5 $switch-case6 $switch-case7 $switch-case8 $switch-case9 $label$break$L1
                (i32.sub
                 (get_local $1)
                 (i32.const 9)
@@ -6959,7 +6959,7 @@
               (get_local $0)
               (get_local $3)
              )
-             (br $switch-default)
+             (br $label$break$L1)
             )
             (set_local $1
              (i32.load
@@ -7000,7 +7000,7 @@
               (i32.const 31)
              )
             )
-            (br $switch-default)
+            (br $label$break$L1)
            )
            (set_local $3
             (i32.load
@@ -7032,7 +7032,7 @@
             (get_local $0)
             (i32.const 0)
            )
-           (br $switch-default)
+           (br $label$break$L1)
           )
           (set_local $5
            (i32.load
@@ -7071,7 +7071,7 @@
            (get_local $0)
            (get_local $3)
           )
-          (br $switch-default)
+          (br $label$break$L1)
          )
          (set_local $3
           (i32.load
@@ -7123,7 +7123,7 @@
            (i32.const 31)
           )
          )
-         (br $switch-default)
+         (br $label$break$L1)
         )
         (set_local $3
          (i32.load
@@ -7158,7 +7158,7 @@
          (get_local $0)
          (i32.const 0)
         )
-        (br $switch-default)
+        (br $label$break$L1)
        )
        (set_local $3
         (i32.load
@@ -7210,7 +7210,7 @@
          (i32.const 31)
         )
        )
-       (br $switch-default)
+       (br $label$break$L1)
       )
       (set_local $3
        (i32.load
@@ -7245,7 +7245,7 @@
        (get_local $0)
        (i32.const 0)
       )
-      (br $switch-default)
+      (br $label$break$L1)
      )
      (set_local $4
       (f64.load
@@ -7273,7 +7273,7 @@
       (get_local $0)
       (get_local $4)
      )
-     (br $switch-default)
+     (br $label$break$L1)
     )
     (set_local $4
      (f64.load
diff --git a/test/emcc_hello_world.fromasm.clamp b/test/emcc_hello_world.fromasm.clamp
index dafa2db7b..244f8adba 100644
--- a/test/emcc_hello_world.fromasm.clamp
+++ b/test/emcc_hello_world.fromasm.clamp
@@ -3359,19 +3359,19 @@
              (block $__rjti$4
               (block $__rjti$3
                (block $switch-default120
-                (block $switch-case42
+                (block $switch-case119
                  (block $switch-case41
                   (block $switch-case40
                    (block $switch-case39
                     (block $switch-case38
                      (block $switch-case37
                       (block $switch-case36
-                       (block $switch-case34
+                       (block $switch-case35
                         (block $switch-case33
-                         (block $switch-case29
+                         (block $switch-case30
                           (block $switch-case28
                            (block $switch-case27
-                            (br_table $switch-case42 $switch-default120 $switch-case40 $switch-default120 $switch-case42 $switch-case42 $switch-case42 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-case41 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-case29 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-case42 $switch-default120 $switch-case37 $switch-case34 $switch-case42 $switch-case42 $switch-case42 $switch-default120 $switch-case34 $switch-default120 $switch-default120 $switch-default120 $switch-case38 $switch-case27 $switch-case33 $switch-case28 $switch-default120 $switch-default120 $switch-case39 $switch-default120 $switch-case36 $switch-default120 $switch-default120 $switch-case29 $switch-default120
+                            (br_table $switch-case119 $switch-default120 $switch-case40 $switch-default120 $switch-case119 $switch-case119 $switch-case119 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-case41 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-case30 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-case119 $switch-default120 $switch-case37 $switch-case35 $switch-case119 $switch-case119 $switch-case119 $switch-default120 $switch-case35 $switch-default120 $switch-default120 $switch-default120 $switch-case38 $switch-case27 $switch-case33 $switch-case28 $switch-default120 $switch-default120 $switch-case39 $switch-default120 $switch-case36 $switch-default120 $switch-default120 $switch-case30 $switch-default120
                              (i32.sub
                               (tee_local $19
                                (select
@@ -6965,7 +6965,7 @@
     (get_local $1)
     (i32.const 20)
    )
-   (block $switch-default
+   (block $label$break$L1
     (block $switch-case9
      (block $switch-case8
       (block $switch-case7
@@ -6976,7 +6976,7 @@
            (block $switch-case2
             (block $switch-case1
              (block $switch-case
-              (br_table $switch-case $switch-case1 $switch-case2 $switch-case3 $switch-case4 $switch-case5 $switch-case6 $switch-case7 $switch-case8 $switch-case9 $switch-default
+              (br_table $switch-case $switch-case1 $switch-case2 $switch-case3 $switch-case4 $switch-case5 $switch-case6 $switch-case7 $switch-case8 $switch-case9 $label$break$L1
                (i32.sub
                 (get_local $1)
                 (i32.const 9)
@@ -7009,7 +7009,7 @@
               (get_local $0)
               (get_local $3)
              )
-             (br $switch-default)
+             (br $label$break$L1)
             )
             (set_local $1
              (i32.load
@@ -7050,7 +7050,7 @@
               (i32.const 31)
              )
             )
-            (br $switch-default)
+            (br $label$break$L1)
            )
            (set_local $3
             (i32.load
@@ -7082,7 +7082,7 @@
             (get_local $0)
             (i32.const 0)
            )
-           (br $switch-default)
+           (br $label$break$L1)
           )
           (set_local $5
            (i32.load
@@ -7121,7 +7121,7 @@
            (get_local $0)
            (get_local $3)
           )
-          (br $switch-default)
+          (br $label$break$L1)
          )
          (set_local $3
           (i32.load
@@ -7173,7 +7173,7 @@
            (i32.const 31)
           )
          )
-         (br $switch-default)
+         (br $label$break$L1)
         )
         (set_local $3
          (i32.load
@@ -7208,7 +7208,7 @@
          (get_local $0)
          (i32.const 0)
         )
-        (br $switch-default)
+        (br $label$break$L1)
        )
        (set_local $3
         (i32.load
@@ -7260,7 +7260,7 @@
          (i32.const 31)
         )
        )
-       (br $switch-default)
+       (br $label$break$L1)
       )
       (set_local $3
        (i32.load
@@ -7295,7 +7295,7 @@
        (get_local $0)
        (i32.const 0)
       )
-      (br $switch-default)
+      (br $label$break$L1)
      )
      (set_local $4
       (f64.load
@@ -7323,7 +7323,7 @@
       (get_local $0)
       (get_local $4)
      )
-     (br $switch-default)
+     (br $label$break$L1)
     )
     (set_local $4
      (f64.load
diff --git a/test/emcc_hello_world.fromasm.imprecise b/test/emcc_hello_world.fromasm.imprecise
index ed05f6905..5cfa87fe1 100644
--- a/test/emcc_hello_world.fromasm.imprecise
+++ b/test/emcc_hello_world.fromasm.imprecise
@@ -3249,19 +3249,19 @@
              (block $__rjti$4
               (block $__rjti$3
                (block $switch-default120
-                (block $switch-case42
+                (block $switch-case119
                  (block $switch-case41
                   (block $switch-case40
                    (block $switch-case39
                     (block $switch-case38
                      (block $switch-case37
                       (block $switch-case36
-                       (block $switch-case34
+                       (block $switch-case35
                         (block $switch-case33
-                         (block $switch-case29
+                         (block $switch-case30
                           (block $switch-case28
                            (block $switch-case27
-                            (br_table $switch-case42 $switch-default120 $switch-case40 $switch-default120 $switch-case42 $switch-case42 $switch-case42 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-case41 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-case29 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-case42 $switch-default120 $switch-case37 $switch-case34 $switch-case42 $switch-case42 $switch-case42 $switch-default120 $switch-case34 $switch-default120 $switch-default120 $switch-default120 $switch-case38 $switch-case27 $switch-case33 $switch-case28 $switch-default120 $switch-default120 $switch-case39 $switch-default120 $switch-case36 $switch-default120 $switch-default120 $switch-case29 $switch-default120
+                            (br_table $switch-case119 $switch-default120 $switch-case40 $switch-default120 $switch-case119 $switch-case119 $switch-case119 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-case41 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-case30 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-default120 $switch-case119 $switch-default120 $switch-case37 $switch-case35 $switch-case119 $switch-case119 $switch-case119 $switch-default120 $switch-case35 $switch-default120 $switch-default120 $switch-default120 $switch-case38 $switch-case27 $switch-case33 $switch-case28 $switch-default120 $switch-default120 $switch-case39 $switch-default120 $switch-case36 $switch-default120 $switch-default120 $switch-case30 $switch-default120
                              (i32.sub
                               (tee_local $19
                                (select
@@ -6829,7 +6829,7 @@
     (get_local $1)
     (i32.const 20)
    )
-   (block $switch-default
+   (block $label$break$L1
     (block $switch-case9
      (block $switch-case8
       (block $switch-case7
@@ -6840,7 +6840,7 @@
            (block $switch-case2
             (block $switch-case1
              (block $switch-case
-              (br_table $switch-case $switch-case1 $switch-case2 $switch-case3 $switch-case4 $switch-case5 $switch-case6 $switch-case7 $switch-case8 $switch-case9 $switch-default
+              (br_table $switch-case $switch-case1 $switch-case2 $switch-case3 $switch-case4 $switch-case5 $switch-case6 $switch-case7 $switch-case8 $switch-case9 $label$break$L1
                (i32.sub
                 (get_local $1)
                 (i32.const 9)
@@ -6873,7 +6873,7 @@
               (get_local $0)
               (get_local $3)
              )
-             (br $switch-default)
+             (br $label$break$L1)
             )
             (set_local $1
              (i32.load
@@ -6914,7 +6914,7 @@
               (i32.const 31)
              )
             )
-            (br $switch-default)
+            (br $label$break$L1)
            )
            (set_local $3
             (i32.load
@@ -6946,7 +6946,7 @@
             (get_local $0)
             (i32.const 0)
            )
-           (br $switch-default)
+           (br $label$break$L1)
           )
           (set_local $5
            (i32.load
@@ -6985,7 +6985,7 @@
            (get_local $0)
            (get_local $3)
           )
-          (br $switch-default)
+          (br $label$break$L1)
          )
          (set_local $3
           (i32.load
@@ -7037,7 +7037,7 @@
            (i32.const 31)
           )
          )
-         (br $switch-default)
+         (br $label$break$L1)
         )
         (set_local $3
          (i32.load
@@ -7072,7 +7072,7 @@
          (get_local $0)
          (i32.const 0)
         )
-        (br $switch-default)
+        (br $label$break$L1)
        )
        (set_local $3
         (i32.load
@@ -7124,7 +7124,7 @@
          (i32.const 31)
         )
        )
-       (br $switch-default)
+       (br $label$break$L1)
       )
       (set_local $3
        (i32.load
@@ -7159,7 +7159,7 @@
        (get_local $0)
        (i32.const 0)
       )
-      (br $switch-default)
+      (br $label$break$L1)
      )
      (set_local $4
       (f64.load
@@ -7187,7 +7187,7 @@
       (get_local $0)
       (get_local $4)
      )
-     (br $switch-default)
+     (br $label$break$L1)
     )
     (set_local $4
      (f64.load
diff --git a/test/passes/1.txt b/test/passes/1.txt
index 22b7032fe..cf6a569eb 100644
--- a/test/passes/1.txt
+++ b/test/passes/1.txt
@@ -196,12 +196,9 @@
     (i32.const 1)
    )
    (block $switch$3$default
-    (block $switch$3$case$6
-     (br_table $switch$3$case$6 $switch$3$case$6 $switch$3$case$6 $switch$3$default
-      (get_local $0)
-     )
+    (br_table $block$6$break $block$6$break $block$6$break $switch$3$default
+     (get_local $0)
     )
-    (br $block$6$break)
    )
    (call $switch
     (i32.const 2)
diff --git a/test/passes/remove-unused-brs.txt b/test/passes/remove-unused-brs.txt
index 3f4528a5c..a44a62c20 100644
--- a/test/passes/remove-unused-brs.txt
+++ b/test/passes/remove-unused-brs.txt
@@ -1675,6 +1675,7 @@
      )
     )
    )
+   (call $trim-switch)
   )
  )
  (func $same-target-br_if-and-br (; 67 ;) (type $1)
@@ -2129,4 +2130,82 @@
    )
   )
  )
+ (func $switch-to-br (; 97 ;) (type $1)
+  (block $A
+   (block $y
+    (block
+     (drop
+      (i32.const 0)
+     )
+     (br $A)
+    )
+   )
+  )
+ )
+ (func $switch-to-br-value (; 98 ;) (type $2) (result i32)
+  (block $A (result i32)
+   (block $y (result i32)
+    (block
+     (drop
+      (i32.const 1)
+     )
+     (br $A
+      (i32.const 0)
+     )
+    )
+   )
+  )
+ )
+ (func $switch-threading-multi (; 99 ;) (type $3) (param $x i32) (param $y i32) (result i32)
+  (block $block$5$break
+   (block $block$4$break
+    (loop $shape$1$continue
+     (block $block$3$break
+      (block $switch$2$case$5
+       (block $switch$2$case$4
+        (block $switch$2$default
+         (block $switch$2$case$2
+          (br_table $shape$1$continue $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$5$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$3$break $block$4$break $block$3$break
+           (get_local $x)
+          )
+         )
+         (br $shape$1$continue)
+        )
+        (br $block$3$break)
+       )
+       (br $block$4$break)
+      )
+      (br $block$5$break)
+     )
+    )
+    (unreachable)
+   )
+   (set_local $y
+    (i32.const 1)
+   )
+   (unreachable)
+  )
+  (set_local $y
+   (i32.const 2)
+  )
+  (unreachable)
+ )
+ (func $fuzz-type-changes-in-our-cycles (; 100 ;) (type $2) (result i32)
+  (loop $label$1
+   (if
+    (i32.const 0)
+    (if
+     (i32.const 0)
+     (block $label$3
+      (block $block
+      )
+     )
+     (return
+      (i32.const -8192)
+     )
+    )
+   )
+   (br $label$1)
+  )
+ )
 )
diff --git a/test/passes/remove-unused-brs.wast b/test/passes/remove-unused-brs.wast
index ea3e5f320..7a1943c14 100644
--- a/test/passes/remove-unused-brs.wast
+++ b/test/passes/remove-unused-brs.wast
@@ -1355,6 +1355,7 @@
           (i32.const 0)
         )
       )
+      (call $trim-switch)
     )
   )
   (func $same-target-br_if-and-br
@@ -1741,5 +1742,78 @@
     )
    )
   )
+  (func $switch-to-br
+    (block $A
+      (block $y
+        (br_table $y $y $A $A
+          (i32.const 0)
+        )
+      )
+    )
+  )
+  (func $switch-to-br-value (result i32)
+    (block $A (result i32)
+      (block $y (result i32)
+        (br_table $A $A $A
+          (i32.const 0)
+          (i32.const 1)
+        )
+      )
+    )
+  )
+  (func $switch-threading-multi (param $x i32) (param $y i32) (result i32)
+   (block $block$5$break
+    (block $block$4$break
+     (loop $shape$1$continue
+      (block $block$3$break
+       (block $switch$2$case$5
+        (block $switch$2$case$4
+         (block $switch$2$default
+          (block $switch$2$case$2
+           (br_table $switch$2$case$2 $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$case$5 $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$default $switch$2$case$4 $switch$2$default
+            (get_local $x)
+           )
+          )
+          (br $shape$1$continue)
+         )
+         (br $block$3$break)
+        ) ;; switch$2$case$4
+        (br $block$4$break)
+       )
+       (br $block$5$break)
+      )
+     )
+     (unreachable)
+    ) ;; block$4$break
+    (set_local $y
+     (i32.const 1)
+    )
+    (unreachable)
+   )
+   (set_local $y
+    (i32.const 2)
+   )
+   (unreachable)
+  )
+  (func $fuzz-type-changes-in-our-cycles (result i32)
+   (loop $label$1
+    (if
+     (i32.const 0)
+     (block $label$3
+      (if
+       (i32.const 0)
+       (block
+        (nop)
+        (br $label$3)
+       )
+       (return
+        (i32.const -8192)
+       )
+      )
+     )
+    )
+    (br $label$1)
+   )
+  )
 )
 
diff --git a/test/unit.fromasm b/test/unit.fromasm
index 691c65136..3eb75dc5a 100644
--- a/test/unit.fromasm
+++ b/test/unit.fromasm
@@ -182,37 +182,16 @@
     (i32.const 51)
    )
   )
-  (block $switch-case4
-   (drop
-    (i32.add
-     (get_local $0)
-     (i32.const -5)
-    )
-   )
-   (br $switch-case4)
-  )
   (loop $label$continue$L1
    (block $label$break$L1
     (loop $label$continue$L3
      (block $label$break$L3
-      (block $switch-default
-       (block $switch-case13
-        (block $switch-case12
-         (block $switch-case11
-          (br_table $switch-case11 $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-case13 $switch-default $switch-default $switch-default $switch-default $switch-default $switch-case12 $switch-default
-           (i32.sub
-            (get_local $0)
-            (i32.const -1)
-           )
-          )
-         )
-         (br $label$break$L1)
-        )
-        (br $label$continue$L3)
+      (br_table $label$break$L3 $label$break$L1 $label$break$L1 $label$break$L1 $label$break$L1 $label$break$L1 $label$continue$L3 $label$break$L1
+       (i32.add
+        (get_local $0)
+        (i32.const -110)
        )
-       (br $label$break$L3)
       )
-      (br $label$break$L1)
      )
     )
     (call $h
diff --git a/test/unit.fromasm.clamp b/test/unit.fromasm.clamp
index 44de1e100..e34bf66e4 100644
--- a/test/unit.fromasm.clamp
+++ b/test/unit.fromasm.clamp
@@ -232,37 +232,16 @@
     (i32.const 51)
    )
   )
-  (block $switch-case4
-   (drop
-    (i32.add
-     (get_local $0)
-     (i32.const -5)
-    )
-   )
-   (br $switch-case4)
-  )
   (loop $label$continue$L1
    (block $label$break$L1
     (loop $label$continue$L3
      (block $label$break$L3
-      (block $switch-default
-       (block $switch-case13
-        (block $switch-case12
-         (block $switch-case11
-          (br_table $switch-case11 $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-case13 $switch-default $switch-default $switch-default $switch-default $switch-default $switch-case12 $switch-default
-           (i32.sub
-            (get_local $0)
-            (i32.const -1)
-           )
-          )
-         )
-         (br $label$break$L1)
-        )
-        (br $label$continue$L3)
+      (br_table $label$break$L3 $label$break$L1 $label$break$L1 $label$break$L1 $label$break$L1 $label$break$L1 $label$continue$L3 $label$break$L1
+       (i32.add
+        (get_local $0)
+        (i32.const -110)
        )
-       (br $label$break$L3)
       )
-      (br $label$break$L1)
      )
     )
     (call $h
diff --git a/test/unit.fromasm.imprecise b/test/unit.fromasm.imprecise
index d9cd05f28..04794f28f 100644
--- a/test/unit.fromasm.imprecise
+++ b/test/unit.fromasm.imprecise
@@ -178,37 +178,16 @@
     (i32.const 51)
    )
   )
-  (block $switch-case4
-   (drop
-    (i32.add
-     (get_local $0)
-     (i32.const -5)
-    )
-   )
-   (br $switch-case4)
-  )
   (loop $label$continue$L1
    (block $label$break$L1
     (loop $label$continue$L3
      (block $label$break$L3
-      (block $switch-default
-       (block $switch-case13
-        (block $switch-case12
-         (block $switch-case11
-          (br_table $switch-case11 $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-default $switch-case13 $switch-default $switch-default $switch-default $switch-default $switch-default $switch-case12 $switch-default
-           (i32.sub
-            (get_local $0)
-            (i32.const -1)
-           )
-          )
-         )
-         (br $label$break$L1)
-        )
-        (br $label$continue$L3)
+      (br_table $label$break$L3 $label$break$L1 $label$break$L1 $label$break$L1 $label$break$L1 $label$break$L1 $label$continue$L3 $label$break$L1
+       (i32.add
+        (get_local $0)
+        (i32.const -110)
        )
-       (br $label$break$L3)
       )
-      (br $label$break$L1)
      )
     )
     (call $h