CodeGen: Have 'this'-returning constructors and destructors to take advantage of the new backend 'returned' attribute.

The backend will now use the generic 'returned' attribute to form tail calls where possible, as well as avoid save-restores of 'this' in some cases (specifically the cases that matter for the ARM C++ ABI).

This patch also reverts a prior front-end only partial implementation of these optimizations, since it's no longer required.

llvm-svn: 184205

1 files changed, 6 insertions, 10 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index 297fc655e44..e8469e64802 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -42,8 +42,7 @@ CodeGenFunction::CodeGenFunction(CodeGenModule &cgm, bool suppressNewContext)
     AutoreleaseResult(false), BlockInfo(0), BlockPointer(0),
     LambdaThisCaptureField(0), NormalCleanupDest(0), NextCleanupDestIndex(1),
     FirstBlockInfo(0), EHResumeBlock(0), ExceptionSlot(0), EHSelectorSlot(0),
-    DebugInfo(0), DisableDebugInfo(false), CalleeWithThisReturn(0),
-    DidCallStackSave(false),
+    DebugInfo(0), DisableDebugInfo(false), DidCallStackSave(false),
     IndirectBranch(0), SwitchInsn(0), CaseRangeBlock(0), UnreachableBlock(0),
     NumReturnExprs(0), NumSimpleReturnExprs(0),
     CXXABIThisDecl(0), CXXABIThisValue(0), CXXThisValue(0),
@@ -662,8 +661,12 @@ void CodeGenFunction::GenerateCode(GlobalDecl GD, llvm::Function *Fn,
   QualType ResTy = FD->getResultType();
 
   CurGD = GD;
-  if (isa<CXXMethodDecl>(FD) && cast<CXXMethodDecl>(FD)->isInstance())
+  const CXXMethodDecl *MD;
+  if ((MD = dyn_cast<CXXMethodDecl>(FD)) && MD->isInstance()) {
+    if (CGM.getCXXABI().HasThisReturn(GD))
+      ResTy = MD->getThisType(getContext());
     CGM.getCXXABI().BuildInstanceFunctionParams(*this, ResTy, Args);
+  }
 
   for (unsigned i = 0, e = FD->getNumParams(); i != e; ++i)
     Args.push_back(FD->getParamDecl(i));
@@ -672,10 +675,6 @@ void CodeGenFunction::GenerateCode(GlobalDecl GD, llvm::Function *Fn,
   if (Stmt *Body = FD->getBody()) BodyRange = Body->getSourceRange();
   CurEHLocation = BodyRange.getEnd();
 
-  // CalleeWithThisReturn keeps track of the last callee inside this function
-  // that returns 'this'. Before starting the function, we set it to null.
-  CalleeWithThisReturn = 0;
-
   // Emit the standard function prologue.
   StartFunction(GD, ResTy, Fn, FnInfo, Args, BodyRange.getBegin());
 
@@ -727,9 +726,6 @@ void CodeGenFunction::GenerateCode(GlobalDecl GD, llvm::Function *Fn,
 
   // Emit the standard function epilogue.
   FinishFunction(BodyRange.getEnd());
-  // CalleeWithThisReturn keeps track of the last callee inside this function
-  // that returns 'this'. After finishing the function, we set it to null.
-  CalleeWithThisReturn = 0;
 
   // If we haven't marked the function nothrow through other means, do
   // a quick pass now to see if we can.