Merge pull request #699 from WebAssembly/opts

Fuzz bug fixes

3 files changed, 14 insertions, 14 deletions

diff --git a/src/asm2wasm.h b/src/asm2wasm.h
index eb5413e20..bce67a582 100644
--- a/src/asm2wasm.h
+++ b/src/asm2wasm.h
@@ -878,7 +878,7 @@ void Asm2WasmBuilder::processAsm(Ref ast) {
     Name tempRet0;
     {
       Expression* curr = wasm.getFunction(getTempRet0)->body;
-      if (curr->is<Block>()) curr = curr->cast<Block>()->list[0];
+      if (curr->is<Block>()) curr = curr->cast<Block>()->list.back();
       if (curr->is<Return>()) curr = curr->cast<Return>()->value;
       auto* get = curr->cast<GetGlobal>();
       tempRet0 = get->name;
diff --git a/src/ast_utils.h b/src/ast_utils.h
index 4664f22ae..ff5d93e02 100644
--- a/src/ast_utils.h
+++ b/src/ast_utils.h
@@ -51,12 +51,14 @@ struct BreakSeeker : public PostWalker<BreakSeeker, Visitor<BreakSeeker>> {
   }
 
   static bool has(Expression* tree, Name target) {
+    if (!target.is()) return false;
     BreakSeeker breakSeeker(target);
     breakSeeker.walk(tree);
     return breakSeeker.found > 0;
   }
 
   static Index count(Expression* tree, Name target) {
+    if (!target.is()) return 0;
     BreakSeeker breakSeeker(target);
     breakSeeker.walk(tree);
     return breakSeeker.found;
@@ -425,18 +427,16 @@ struct ExpressionAnalyzer {
     return !curr->condition && !curr->value;
   }
 
-  // Checks if an expression ends with a simple break,
-  // and returns a pointer to it if so.
-  // (It might also have other internal branches.)
-  static Expression* getEndingSimpleBreak(Expression* curr) {
+  // Checks if an expression does not flow out in an obvious way.
+  // We return true if it cannot flow out. If it can flow out, we
+  // might still return true, as the analysis here is simple and fast.
+  static bool obviouslyDoesNotFlowOut(Expression* curr) {
     if (auto* br = curr->dynCast<Break>()) {
-      if (isSimple(br)) return br;
-      return nullptr;
+      if (!br->condition) return true;
+    } else if (auto* block = curr->dynCast<Block>()) {
+      if (block->list.size() > 0 && obviouslyDoesNotFlowOut(block->list.back()) && !BreakSeeker::has(block, block->name)) return true;
     }
-    if (auto* block = curr->dynCast<Block>()) {
-      if (block->list.size() > 0) return getEndingSimpleBreak(block->list.back());
-    }
-    return nullptr;
+    return false;
   }
 
   template<typename T>
diff --git a/src/passes/RemoveUnusedBrs.cpp b/src/passes/RemoveUnusedBrs.cpp
index 86a46374f..fa8ab2f6c 100644
--- a/src/passes/RemoveUnusedBrs.cpp
+++ b/src/passes/RemoveUnusedBrs.cpp
@@ -218,7 +218,7 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs, Visitor<R
         // let's try to move the code going to the top of the loop into the if-else
         if (!iff->ifFalse) {
           // we need the ifTrue to break, so it cannot reach the code we want to move
-          if (ExpressionAnalyzer::getEndingSimpleBreak(iff->ifTrue)) {
+          if (ExpressionAnalyzer::obviouslyDoesNotFlowOut(iff->ifTrue)) {
             iff->ifFalse = builder.stealSlice(block, i + 1, list.size());
             return true;
           }
@@ -226,10 +226,10 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs, Visitor<R
           // this is already an if-else. if one side is a dead end, we can append to the other, if
           // there is no returned value to concern us
           assert(!isConcreteWasmType(iff->type)); // can't be, since in the middle of a block
-          if (ExpressionAnalyzer::getEndingSimpleBreak(iff->ifTrue)) {
+          if (ExpressionAnalyzer::obviouslyDoesNotFlowOut(iff->ifTrue)) {
             iff->ifFalse = builder.blockifyMerge(iff->ifFalse, builder.stealSlice(block, i + 1, list.size()));
             return true;
-          } else if (ExpressionAnalyzer::getEndingSimpleBreak(iff->ifFalse)) {
+          } else if (ExpressionAnalyzer::obviouslyDoesNotFlowOut(iff->ifFalse)) {
             iff->ifTrue = builder.blockifyMerge(iff->ifTrue, builder.stealSlice(block, i + 1, list.size()));
             return true;
           }