more RemoveUnusedName opts: merge names when possible, and do block/loop merging based on their names

1 files changed, 42 insertions, 5 deletions

diff --git a/src/passes/RemoveUnusedNames.cpp b/src/passes/RemoveUnusedNames.cpp
index 5145cc744..9c6743479 100644
--- a/src/passes/RemoveUnusedNames.cpp
+++ b/src/passes/RemoveUnusedNames.cpp
@@ -15,7 +15,8 @@
  */
 
 //
-// Removes names from locations that are never branched to.
+// Removes names from locations that are never branched to, and
+// merge names when possible (by merging their blocks)
 //
 
 #include <wasm.h>
@@ -30,17 +31,17 @@ struct RemoveUnusedNames : public WalkerPass<PostWalker<RemoveUnusedNames, Visit
 
   // We maintain a list of branches that we saw in children, then when we reach
   // a parent block, we know if it was branched to
-  std::set<Name> branchesSeen;
+  std::map<Name, std::set<Expression*>> branchesSeen;
 
   void visitBreak(Break *curr) {
-    branchesSeen.insert(curr->name);
+    branchesSeen[curr->name].insert(curr);
   }
 
   void visitSwitch(Switch *curr) {
     for (auto name : curr->targets) {
-      branchesSeen.insert(name);
+      branchesSeen[name].insert(curr);
     }
-    branchesSeen.insert(curr->default_);
+    branchesSeen[curr->default_].insert(curr);
   }
 
   void handleBreakTarget(Name& name) {
@@ -54,7 +55,35 @@ struct RemoveUnusedNames : public WalkerPass<PostWalker<RemoveUnusedNames, Visit
   }
 
   void visitBlock(Block *curr) {
+    if (curr->name.is() && curr->list.size() == 1) {
+      auto* child = curr->list[0]->dynCast<Block>();
+      if (child && child->name.is()) {
+        // we have just one child, this block, so breaking out of it goes to the same place as breaking out of us, we just need one name (and block)
+        auto& branches = branchesSeen[curr->name];
+        for (auto* branch : branches) {
+          if (Break* br = branch->dynCast<Break>()) {
+            if (br->name == curr->name) br->name = child->name;
+          } else if (Switch* sw = branch->dynCast<Switch>()) {
+            for (auto& target : sw->targets) {
+              if (target == curr->name) target = child->name;
+            }
+            if (sw->default_ == curr->name) sw->default_ = child->name;
+          } else {
+            WASM_UNREACHABLE();
+          }
+        }
+        replaceCurrent(child);
+      }
+    }
     handleBreakTarget(curr->name);
+    if (curr->name.is() && curr->list.size() == 1) {
+      auto* child = curr->list[0]->dynCast<Loop>();
+      if (child && !child->out.is()) {
+        // we have just one child, this loop, and it lacks an out label. So this block's name is doing just that!
+        child->out = curr->name;
+        replaceCurrent(child);
+      }
+    }
   }
 
   void visitLoop(Loop *curr) {
@@ -68,6 +97,14 @@ struct RemoveUnusedNames : public WalkerPass<PostWalker<RemoveUnusedNames, Visit
       block->list.push_back(curr->body);
       replaceCurrent(block);
     }
+    if (curr->in.is() && !curr->out.is()) {
+      auto* child = curr->body->dynCast<Block>();
+      if (child && child->name.is()) {
+        // we have just one child, this block, and we lack an out label. So we can take the block's!
+        curr->out = child->name;
+        child->name = Name();
+      }
+    }
   }
 
   void visitFunction(Function *curr) {