Merge pull request #386 from WebAssembly/improve-remove-brs

Improve RemoveBrs

1 files changed, 35 insertions, 3 deletions

diff --git a/src/passes/Vacuum.cpp b/src/passes/Vacuum.cpp
index 863d78f14..dd88fa0eb 100644
--- a/src/passes/Vacuum.cpp
+++ b/src/passes/Vacuum.cpp
@@ -21,6 +21,7 @@
 #include <wasm.h>
 #include <pass.h>
 #include <ast_utils.h>
+#include <wasm-builder.h>
 
 namespace wasm {
 
@@ -32,14 +33,26 @@ struct Vacuum : public WalkerPass<PostWalker<Vacuum, Visitor<Vacuum>>> {
     int skip = 0;
     auto& list = curr->list;
     size_t size = list.size();
+    bool needResize = false;
     for (size_t z = 0; z < size; z++) {
       if (list[z]->is<Nop>()) {
         skip++;
-      } else if (skip > 0) {
-        list[z - skip] = list[z];
+        needResize = true;
+      } else {
+        if (skip > 0) {
+          list[z - skip] = list[z];
+        }
+        // if this is an unconditional br, the rest is dead code
+        Break* br = list[z - skip]->dynCast<Break>();
+        Switch* sw = list[z - skip]->dynCast<Switch>();
+        if ((br && !br->condition) || sw) {
+          list.resize(z - skip + 1);
+          needResize = false;
+          break;
+        }
       }
     }
-    if (skip > 0) {
+    if (needResize) {
       list.resize(size - skip);
     }
     if (!curr->name.is()) {
@@ -50,6 +63,25 @@ struct Vacuum : public WalkerPass<PostWalker<Vacuum, Visitor<Vacuum>>> {
       }
     }
   }
+
+  void visitIf(If* curr) {
+    if (curr->ifFalse) {
+      if (curr->ifFalse->is<Nop>()) {
+        curr->ifFalse = nullptr;
+      } else if (curr->ifTrue->is<Nop>()) {
+        curr->ifTrue = curr->ifFalse;
+        curr->ifFalse = nullptr;
+        curr->condition = Builder(*getModule()).makeUnary(EqZ, curr->condition, curr->condition->type);
+      }
+    }
+    if (!curr->ifFalse) {
+      // no else
+      if (curr->ifTrue->is<Nop>()) {
+        // no nothing
+        replaceCurrent(curr->condition);
+      }
+    }
+  }
 };
 
 static RegisterPass<Vacuum> registerPass("vacuum", "removes obviously unneeded code");