From d0d9a4f43dbd58c694c706b17996157fede20bdf Mon Sep 17 00:00:00 2001
From: Gaming4JC <g4jc@hyperbola.info>
Date: Fri, 13 Dec 2019 20:59:32 -0500
Subject: Bug 1316098 - Optimize out result object allocation for await/return
 in async function.

Tag #1287
---
 js/src/frontend/BytecodeEmitter.cpp | 25 ++++++++++++++++++++++---
 js/src/frontend/BytecodeEmitter.h   |  1 +
 js/src/frontend/SharedContext.h     |  2 +-
 3 files changed, 24 insertions(+), 4 deletions(-)

(limited to 'js/src/frontend')

diff --git a/js/src/frontend/BytecodeEmitter.cpp b/js/src/frontend/BytecodeEmitter.cpp
index 77a480bff..a98016d63 100644
--- a/js/src/frontend/BytecodeEmitter.cpp
+++ b/js/src/frontend/BytecodeEmitter.cpp
@@ -8552,7 +8552,7 @@ bool
 BytecodeEmitter::emitYield(ParseNode* pn)
 {
     MOZ_ASSERT(sc->isFunctionBox());
-    MOZ_ASSERT(pn->getOp() == JSOP_YIELD || pn->getOp() == JSOP_AWAIT);
+    MOZ_ASSERT(pn->getOp() == JSOP_YIELD);
 
     bool needsIteratorResult = sc->asFunctionBox()->needsIteratorResult();
     if (needsIteratorResult) {
@@ -8574,12 +8574,27 @@ BytecodeEmitter::emitYield(ParseNode* pn)
     if (!emitGetDotGenerator())
         return false;
 
-    if (!emitYieldOp(pn->getOp()))
+    if (!emitYieldOp(JSOP_YIELD))
         return false;
 
     return true;
 }
 
+bool
+BytecodeEmitter::emitAwait(ParseNode* pn)
+{
+    MOZ_ASSERT(sc->isFunctionBox());
+    MOZ_ASSERT(pn->getOp() == JSOP_AWAIT);
+
+    if (!emitTree(pn->pn_kid))
+        return false;
+    if (!emitGetDotGenerator())
+        return false;
+    if (!emitYieldOp(JSOP_AWAIT))
+        return false;
+    return true;
+}
+
 bool
 BytecodeEmitter::emitYieldStar(ParseNode* iter)
 {
@@ -10630,11 +10645,15 @@ BytecodeEmitter::emitTree(ParseNode* pn, ValueUsage valueUsage /* = ValueUsage::
         break;
 
       case PNK_YIELD:
-      case PNK_AWAIT:
         if (!emitYield(pn))
             return false;
         break;
 
+      case PNK_AWAIT:
+        if (!emitAwait(pn))
+            return false;
+        break;
+
       case PNK_STATEMENTLIST:
         if (!emitStatementList(pn))
             return false;
diff --git a/js/src/frontend/BytecodeEmitter.h b/js/src/frontend/BytecodeEmitter.h
index 08638f48a..f3f78df16 100644
--- a/js/src/frontend/BytecodeEmitter.h
+++ b/js/src/frontend/BytecodeEmitter.h
@@ -613,6 +613,7 @@ struct MOZ_STACK_CLASS BytecodeEmitter
     MOZ_MUST_USE bool emitYield(ParseNode* pn);
     MOZ_MUST_USE bool emitYieldOp(JSOp op);
     MOZ_MUST_USE bool emitYieldStar(ParseNode* iter);
+    MOZ_MUST_USE bool emitAwait(ParseNode* pn);
 
     MOZ_MUST_USE bool emitPropLHS(ParseNode* pn);
     MOZ_MUST_USE bool emitPropOp(ParseNode* pn, JSOp op);
diff --git a/js/src/frontend/SharedContext.h b/js/src/frontend/SharedContext.h
index 2d478308e..8a5f6c0bd 100644
--- a/js/src/frontend/SharedContext.h
+++ b/js/src/frontend/SharedContext.h
@@ -553,7 +553,7 @@ class FunctionBox : public ObjectBox, public SharedContext
     }
 
     bool needsIteratorResult() const {
-        return isStarGenerator() || isAsync();
+        return isStarGenerator();
     }
 
     bool isAsync() const { return asyncKind() == AsyncFunction; }
-- 
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