Infer CreateThis return type in FunctionAnalysis

Summary:
If we know that `CreateThis` is being used on a JS function, then we
know it will return an object. This condition will soon be complicated
when considering classes, but that is still unlanded.

Reviewed By: avp

Differential Revision: D66544706

fbshipit-source-id: 81d7988ff08914631309728d738baa716a8f46a8

lib/Optimizer/Scalar/FunctionAnalysis.cpp

@@ -139,6 +139,11 @@ void analyzeCreateCallable(BaseCreateCallableInst *create) {
   Module *M = F->getParent();
   IRBuilder builder(M);
 
+  // The only kind of function which does not expect a made `this` parameter in
+  // a construct call is a derived class constructor.
+  bool funcExpectsThisInConstruct =
+      F->getDefinitionKind() != Function::DefinitionKind::ES6DerivedConstructor;
+
   /// Define an element in the worklist below.
   struct UserInfo {
     /// An instruction that is known to have either the value of the closure, or
@@ -170,6 +175,8 @@ void analyzeCreateCallable(BaseCreateCallableInst *create) {
   // to avoid going back and forth between the corresponding loads.
   llvh::SmallPtrSet<Instruction *, 2> visited{};
 
+  IRBuilder::InstructionDestroyer destroyer{};
+
   worklist.push_back({create, true, create->getScope()});
   while (!worklist.empty()) {
     // Instruction whose only possible closure value is the one being analyzed.
@@ -202,6 +209,17 @@ void analyzeCreateCallable(BaseCreateCallableInst *create) {
         assert(
             CTI->getClosure() == closureInst &&
             "Closure must be closure argument to CreateThisInst");
+        if (isAlwaysClosure) {
+          if (funcExpectsThisInConstruct) {
+            CTI->setType(Type::createObject());
+          } else {
+            // If a function does not expect any `this`, then we can just remove
+            // the `CreateThis` altogether since it was just going to return
+            // undefined.
+            CTI->replaceAllUsesWith(builder.getLiteralUndefined());
+            destroyer.add(CTI);
+          }
+        }
         // CreateThis leaks the closure because the created object can still
         // access the function via its parent's `.constructor` prototype.
         F->getAttributesRef(M)._allCallsitesKnownInStrictMode = false;

test/Optimizer/cache-new-object-analysis.js

@@ -36,10 +36,9 @@ return new simple(1, 2);
 // CHECK-NEXT:%BB0:
 // CHECK-NEXT:  %0 = GetParentScopeInst (:environment) %VS0: any, %parentScope: environment
 // CHECK-NEXT:  %1 = CreateFunctionInst (:object) %0: environment, %simple(): functionCode
-// CHECK-NEXT:  %2 = CreateThisInst (:undefined|object) %1: object, empty: any
-// CHECK-NEXT:  %3 = CallInst (:undefined) %1: object, %simple(): functionCode, true: boolean, empty: any, undefined: undefined, %2: undefined|object, 1: number, 2: number
-// CHECK-NEXT:  %4 = GetConstructedObjectInst (:object) %2: undefined|object, undefined: undefined
-// CHECK-NEXT:       ReturnInst %4: object
+// CHECK-NEXT:  %2 = CreateThisInst (:object) %1: object, empty: any
+// CHECK-NEXT:  %3 = CallInst (:undefined) %1: object, %simple(): functionCode, true: boolean, empty: any, undefined: undefined, %2: object, 1: number, 2: number
+// CHECK-NEXT:       ReturnInst %2: object
 // CHECK-NEXT:function_end
 
 // CHECK:function simple(x: any, y: any): undefined

test/Optimizer/callee.js

@@ -80,10 +80,9 @@ function load_store_multiple_test() {
 // CHECK-NEXT:%BB0:
 // CHECK-NEXT:  %0 = GetParentScopeInst (:environment) %VS0: any, %parentScope: environment
 // CHECK-NEXT:  %1 = CreateFunctionInst (:object) %0: environment, %"foo 1#"(): functionCode
-// CHECK-NEXT:  %2 = CreateThisInst (:undefined|object) %1: object, empty: any
-// CHECK-NEXT:  %3 = CallInst (:any) %1: object, %"foo 1#"(): functionCode, true: boolean, empty: any, undefined: undefined, %2: undefined|object, 12: number
-// CHECK-NEXT:  %4 = GetConstructedObjectInst (:object) %2: undefined|object, 12: number
-// CHECK-NEXT:       ReturnInst %4: object
+// CHECK-NEXT:  %2 = CreateThisInst (:object) %1: object, empty: any
+// CHECK-NEXT:  %3 = CallInst (:any) %1: object, %"foo 1#"(): functionCode, true: boolean, empty: any, undefined: undefined, %2: object, 12: number
+// CHECK-NEXT:       ReturnInst %2: object
 // CHECK-NEXT:function_end
 
 // CHECK:scope %VS1 [k: object]

test/Optimizer/constructor_callee.js

@@ -50,10 +50,9 @@ function ctor_load_store_test() {
 // CHECK-NEXT:%BB0:
 // CHECK-NEXT:  %0 = GetParentScopeInst (:environment) %VS0: any, %parentScope: environment
 // CHECK-NEXT:  %1 = CreateFunctionInst (:object) %0: environment, %use_this(): functionCode
-// CHECK-NEXT:  %2 = CreateThisInst (:undefined|object) %1: object, empty: any
-// CHECK-NEXT:  %3 = CallInst (:any) %1: object, %use_this(): functionCode, true: boolean, empty: any, undefined: undefined, %2: undefined|object, 12: number
-// CHECK-NEXT:  %4 = GetConstructedObjectInst (:object) %2: undefined|object, %2: undefined|object
-// CHECK-NEXT:       ReturnInst %4: object
+// CHECK-NEXT:  %2 = CreateThisInst (:object) %1: object, empty: any
+// CHECK-NEXT:  %3 = CallInst (:any) %1: object, %use_this(): functionCode, true: boolean, empty: any, undefined: undefined, %2: object, 12: number
+// CHECK-NEXT:       ReturnInst %2: object
 // CHECK-NEXT:function_end
 
 // CHECK:scope %VS1 [use_this: object]
@@ -89,8 +88,7 @@ function ctor_load_store_test() {
 // CHECK-NEXT:%BB0:
 // CHECK-NEXT:  %0 = GetParentScopeInst (:environment) %VS1: any, %parentScope: environment
 // CHECK-NEXT:  %1 = LoadFrameInst (:object) %0: environment, [%VS1.use_this]: object
-// CHECK-NEXT:  %2 = CreateThisInst (:undefined|object) %1: object, empty: any
-// CHECK-NEXT:  %3 = CallInst (:undefined) %1: object, %"use_this 1#"(): functionCode, true: boolean, empty: any, undefined: undefined, %2: undefined|object, 12: number
-// CHECK-NEXT:  %4 = GetConstructedObjectInst (:object) %2: undefined|object, undefined: undefined
-// CHECK-NEXT:       ReturnInst %4: object
+// CHECK-NEXT:  %2 = CreateThisInst (:object) %1: object, empty: any
+// CHECK-NEXT:  %3 = CallInst (:undefined) %1: object, %"use_this 1#"(): functionCode, true: boolean, empty: any, undefined: undefined, %2: object, 12: number
+// CHECK-NEXT:       ReturnInst %2: object
 // CHECK-NEXT:function_end

test/Optimizer/constructor_callee_regexp.js

@@ -35,8 +35,8 @@ function ctor_this_test() {
 // CHECK-NEXT:%BB0:
 // CHECK-NEXT:  %0 = GetParentScopeInst (:environment) %VS0: any, %parentScope: environment
 // CHECK-NEXT:  %1 = CreateFunctionInst (:object) %0: environment, %use_this(): functionCode
-// CHECK-NEXT:  %2 = CreateThisInst (:undefined|object) %1: object, empty: any
-// CHECK-NEXT:  %3 = CallInst (:object) %1: object, %use_this(): functionCode, true: boolean, empty: any, undefined: undefined, %2: undefined|object, 12: number
+// CHECK-NEXT:  %2 = CreateThisInst (:object) %1: object, empty: any
+// CHECK-NEXT:  %3 = CallInst (:object) %1: object, %use_this(): functionCode, true: boolean, empty: any, undefined: undefined, %2: object, 12: number
 // CHECK-NEXT:       ReturnInst %3: object
 // CHECK-NEXT:function_end
 

test/Optimizer/function-analysis-construction-store.js

@@ -33,10 +33,9 @@ function main() {
 // CHECK-NEXT:%BB0:
 // CHECK-NEXT:  %0 = GetParentScopeInst (:environment) %VS0: any, %parentScope: environment
 // CHECK-NEXT:  %1 = CreateFunctionInst (:object) %0: environment, %f(): functionCode
-// CHECK-NEXT:  %2 = CreateThisInst (:undefined|object) %1: object, empty: any
-// CHECK-NEXT:  %3 = CallInst (:undefined) %1: object, %f(): functionCode, true: boolean, empty: any, undefined: undefined, %2: undefined|object
-// CHECK-NEXT:  %4 = GetConstructedObjectInst (:object) %2: undefined|object, undefined: undefined
-// CHECK-NEXT:       ReturnInst %4: object
+// CHECK-NEXT:  %2 = CreateThisInst (:object) %1: object, empty: any
+// CHECK-NEXT:  %3 = CallInst (:undefined) %1: object, %f(): functionCode, true: boolean, empty: any, undefined: undefined, %2: object
+// CHECK-NEXT:       ReturnInst %2: object
 // CHECK-NEXT:function_end
 
 // CHECK:function f(): undefined

test/Optimizer/function-analysis-construction.js

@@ -32,10 +32,9 @@ function main() {
 // CHECK-NEXT:%BB0:
 // CHECK-NEXT:  %0 = GetParentScopeInst (:environment) %VS0: any, %parentScope: environment
 // CHECK-NEXT:  %1 = CreateFunctionInst (:object) %0: environment, %f(): functionCode
-// CHECK-NEXT:  %2 = CreateThisInst (:undefined|object) %1: object, empty: any
-// CHECK-NEXT:  %3 = CallInst (:undefined) %1: object, %f(): functionCode, true: boolean, empty: any, undefined: undefined, %2: undefined|object
-// CHECK-NEXT:  %4 = GetConstructedObjectInst (:object) %2: undefined|object, undefined: undefined
-// CHECK-NEXT:       ReturnInst %4: object
+// CHECK-NEXT:  %2 = CreateThisInst (:object) %1: object, empty: any
+// CHECK-NEXT:  %3 = CallInst (:undefined) %1: object, %f(): functionCode, true: boolean, empty: any, undefined: undefined, %2: object
+// CHECK-NEXT:       ReturnInst %2: object
 // CHECK-NEXT:function_end
 
 // CHECK:function f(): undefined

test/Optimizer/function-analysis-new-target.js

@@ -35,10 +35,9 @@ function main() {
 // CHECK-NEXT:%BB0:
 // CHECK-NEXT:  %0 = GetParentScopeInst (:environment) %VS0: any, %parentScope: environment
 // CHECK-NEXT:  %1 = CreateFunctionInst (:object) %0: environment, %f(): functionCode
-// CHECK-NEXT:  %2 = CreateThisInst (:undefined|object) %1: object, empty: any
-// CHECK-NEXT:  %3 = CallInst (:undefined) %1: object, %f(): functionCode, true: boolean, empty: any, %1: object, %2: undefined|object
-// CHECK-NEXT:  %4 = GetConstructedObjectInst (:object) %2: undefined|object, undefined: undefined
-// CHECK-NEXT:       ReturnInst %4: object
+// CHECK-NEXT:  %2 = CreateThisInst (:object) %1: object, empty: any
+// CHECK-NEXT:  %3 = CallInst (:undefined) %1: object, %f(): functionCode, true: boolean, empty: any, %1: object, %2: object
+// CHECK-NEXT:       ReturnInst %2: object
 // CHECK-NEXT:function_end
 
 // CHECK:function f(): undefined

test/Optimizer/inline-new-target.js

@@ -61,8 +61,8 @@ function outer2(){
 // CHECK-NEXT:  %2 = CreateFunctionInst (:object) %1: environment, %foo(): functionCode
 // CHECK-NEXT:       StoreFrameInst %1: environment, %2: object, [%VS1.foo]: object
 // CHECK-NEXT:  %4 = CreateFunctionInst (:object) %1: environment, %bar(): functionCode
-// CHECK-NEXT:  %5 = CreateThisInst (:undefined|object) %4: object, empty: any
-// CHECK-NEXT:  %6 = CallInst (:object) %4: object, %bar(): functionCode, true: boolean, %1: environment, undefined: undefined, %5: undefined|object
+// CHECK-NEXT:  %5 = CreateThisInst (:object) %4: object, empty: any
+// CHECK-NEXT:  %6 = CallInst (:object) %4: object, %bar(): functionCode, true: boolean, %1: environment, undefined: undefined, %5: object
 // CHECK-NEXT:       ReturnInst %6: object
 // CHECK-NEXT:function_end
 
@@ -76,6 +76,6 @@ function outer2(){
 // CHECK-NEXT:%BB0:
 // CHECK-NEXT:  %0 = GetParentScopeInst (:environment) %VS1: any, %parentScope: environment
 // CHECK-NEXT:  %1 = LoadFrameInst (:object) %0: environment, [%VS1.foo]: object
-// CHECK-NEXT:  %2 = CreateThisInst (:undefined|object) %1: object, empty: any
+// CHECK-NEXT:  %2 = CreateThisInst (:object) %1: object, empty: any
 // CHECK-NEXT:       ReturnInst %1: object
 // CHECK-NEXT:function_end

test/Optimizer/inline-sibling-constructors.js

@@ -66,10 +66,9 @@ function outer() {
 // CHECK-NEXT:  %2 = LoadParamInst (:any) %y: any
 // CHECK-NEXT:  %3 = LoadParamInst (:any) %z: any
 // CHECK-NEXT:  %4 = LoadFrameInst (:object) %0: environment, [%VS1.Point]: object
-// CHECK-NEXT:  %5 = CreateThisInst (:undefined|object) %4: object, empty: any
-// CHECK-NEXT:       StorePropertyStrictInst %1: any, %5: undefined|object, "x": string
-// CHECK-NEXT:       StorePropertyStrictInst %2: any, %5: undefined|object, "y": string
-// CHECK-NEXT:       StorePropertyStrictInst %3: any, %5: undefined|object, "z": string
-// CHECK-NEXT:  %9 = GetConstructedObjectInst (:object) %5: undefined|object, undefined: undefined
-// CHECK-NEXT:        ReturnInst %9: object
+// CHECK-NEXT:  %5 = CreateThisInst (:object) %4: object, empty: any
+// CHECK-NEXT:       StorePropertyStrictInst %1: any, %5: object, "x": string
+// CHECK-NEXT:       StorePropertyStrictInst %2: any, %5: object, "y": string
+// CHECK-NEXT:       StorePropertyStrictInst %3: any, %5: object, "z": string
+// CHECK-NEXT:       ReturnInst %5: object
 // CHECK-NEXT:function_end

test/Optimizer/regress-construct.js

@@ -58,11 +58,10 @@ function main() {
 // CHECK-NEXT:       CondBranchInst %1: null|object, %BB2, %BB1
 // CHECK-NEXT:%BB1:
 // CHECK-NEXT:  %3 = LoadFrameInst (:object) %0: environment, [%VS1.y]: object
-// CHECK-NEXT:  %4 = CreateThisInst (:undefined|object) %3: object, empty: any
-// CHECK-NEXT:  %5 = GetConstructedObjectInst (:object) %4: undefined|object, undefined: undefined
-// CHECK-NEXT:       StoreFrameInst %0: environment, %5: object, [%VS1.x]: null|object
+// CHECK-NEXT:  %4 = CreateThisInst (:object) %3: object, empty: any
+// CHECK-NEXT:       StoreFrameInst %0: environment, %4: object, [%VS1.x]: null|object
 // CHECK-NEXT:       BranchInst %BB2
 // CHECK-NEXT:%BB2:
-// CHECK-NEXT:  %8 = PhiInst (:null|object) %1: null|object, %BB0, %5: object, %BB1
-// CHECK-NEXT:       ReturnInst %8: null|object
+// CHECK-NEXT:  %7 = PhiInst (:null|object) %1: null|object, %BB0, %4: object, %BB1
+// CHECK-NEXT:       ReturnInst %7: null|object
 // CHECK-NEXT:function_end