Implement "optimization" for lambda-to-block conversion which inlines the generated block literal for lambdas which are immediately converted to block pointer type. This simplifies the AST, avoids an unnecessary copy of the lambda and makes it much easier to avoid copying the result onto the heap.

Note that this transformation has a substantial semantic effect outside of ARC: it gives the converted lambda lifetime semantics similar to a block literal.  With ARC, the effect is much less obvious because the lifetime of blocks is already managed.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@151797 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 130 insertions, 79 deletions

diff --git a/lib/Sema/SemaDeclCXX.cpp b/lib/Sema/SemaDeclCXX.cpp
index 73df1c9457..4f0e160950 100644
--- a/lib/Sema/SemaDeclCXX.cpp
+++ b/lib/Sema/SemaDeclCXX.cpp
@@ -8825,15 +8825,6 @@ void Sema::DefineImplicitLambdaToBlockPointerConversion(
        SourceLocation CurrentLocation,
        CXXConversionDecl *Conv) 
 {
-  CXXRecordDecl *Lambda = Conv->getParent();
-  
-  // Make sure that the lambda call operator is marked used.
-  CXXMethodDecl *CallOperator 
-    = cast<CXXMethodDecl>(
-        *Lambda->lookup(
-          Context.DeclarationNames.getCXXOperatorName(OO_Call)).first);
-  CallOperator->setReferenced();
-  CallOperator->setUsed();
   Conv->setUsed();
   
   ImplicitlyDefinedFunctionScope Scope(*this, Conv);
@@ -8842,79 +8833,29 @@ void Sema::DefineImplicitLambdaToBlockPointerConversion(
   // Copy-initialize the lambda object as needed to capture it.
   Expr *This = ActOnCXXThis(CurrentLocation).take();
   Expr *DerefThis =CreateBuiltinUnaryOp(CurrentLocation, UO_Deref, This).take();
-  ExprResult Init = PerformCopyInitialization(
-                      InitializedEntity::InitializeBlock(CurrentLocation, 
-                                                         DerefThis->getType(), 
-                                                         /*NRVO=*/false),
-                      CurrentLocation, DerefThis);
-  if (!Init.isInvalid())
-    Init = ActOnFinishFullExpr(Init.take());
   
-  if (Init.isInvalid()) {
+  ExprResult BuildBlock = BuildBlockForLambdaConversion(CurrentLocation,
+                                                        Conv->getLocation(),
+                                                        Conv, DerefThis);
+
+  // If we're not under ARC, make sure we still get the _Block_copy/autorelease
+  // behavior.  Note that only the general conversion function does this
+  // (since it's unusable otherwise); in the case where we inline the
+  // block literal, it has block literal lifetime semantics.
+  if (!BuildBlock.isInvalid() && !getLangOptions().ObjCAutoRefCount)
+    BuildBlock = ImplicitCastExpr::Create(Context, BuildBlock.get()->getType(),
+                                          CK_CopyAndAutoreleaseBlockObject,
+                                          BuildBlock.get(), 0, VK_RValue);
+
+  if (BuildBlock.isInvalid()) {
     Diag(CurrentLocation, diag::note_lambda_to_block_conv);
     Conv->setInvalidDecl();
     return;
   }
-  
-  // Create the new block to be returned.
-  BlockDecl *Block = BlockDecl::Create(Context, Conv, Conv->getLocation());
-  
-  // Set the type information.
-  Block->setSignatureAsWritten(CallOperator->getTypeSourceInfo());
-  Block->setIsVariadic(CallOperator->isVariadic());
-  Block->setBlockMissingReturnType(false);
-  
-  // Add parameters.
-  SmallVector<ParmVarDecl *, 4> BlockParams;
-  for (unsigned I = 0, N = CallOperator->getNumParams(); I != N; ++I) {
-    ParmVarDecl *From = CallOperator->getParamDecl(I);
-    BlockParams.push_back(ParmVarDecl::Create(Context, Block,
-                                              From->getLocStart(),
-                                              From->getLocation(),
-                                              From->getIdentifier(),
-                                              From->getType(),
-                                              From->getTypeSourceInfo(),
-                                              From->getStorageClass(),
-                                            From->getStorageClassAsWritten(),
-                                              /*DefaultArg=*/0));
-  }
-  Block->setParams(BlockParams);
-  
-  // Add capture. The capture uses a fake variable, which doesn't correspond
-  // to any actual memory location. However, the initializer copy-initializes
-  // the lambda object.
-  TypeSourceInfo *CapVarTSI =
-      Context.getTrivialTypeSourceInfo(DerefThis->getType());
-  VarDecl *CapVar = VarDecl::Create(Context, Block, Conv->getLocation(),
-                                    Conv->getLocation(), 0,
-                                    DerefThis->getType(), CapVarTSI,
-                                    SC_None, SC_None);
-  BlockDecl::Capture Capture(/*Variable=*/CapVar, /*ByRef=*/false,
-                             /*Nested=*/false, /*Copy=*/Init.take());
-  Block->setCaptures(Context, &Capture, &Capture + 1, 
-                     /*CapturesCXXThis=*/false);
-  
-  // Add a fake function body to the block. IR generation is responsible
-  // for filling in the actual body, which cannot be expressed as an AST.
-  Block->setBody(new (Context) CompoundStmt(Context, 0, 0, 
-                                            Conv->getLocation(),
-                                            Conv->getLocation()));
-
-  // Create the block literal expression.
-  Expr *BuildBlock = new (Context) BlockExpr(Block, Conv->getConversionType());
-  ExprCleanupObjects.push_back(Block);
-  ExprNeedsCleanups = true;
 
-  // If we're not under ARC, make sure we still get the _Block_copy/autorelease
-  // behavior.
-  if (!getLangOptions().ObjCAutoRefCount)
-    BuildBlock = ImplicitCastExpr::Create(Context, BuildBlock->getType(),
-                                          CK_CopyAndAutoreleaseBlockObject,
-                                          BuildBlock, 0, VK_RValue);
-  
   // Create the return statement that returns the block from the conversion
   // function.
-  StmtResult Return = ActOnReturnStmt(Conv->getLocation(), BuildBlock);
+  StmtResult Return = ActOnReturnStmt(Conv->getLocation(), BuildBlock.get());
   if (Return.isInvalid()) {
     Diag(CurrentLocation, diag::note_lambda_to_block_conv);
     Conv->setInvalidDecl();
diff --git a/lib/Sema/SemaExprCXX.cpp b/lib/Sema/SemaExprCXX.cpp
index 84afc032c0..1893d6dfa1 100644
--- a/lib/Sema/SemaExprCXX.cpp
+++ b/lib/Sema/SemaExprCXX.cpp
@@ -4460,11 +4460,8 @@ ExprResult Sema::MaybeBindToTemporary(Expr *E) {
     // For message sends and property references, we try to find an
     // actual method.  FIXME: we should infer retention by selector in
     // cases where we don't have an actual method.
-    } else {
-      ObjCMethodDecl *D = 0;
-      if (ObjCMessageExpr *Send = dyn_cast<ObjCMessageExpr>(E)) {
-        D = Send->getMethodDecl();
-      }
+    } else if (ObjCMessageExpr *Send = dyn_cast<ObjCMessageExpr>(E)) {
+      ObjCMethodDecl *D = Send->getMethodDecl();
 
       ReturnsRetained = (D && D->hasAttr<NSReturnsRetainedAttr>());
 
@@ -4474,6 +4471,13 @@ ExprResult Sema::MaybeBindToTemporary(Expr *E) {
       if (!ReturnsRetained &&
           D && D->getMethodFamily() == OMF_performSelector)
         return Owned(E);
+    } else if (isa<CastExpr>(E) &&
+               isa<BlockExpr>(cast<CastExpr>(E)->getSubExpr())) {
+      // We hit this case with the lambda conversion-to-block optimization;
+      // we don't want any extra casts here.
+      return Owned(E);
+    } else {
+      ReturnsRetained = false;
     }
 
     // Don't reclaim an object of Class type.
@@ -5089,6 +5093,34 @@ ExprResult Sema::ActOnPseudoDestructorExpr(Scope *S, Expr *Base,
 ExprResult Sema::BuildCXXMemberCallExpr(Expr *E, NamedDecl *FoundDecl,
                                         CXXConversionDecl *Method,
                                         bool HadMultipleCandidates) {
+  if (Method->getParent()->isLambda() &&
+      Method->getConversionType()->isBlockPointerType()) {
+    // This is a lambda coversion to block pointer; check if the argument
+    // is a LambdaExpr.
+    Expr *SubE = E;
+    CastExpr *CE = dyn_cast<CastExpr>(SubE);
+    if (CE && CE->getCastKind() == CK_NoOp)
+      SubE = CE->getSubExpr();
+    SubE = SubE->IgnoreParens();
+    if (CXXBindTemporaryExpr *BE = dyn_cast<CXXBindTemporaryExpr>(SubE))
+      SubE = BE->getSubExpr();
+    if (isa<LambdaExpr>(SubE)) {
+      // For the conversion to block pointer on a lambda expression, we
+      // construct a special BlockLiteral instead; this doesn't really make
+      // a difference in ARC, but outside of ARC the resulting block literal
+      // follows the normal lifetime rules for block literals instead of being
+      // autoreleased.
+      DiagnosticErrorTrap Trap(Diags);
+      ExprResult Exp = BuildBlockForLambdaConversion(E->getExprLoc(),
+                                                     E->getExprLoc(),
+                                                     Method, E);
+      if (Exp.isInvalid())
+        Diag(E->getExprLoc(), diag::note_lambda_to_block_conv);
+      return Exp;
+    }
+  }
+      
+
   ExprResult Exp = PerformObjectArgumentInitialization(E, /*Qualifier=*/0,
                                           FoundDecl, Method);
   if (Exp.isInvalid())
diff --git a/lib/Sema/SemaLambda.cpp b/lib/Sema/SemaLambda.cpp
index b0c6a61bce..3611350de0 100644
--- a/lib/Sema/SemaLambda.cpp
+++ b/lib/Sema/SemaLambda.cpp
@@ -740,3 +740,81 @@ ExprResult Sema::ActOnLambdaExpr(SourceLocation StartLoc, Stmt *Body,
   
   return MaybeBindToTemporary(Lambda);
 }
+
+ExprResult Sema::BuildBlockForLambdaConversion(SourceLocation CurrentLocation,
+                                               SourceLocation ConvLocation,
+                                               CXXConversionDecl *Conv,
+                                               Expr *Src) {
+  // Make sure that the lambda call operator is marked used.
+  CXXRecordDecl *Lambda = Conv->getParent();
+  CXXMethodDecl *CallOperator 
+    = cast<CXXMethodDecl>(
+        *Lambda->lookup(
+          Context.DeclarationNames.getCXXOperatorName(OO_Call)).first);
+  CallOperator->setReferenced();
+  CallOperator->setUsed();
+
+  ExprResult Init = PerformCopyInitialization(
+                      InitializedEntity::InitializeBlock(ConvLocation, 
+                                                         Src->getType(), 
+                                                         /*NRVO=*/false),
+                      CurrentLocation, Src);
+  if (!Init.isInvalid())
+    Init = ActOnFinishFullExpr(Init.take());
+  
+  if (Init.isInvalid())
+    return ExprError();
+  
+  // Create the new block to be returned.
+  BlockDecl *Block = BlockDecl::Create(Context, CurContext, ConvLocation);
+
+  // Set the type information.
+  Block->setSignatureAsWritten(CallOperator->getTypeSourceInfo());
+  Block->setIsVariadic(CallOperator->isVariadic());
+  Block->setBlockMissingReturnType(false);
+
+  // Add parameters.
+  SmallVector<ParmVarDecl *, 4> BlockParams;
+  for (unsigned I = 0, N = CallOperator->getNumParams(); I != N; ++I) {
+    ParmVarDecl *From = CallOperator->getParamDecl(I);
+    BlockParams.push_back(ParmVarDecl::Create(Context, Block,
+                                              From->getLocStart(),
+                                              From->getLocation(),
+                                              From->getIdentifier(),
+                                              From->getType(),
+                                              From->getTypeSourceInfo(),
+                                              From->getStorageClass(),
+                                            From->getStorageClassAsWritten(),
+                                              /*DefaultArg=*/0));
+  }
+  Block->setParams(BlockParams);
+
+  Block->setIsConversionFromLambda(true);
+
+  // Add capture. The capture uses a fake variable, which doesn't correspond
+  // to any actual memory location. However, the initializer copy-initializes
+  // the lambda object.
+  TypeSourceInfo *CapVarTSI =
+      Context.getTrivialTypeSourceInfo(Src->getType());
+  VarDecl *CapVar = VarDecl::Create(Context, Block, ConvLocation,
+                                    ConvLocation, 0,
+                                    Src->getType(), CapVarTSI,
+                                    SC_None, SC_None);
+  BlockDecl::Capture Capture(/*Variable=*/CapVar, /*ByRef=*/false,
+                             /*Nested=*/false, /*Copy=*/Init.take());
+  Block->setCaptures(Context, &Capture, &Capture + 1, 
+                     /*CapturesCXXThis=*/false);
+
+  // Add a fake function body to the block. IR generation is responsible
+  // for filling in the actual body, which cannot be expressed as an AST.
+  Block->setBody(new (Context) CompoundStmt(Context, 0, 0, 
+                                            ConvLocation,
+                                            ConvLocation));
+
+  // Create the block literal expression.
+  Expr *BuildBlock = new (Context) BlockExpr(Block, Conv->getConversionType());
+  ExprCleanupObjects.push_back(Block);
+  ExprNeedsCleanups = true;
+
+  return BuildBlock;
+}