r230580 - Improvement on sized deallocation from r230160:

[Reid Kleckner]

This code ultimately went away in r232731 and we took a new approach in
r232788.

On Fri, Mar 6, 2015 at 12:08 PM, John McCall <rjmccall at apple.com> wrote:

> > On Feb 26, 2015, at 12:08 PM, John McCall <rjmccall at apple.com> wrote:
> >
> >> On Feb 25, 2015, at 3:48 PM, Larisse Voufo <lvoufo at google.com> wrote:
> >> Author: lvoufo
> >> Date: Wed Feb 25 17:48:43 2015
> >> New Revision: 230580
> >>
> >> URL: http://llvm.org/viewvc/llvm-project?rev=230580&view=rev
> >> Log:
> >> Improvement on sized deallocation from r230160:
> >> Do not declare sized deallocation functions dependently on whether it
> is found in global scope. Instead, enforce the branching in emitted code by
> (1) declaring the functions extern_weak and (2) emitting sized delete
> expressions as a branching between both forms delete.
> >>
> >> Modified:
> >>   cfe/trunk/lib/CodeGen/CGExprCXX.cpp
> >>   cfe/trunk/lib/Sema/SemaExprCXX.cpp
> >>   cfe/trunk/test/CodeGenCXX/cxx1y-sized-deallocation.cpp
> >>   cfe/trunk/test/CodeGenCXX/implicit-allocation-functions.cpp
> >>   cfe/trunk/test/CodeGenCXX/pr21754.cpp
> >>
> >> Modified: cfe/trunk/lib/CodeGen/CGExprCXX.cpp
> >> URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGExprCXX.cpp?rev=230580&r1=230579&r2=230580&view=diff
> >>
> ==============================================================================
> >> --- cfe/trunk/lib/CodeGen/CGExprCXX.cpp (original)
> >> +++ cfe/trunk/lib/CodeGen/CGExprCXX.cpp Wed Feb 25 17:48:43 2015
> >> @@ -1422,6 +1422,71 @@ CodeGenFunction::pushCallObjectDeleteCle
> >>                                        OperatorDelete, ElementType);
> >> }
> >>
> >> +static void EmitDelete(CodeGenFunction &CGF,
> >> +                              const CXXDeleteExpr *DE,
> >> +                              llvm::Value *Ptr,
> >> +                              QualType ElementType);
> >> +
> >> +static void EmitSizedDelete(CodeGenFunction &CGF,
> >> +                            const CXXDeleteExpr *DE,
> >> +                            llvm::Value *Ptr,
> >> +                            QualType ElementType,
> >> +                            FunctionDecl* UnsizedDealloc) {
> >> +
> >> +  if (CGF.getLangOpts().DefineSizedDeallocation) {
> >> +    // The delete operator in use is fixed. So simply emit the delete
> expr.
> >> +    EmitDelete(CGF, DE, Ptr, ElementType);
> >> +    return;
> >> +  }
> >> +
> >> +  assert(UnsizedDealloc && "We must be emiting a 'sized' delete expr");
> >> +
> >> +  // Branch off over the value of operator delete:
> >> +  // Use the sized form if available, and default on the unsized form
> otherwise.
> >> +  llvm::BasicBlock *ThenBlock = CGF.createBasicBlock("if.then");
> >> +  llvm::BasicBlock *ContBlock = CGF.createBasicBlock("if.end");
> >> +  llvm::BasicBlock *ElseBlock = CGF.createBasicBlock("if.else");
> >> +
> >> +  // Emit the condition.
> >> +  const FunctionDecl *OpDelFD = DE->getOperatorDelete();
> >> +  llvm::Value *OpDelAddr = CGF.CGM.GetAddrOfFunction(OpDelFD);
> >> +  //llvm::Function *OpDel = dyn_cast<llvm::Function>(OpDelAddr);
> >> +  llvm::Value *SDE = CGF.Builder.CreateIsNotNull(OpDelAddr,
> "sized.del.exists");
> >> +  CGF.Builder.CreateCondBr(SDE, ThenBlock, ElseBlock);
> >> +
> >> +  // Emit the 'then' code.
> >> +  CGF.EmitBlock(ThenBlock);
> >> +  EmitDelete(CGF, DE, Ptr, ElementType);
> >> +  CGF.EmitBranch(ContBlock);
> >> +
> >> +  // Compute the 'unsized' delete expr.
> >> +  CXXDeleteExpr * E = const_cast<CXXDeleteExpr*>(DE);
> >> +  CXXDeleteExpr *UnsizedDE =
> >> +  new (CGF.getContext()) CXXDeleteExpr(CGF.getContext().VoidTy,
> >> +                                       E->isGlobalDelete(),
> >> +                                       E->isArrayForm(),
> >> +                                       E->isArrayFormAsWritten(),
> >> +
>  E->doesUsualArrayDeleteWantSize(),
> >> +                                       UnsizedDealloc,
> >> +                                       E->getArgument(),
> >> +                                       E->getLocStart());
> >
> > Instead of doing it this way, please introduce a common function to call
> > from EmitDeleteCall and the CallArrayDelete cleanup.
> >
> > Doing it this way unnecessarily clones the object / array destruction
> code,
> > causes a useless branch when making a virtual call to the deleting
> destructor,
> > and fails to branch appropriately within a deleting destructor.
> >
> > The common function will also be a natural place in the future to check
> the
> > language that elides the dynamic check and assumes that the sized
> > deallocation function exists.  (The reverse option will be implemented by
> > having Sema just specify an unsized deallocation function.)
>
> Ping.
>
> John.
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