From 23f0267e2d56c0407f12e62df3561ecf75d74e6e Mon Sep 17 00:00:00 2001
From: Eli Friedman <eli.friedman@gmail.com>
Date: Thu, 1 Mar 2012 04:01:32 +0000
Subject: 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
---
 lib/CodeGen/CGBlocks.cpp | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

(limited to 'lib/CodeGen/CGBlocks.cpp')

diff --git a/lib/CodeGen/CGBlocks.cpp b/lib/CodeGen/CGBlocks.cpp
index f6aa9b4b48..1b35fa0ee4 100644
--- a/lib/CodeGen/CGBlocks.cpp
+++ b/lib/CodeGen/CGBlocks.cpp
@@ -622,10 +622,11 @@ llvm::Value *CodeGenFunction::EmitBlockLiteral(const BlockExpr *blockExpr) {
 
 llvm::Value *CodeGenFunction::EmitBlockLiteral(const CGBlockInfo &blockInfo) {
   // Using the computed layout, generate the actual block function.
+  bool isLambdaConv = blockInfo.getBlockDecl()->isConversionFromLambda();
   llvm::Constant *blockFn
     = CodeGenFunction(CGM).GenerateBlockFunction(CurGD, blockInfo,
                                                  CurFuncDecl, LocalDeclMap,
-                                                 InLambdaConversionToBlock);
+                                                 isLambdaConv);
   blockFn = llvm::ConstantExpr::getBitCast(blockFn, VoidPtrTy);
 
   // If there is nothing to capture, we can emit this as a global block.
@@ -700,11 +701,10 @@ llvm::Value *CodeGenFunction::EmitBlockLiteral(const CGBlockInfo &blockInfo) {
       src = Builder.CreateStructGEP(LoadBlockStruct(),
                                     enclosingCapture.getIndex(),
                                     "block.capture.addr");
-    } else if (InLambdaConversionToBlock) {
+    } else if (blockDecl->isConversionFromLambda()) {
       // The lambda capture in a lambda's conversion-to-block-pointer is
-      // special; we know its argument is an lvalue we can simply emit.
-      CXXConstructExpr *CE = cast<CXXConstructExpr>(ci->getCopyExpr());
-      src = EmitLValue(CE->getArg(0)).getAddress();
+      // special; we'll simply emit it directly.
+      src = 0;
     } else {
       // This is a [[type]]*.
       src = LocalDeclMap[variable];
@@ -726,7 +726,19 @@ llvm::Value *CodeGenFunction::EmitBlockLiteral(const CGBlockInfo &blockInfo) {
 
     // If we have a copy constructor, evaluate that into the block field.
     } else if (const Expr *copyExpr = ci->getCopyExpr()) {
-      EmitSynthesizedCXXCopyCtor(blockField, src, copyExpr);
+      if (blockDecl->isConversionFromLambda()) {
+        // If we have a lambda conversion, emit the expression
+        // directly into the block instead.
+        CharUnits Align = getContext().getTypeAlignInChars(type);
+        AggValueSlot Slot =
+            AggValueSlot::forAddr(blockField, Align, Qualifiers(),
+                                  AggValueSlot::IsDestructed,
+                                  AggValueSlot::DoesNotNeedGCBarriers,
+                                  AggValueSlot::IsNotAliased);
+        EmitAggExpr(copyExpr, Slot);
+      } else {
+        EmitSynthesizedCXXCopyCtor(blockField, src, copyExpr);
+      }
 
     // If it's a reference variable, copy the reference into the block field.
     } else if (type->isReferenceType()) {
-- 
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