Merge pull request dotnet#45262 from benaadams/async-zero-init

Call AsyncXMethodBuilder.Create prior to storing fields to elide double zeroing

src/Compilers/CSharp/Portable/Lowering/AsyncRewriter/AsyncRewriter.AsyncIteratorRewriter.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
@@ -149,15 +150,19 @@ protected override void GenerateConstructor()
                 // Produces:
                 // .ctor(int state)
                 // {
+                //     this.builder = System.Runtime.CompilerServices.AsyncIteratorMethodBuilder.Create();
                 //     this.state = state;
                 //     this.initialThreadId = {managedThreadId};
-                //     this.builder = System.Runtime.CompilerServices.AsyncIteratorMethodBuilder.Create();
                 // }
                 Debug.Assert(stateMachineType.Constructor is IteratorConstructor);
 
                 F.CurrentFunction = stateMachineType.Constructor;
                 var bodyBuilder = ArrayBuilder<BoundStatement>.GetInstance();
                 bodyBuilder.Add(F.BaseInitialization());
+
+                // this.builder = System.Runtime.CompilerServices.AsyncIteratorMethodBuilder.Create();
+                bodyBuilder.Add(GenerateCreateAndAssignBuilder());
+
                 bodyBuilder.Add(F.Assignment(F.InstanceField(stateField), F.Parameter(F.CurrentFunction.Parameters[0]))); // this.state = state;
 
                 var managedThreadId = MakeCurrentThreadId();
@@ -167,8 +172,6 @@ protected override void GenerateConstructor()
                     bodyBuilder.Add(F.Assignment(F.InstanceField(initialThreadIdField), managedThreadId));
                 }
 
-                // this.builder = System.Runtime.CompilerServices.AsyncIteratorMethodBuilder.Create();
-                bodyBuilder.Add(GenerateCreateAndAssignBuilder());
 
                 bodyBuilder.Add(F.Return());
                 F.CloseMethod(F.Block(bodyBuilder.ToImmutableAndFree()));
@@ -248,10 +251,18 @@ protected override BoundStatement InitializeParameterField(MethodSymbol getEnume
                 return result;
             }
 
-            protected override BoundStatement GenerateStateMachineCreation(LocalSymbol stateMachineVariable, NamedTypeSymbol frameType)
+            protected override BoundStatement GenerateStateMachineCreation(LocalSymbol stateMachineVariable, NamedTypeSymbol frameType, IReadOnlyDictionary<Symbol, CapturedSymbolReplacement> proxies)
             {
+                var bodyBuilder = ArrayBuilder<BoundStatement>.GetInstance();
+
+                bodyBuilder.Add(GenerateParameterStorage(stateMachineVariable, proxies));
+
                 // return local;
-                return F.Block(F.Return(F.Local(stateMachineVariable)));
+                bodyBuilder.Add(
+                    F.Return(
+                        F.Local(stateMachineVariable)));
+
+                return F.Block(bodyBuilder.ToImmutableAndFree());
             }
 
             /// <summary>

src/Compilers/CSharp/Portable/Lowering/AsyncRewriter/AsyncRewriter.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System.Collections.Generic;
 using System.Collections.Immutable;
 using Microsoft.CodeAnalysis.CodeGen;
 using Microsoft.CodeAnalysis.CSharp.Symbols;
@@ -193,7 +194,7 @@ protected override void InitializeStateMachine(ArrayBuilder<BoundStatement> body
             }
         }
 
-        protected override BoundStatement GenerateStateMachineCreation(LocalSymbol stateMachineVariable, NamedTypeSymbol frameType)
+        protected override BoundStatement GenerateStateMachineCreation(LocalSymbol stateMachineVariable, NamedTypeSymbol frameType, IReadOnlyDictionary<Symbol, CapturedSymbolReplacement> proxies)
         {
             // If the async method's result type is a type parameter of the method, then the AsyncTaskMethodBuilder<T>
             // needs to use the method's type parameters inside the rewritten method body. All other methods generated
@@ -215,6 +216,8 @@ protected override BoundStatement GenerateStateMachineCreation(LocalSymbol state
                         null,
                         methodScopeAsyncMethodBuilderMemberCollection.CreateBuilder)));
 
+            bodyBuilder.Add(GenerateParameterStorage(stateMachineVariable, proxies));
+
             // local.$stateField = NotStartedStateMachine
             bodyBuilder.Add(
                 F.Assignment(

src/Compilers/CSharp/Portable/Lowering/IteratorRewriter/IteratorRewriter.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Diagnostics;
 using Microsoft.CodeAnalysis.CodeGen;
@@ -289,9 +290,18 @@ protected override void InitializeStateMachine(ArrayBuilder<BoundStatement> body
                     F.New(stateMachineType.Constructor.AsMember(frameType), F.Literal(initialState))));
         }
 
-        protected override BoundStatement GenerateStateMachineCreation(LocalSymbol stateMachineVariable, NamedTypeSymbol frameType)
+        protected override BoundStatement GenerateStateMachineCreation(LocalSymbol stateMachineVariable, NamedTypeSymbol frameType, IReadOnlyDictionary<Symbol, CapturedSymbolReplacement> proxies)
         {
-            return F.Return(F.Local(stateMachineVariable));
+            var bodyBuilder = ArrayBuilder<BoundStatement>.GetInstance();
+
+            bodyBuilder.Add(GenerateParameterStorage(stateMachineVariable, proxies));
+
+            // return local;
+            bodyBuilder.Add(
+                F.Return(
+                    F.Local(stateMachineVariable)));
+
+            return F.Block(bodyBuilder.ToImmutableAndFree());
         }
 
         private void GenerateMoveNextAndDispose(

src/Compilers/CSharp/Portable/Lowering/StateMachineRewriter/StateMachineRewriter.cs

@@ -75,7 +75,7 @@ protected StateMachineRewriter(
         /// <summary>
         /// Generate implementation-specific state machine initialization for the kickoff method body.
         /// </summary>
-        protected abstract BoundStatement GenerateStateMachineCreation(LocalSymbol stateMachineVariable, NamedTypeSymbol frameType);
+        protected abstract BoundStatement GenerateStateMachineCreation(LocalSymbol stateMachineVariable, NamedTypeSymbol frameType, IReadOnlyDictionary<Symbol, CapturedSymbolReplacement> proxies);
 
         /// <summary>
         /// Generate implementation-specific state machine member method implementations.
@@ -283,6 +283,17 @@ private BoundStatement GenerateKickoffMethodBody()
             // plus code to initialize all of the parameter proxies result.proxy
             var proxies = PreserveInitialParameterValuesAndThreadId ? initialParameters : nonReusableLocalProxies;
 
+            bodyBuilder.Add(GenerateStateMachineCreation(stateMachineVariable, frameType, proxies));
+
+            return F.Block(
+                ImmutableArray.Create(stateMachineVariable),
+                bodyBuilder.ToImmutableAndFree());
+        }
+
+        protected BoundStatement GenerateParameterStorage(LocalSymbol stateMachineVariable, IReadOnlyDictionary<Symbol, CapturedSymbolReplacement> proxies)
+        {
+            var bodyBuilder = ArrayBuilder<BoundStatement>.GetInstance();
+
             // starting with the "this" proxy
             if (!method.IsStatic)
             {
@@ -305,10 +316,7 @@ private BoundStatement GenerateKickoffMethodBody()
                 }
             }
 
-            bodyBuilder.Add(GenerateStateMachineCreation(stateMachineVariable, frameType));
-            return F.Block(
-                ImmutableArray.Create(stateMachineVariable),
-                bodyBuilder.ToImmutableAndFree());
+            return F.Block(bodyBuilder.ToImmutableAndFree());
         }
 
         protected SynthesizedImplementationMethod OpenMethodImplementation(

src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenAsyncIteratorTests.cs

@@ -2371,14 +2371,14 @@ .maxstack  2
   IL_0001:  call       ""object..ctor()""
   IL_0006:  nop
   IL_0007:  ldarg.0
-  IL_0008:  ldarg.1
-  IL_0009:  stfld      ""int C.<M>d__0.<>1__state""
-  IL_000e:  ldarg.0
-  IL_000f:  call       ""int System.Environment.CurrentManagedThreadId.get""
-  IL_0014:  stfld      ""int C.<M>d__0.<>l__initialThreadId""
+  IL_0008:  call       ""System.Runtime.CompilerServices.AsyncIteratorMethodBuilder System.Runtime.CompilerServices.AsyncIteratorMethodBuilder.Create()""
+  IL_000d:  stfld      ""System.Runtime.CompilerServices.AsyncIteratorMethodBuilder C.<M>d__0.<>t__builder""
+  IL_0012:  ldarg.0
+  IL_0013:  ldarg.1
+  IL_0014:  stfld      ""int C.<M>d__0.<>1__state""
   IL_0019:  ldarg.0
-  IL_001a:  call       ""System.Runtime.CompilerServices.AsyncIteratorMethodBuilder System.Runtime.CompilerServices.AsyncIteratorMethodBuilder.Create()""
-  IL_001f:  stfld      ""System.Runtime.CompilerServices.AsyncIteratorMethodBuilder C.<M>d__0.<>t__builder""
+  IL_001a:  call       ""int System.Environment.CurrentManagedThreadId.get""
+  IL_001f:  stfld      ""int C.<M>d__0.<>l__initialThreadId""
   IL_0024:  ret
 }", sequencePoints: "C+<M>d__0..ctor", source: source);
                 }
@@ -2391,14 +2391,14 @@ .maxstack  2
   IL_0000:  ldarg.0
   IL_0001:  call       ""object..ctor()""
   IL_0006:  ldarg.0
-  IL_0007:  ldarg.1
-  IL_0008:  stfld      ""int C.<M>d__0.<>1__state""
-  IL_000d:  ldarg.0
-  IL_000e:  call       ""int System.Environment.CurrentManagedThreadId.get""
-  IL_0013:  stfld      ""int C.<M>d__0.<>l__initialThreadId""
+  IL_0007:  call       ""System.Runtime.CompilerServices.AsyncIteratorMethodBuilder System.Runtime.CompilerServices.AsyncIteratorMethodBuilder.Create()""
+  IL_000c:  stfld      ""System.Runtime.CompilerServices.AsyncIteratorMethodBuilder C.<M>d__0.<>t__builder""
+  IL_0011:  ldarg.0
+  IL_0012:  ldarg.1
+  IL_0013:  stfld      ""int C.<M>d__0.<>1__state""
   IL_0018:  ldarg.0
-  IL_0019:  call       ""System.Runtime.CompilerServices.AsyncIteratorMethodBuilder System.Runtime.CompilerServices.AsyncIteratorMethodBuilder.Create()""
-  IL_001e:  stfld      ""System.Runtime.CompilerServices.AsyncIteratorMethodBuilder C.<M>d__0.<>t__builder""
+  IL_0019:  call       ""int System.Environment.CurrentManagedThreadId.get""
+  IL_001e:  stfld      ""int C.<M>d__0.<>l__initialThreadId""
   IL_0023:  ret
 }", sequencePoints: "C+<M>d__0..ctor", source: source);
                 }

src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenAsyncTests.cs

@@ -2575,11 +2575,11 @@ public static void Main()
   .maxstack  2
   .locals init (Test.<F>d__1 V_0)
   IL_0000:  ldloca.s   V_0
-  IL_0002:  ldarg.0
-  IL_0003:  stfld      ""System.Threading.AutoResetEvent Test.<F>d__1.handle""
-  IL_0008:  ldloca.s   V_0
-  IL_000a:  call       ""System.Runtime.CompilerServices.AsyncVoidMethodBuilder System.Runtime.CompilerServices.AsyncVoidMethodBuilder.Create()""
-  IL_000f:  stfld      ""System.Runtime.CompilerServices.AsyncVoidMethodBuilder Test.<F>d__1.<>t__builder""
+  IL_0002:  call       ""System.Runtime.CompilerServices.AsyncVoidMethodBuilder System.Runtime.CompilerServices.AsyncVoidMethodBuilder.Create()""
+  IL_0007:  stfld      ""System.Runtime.CompilerServices.AsyncVoidMethodBuilder Test.<F>d__1.<>t__builder""
+  IL_000c:  ldloca.s   V_0
+  IL_000e:  ldarg.0
+  IL_000f:  stfld      ""System.Threading.AutoResetEvent Test.<F>d__1.handle""
   IL_0014:  ldloca.s   V_0
   IL_0016:  ldc.i4.m1
   IL_0017:  stfld      ""int Test.<F>d__1.<>1__state""

src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenDisplayClassOptimisationTests.cs

@@ -1678,11 +1678,11 @@ .locals init (
 			[0] valuetype Program/'<M>d__0'
 		)
 		IL_0000: ldloca.s 0
-		IL_0002: ldarg.0
-		IL_0003: stfld class C Program/'<M>d__0'::enumerable
-		IL_0008: ldloca.s 0
-		IL_000a: call valuetype [mscorlib]System.Runtime.CompilerServices.AsyncVoidMethodBuilder [mscorlib]System.Runtime.CompilerServices.AsyncVoidMethodBuilder::Create()
-		IL_000f: stfld valuetype [mscorlib]System.Runtime.CompilerServices.AsyncVoidMethodBuilder Program/'<M>d__0'::'<>t__builder'
+ 		IL_0002: call valuetype [mscorlib]System.Runtime.CompilerServices.AsyncVoidMethodBuilder [mscorlib]System.Runtime.CompilerServices.AsyncVoidMethodBuilder::Create()
+ 		IL_0007: stfld valuetype [mscorlib]System.Runtime.CompilerServices.AsyncVoidMethodBuilder Program/'<M>d__0'::'<>t__builder'
+ 		IL_000c: ldloca.s 0
+ 		IL_000e: ldarg.0
+ 		IL_000f: stfld class C Program/'<M>d__0'::enumerable
 		IL_0014: ldloca.s 0
 		IL_0016: ldc.i4.m1
 		IL_0017: stfld int32 Program/'<M>d__0'::'<>1__state'

src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenScriptTests.cs

@@ -503,11 +503,11 @@ .locals init (<<Initialize>>d__0 V_0)
   IL_0000:  newobj     ""<<Initialize>>d__0..ctor()""
   IL_0005:  stloc.0
   IL_0006:  ldloc.0
-  IL_0007:  ldarg.0
-  IL_0008:  stfld      ""Script <<Initialize>>d__0.<>4__this""
-  IL_000d:  ldloc.0
-  IL_000e:  call       ""System.Runtime.CompilerServices.AsyncTaskMethodBuilder<object> System.Runtime.CompilerServices.AsyncTaskMethodBuilder<object>.Create()""
-  IL_0013:  stfld      ""System.Runtime.CompilerServices.AsyncTaskMethodBuilder<object> <<Initialize>>d__0.<>t__builder""
+  IL_0007:  call       ""System.Runtime.CompilerServices.AsyncTaskMethodBuilder<object> System.Runtime.CompilerServices.AsyncTaskMethodBuilder<object>.Create()""
+  IL_000c:  stfld      ""System.Runtime.CompilerServices.AsyncTaskMethodBuilder<object> <<Initialize>>d__0.<>t__builder""
+  IL_0011:  ldloc.0
+  IL_0012:  ldarg.0
+  IL_0013:  stfld      ""Script <<Initialize>>d__0.<>4__this""
   IL_0018:  ldloc.0
   IL_0019:  ldc.i4.m1
   IL_001a:  stfld      ""int <<Initialize>>d__0.<>1__state""
@@ -563,11 +563,11 @@ .locals init (<<Initialize>>d__0 V_0)
   IL_0000:  newobj     ""<<Initialize>>d__0..ctor()""
   IL_0005:  stloc.0
   IL_0006:  ldloc.0
-  IL_0007:  ldarg.0
-  IL_0008:  stfld      ""Script <<Initialize>>d__0.<>4__this""
-  IL_000d:  ldloc.0
-  IL_000e:  call       ""System.Runtime.CompilerServices.AsyncTaskMethodBuilder<object> System.Runtime.CompilerServices.AsyncTaskMethodBuilder<object>.Create()""
-  IL_0013:  stfld      ""System.Runtime.CompilerServices.AsyncTaskMethodBuilder<object> <<Initialize>>d__0.<>t__builder""
+  IL_0007:  call       ""System.Runtime.CompilerServices.AsyncTaskMethodBuilder<object> System.Runtime.CompilerServices.AsyncTaskMethodBuilder<object>.Create()""
+  IL_000c:  stfld      ""System.Runtime.CompilerServices.AsyncTaskMethodBuilder<object> <<Initialize>>d__0.<>t__builder""
+  IL_0011:  ldloc.0
+  IL_0012:  ldarg.0
+  IL_0013:  stfld      ""Script <<Initialize>>d__0.<>4__this""
   IL_0018:  ldloc.0
   IL_0019:  ldc.i4.m1
   IL_001a:  stfld      ""int <<Initialize>>d__0.<>1__state""

src/Compilers/CSharp/Test/Emit/Emit/EditAndContinue/LocalSlotMappingTests.cs

@@ -4232,11 +4232,11 @@ .locals init (C.<G>d__0 V_0)
      ~IL_0000:  newobj     ""C.<G>d__0..ctor()""
       IL_0005:  stloc.0
       IL_0006:  ldloc.0
-     ~IL_0007:  ldarg.0
-      IL_0008:  stfld      ""object C.<G>d__0.o""
-      IL_000d:  ldloc.0
-      IL_000e:  call       ""System.Runtime.CompilerServices.AsyncTaskMethodBuilder<object> System.Runtime.CompilerServices.AsyncTaskMethodBuilder<object>.Create()""
-      IL_0013:  stfld      ""System.Runtime.CompilerServices.AsyncTaskMethodBuilder<object> C.<G>d__0.<>t__builder""
+     ~IL_0007:  call       ""System.Runtime.CompilerServices.AsyncTaskMethodBuilder<object> System.Runtime.CompilerServices.AsyncTaskMethodBuilder<object>.Create()""
+      IL_000c:  stfld      ""System.Runtime.CompilerServices.AsyncTaskMethodBuilder<object> C.<G>d__0.<>t__builder""
+      IL_0011:  ldloc.0
+      IL_0012:  ldarg.0
+      IL_0013:  stfld      ""object C.<G>d__0.o""
       IL_0018:  ldloc.0
      -IL_0019:  ldc.i4.m1
      -IL_001a:  stfld      ""int C.<G>d__0.<>1__state""
@@ -4292,11 +4292,11 @@ .locals init (C.<G>d__0 V_0)
      ~IL_0000:  newobj     ""C.<G>d__0..ctor()""
       IL_0005:  stloc.0
       IL_0006:  ldloc.0
-     ~IL_0007:  ldarg.0
-      IL_0008:  stfld      ""System.Threading.Tasks.Task<object> C.<G>d__0.o""
-      IL_000d:  ldloc.0
-     -IL_000e:  call       ""System.Runtime.CompilerServices.AsyncTaskMethodBuilder<object> System.Runtime.CompilerServices.AsyncTaskMethodBuilder<object>.Create()""
-      IL_0013:  stfld      ""System.Runtime.CompilerServices.AsyncTaskMethodBuilder<object> C.<G>d__0.<>t__builder""
+     ~IL_0007:  call       ""System.Runtime.CompilerServices.AsyncTaskMethodBuilder<object> System.Runtime.CompilerServices.AsyncTaskMethodBuilder<object>.Create()""
+      IL_000c:  stfld      ""System.Runtime.CompilerServices.AsyncTaskMethodBuilder<object> C.<G>d__0.<>t__builder""
+      IL_0011:  ldloc.0
+      IL_0012:  ldarg.0
+      IL_0013:  stfld      ""System.Threading.Tasks.Task<object> C.<G>d__0.o""
       IL_0018:  ldloc.0
       IL_0019:  ldc.i4.m1
       IL_001a:  stfld      ""int C.<G>d__0.<>1__state""

src/Compilers/CSharp/Test/Semantic/Semantics/BindingAsyncTasklikeMoreTests.cs

@@ -141,11 +141,11 @@ .locals init (C.<G>d__1<T> V_0)
   IL_0000:  newobj     ""C.<G>d__1<T>..ctor()""
   IL_0005:  stloc.0
   IL_0006:  ldloc.0
-  IL_0007:  ldarg.0
-  IL_0008:  stfld      ""T C.<G>d__1<T>.t""
-  IL_000d:  ldloc.0
-  IL_000e:  call       ""MyTaskMethodBuilder<T> MyTaskMethodBuilder<T>.Create()""
-  IL_0013:  stfld      ""MyTaskMethodBuilder<T> C.<G>d__1<T>.<>t__builder""
+  IL_0007:  call       ""MyTaskMethodBuilder<T> MyTaskMethodBuilder<T>.Create()""
+  IL_000c:  stfld      ""MyTaskMethodBuilder<T> C.<G>d__1<T>.<>t__builder""
+  IL_0011:  ldloc.0
+  IL_0012:  ldarg.0
+  IL_0013:  stfld      ""T C.<G>d__1<T>.t""
   IL_0018:  ldloc.0
   IL_0019:  ldc.i4.m1
   IL_001a:  stfld      ""int C.<G>d__1<T>.<>1__state""