[llvm-commits] [llvm] r47594 - /llvm/trunk/lib/Target/X86/X86ISelLowering.cpp

[Evan Cheng]

On Feb 26, 2008, at 2:22 AM, Arnold Schwaighofer wrote:

> Author: arnolds
> Date: Tue Feb 26 04:21:54 2008
> New Revision: 47594
>
> URL: http://llvm.org/viewvc/llvm-project?rev=47594&view=rev
> Log:
> Add support for intermodule tail calls on x86/32bit with
> GOT-style position independent code. Before only tail calls to
> protected/hidden functions within the same module were optimized.
> Now all function calls are tail call optimized.
>
> Modified:
>    llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
>
> Modified: llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ISelLowering.cpp?rev=47594&r1=47593&r2=47594&view=diff
>
> =
> =
> =
> =
> =
> =
> =
> =
> ======================================================================
> --- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp (original)
> +++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp Tue Feb 26  
> 04:21:54 2008
> @@ -1547,9 +1547,13 @@
>   }
>
>   // ELF / PIC requires GOT in the EBX register before function  
> calls via PLT
> -  // GOT pointer.
> -  // Does not work with tail call since ebx is not restored  
> correctly by
> -  // tailcaller. TODO: at least for x86 - verify for x86-64
> +  // GOT pointer.
> +  // If we are tail calling and generating PIC/GOT style code load  
> the address
> +  // of the callee into ecx. The value in ecx is used as target of  
> the tail
> +  // jump. This is done to circumvent the ebx/callee-saved problem  
> for tail
> +  // calls on PIC/GOT architectures. Normally we would just put the  
> address of
> +  // GOT into ebx and then call target at PLT. But for tail callss ebx  
> would be
> +  // restored (since ebx is callee saved) before jumping to the  
> target at PLT.
>   if (!IsTailCall && !Is64Bit &&
>       getTargetMachine().getRelocationModel() == Reloc::PIC_ &&
>       Subtarget->isPICStyleGOT()) {
> @@ -1557,6 +1561,16 @@
>                              DAG.getNode(X86ISD::GlobalBaseReg,  
> getPointerTy()),
>                              InFlag);
>     InFlag = Chain.getValue(1);
> +  } else if (!Is64Bit && IsTailCall &&
> +             getTargetMachine().getRelocationModel() == Reloc::PIC_  
> &&
> +             Subtarget->isPICStyleGOT() ) {
> +    // Note: The actual moving to ecx is done further down.
> +    GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee);
> +    if (G &&  !G->getGlobal()->hasHiddenVisibility() &&
> +        !G->getGlobal()->hasProtectedVisibility())
> +      Callee =  LowerGlobalAddress(Callee, DAG);
> +    else if (isa<ExternalSymbolSDNode>(Callee))
> +      Callee = LowerExternalSymbol(Callee,DAG);
>   }

Please combine the if (...) } else if (...) { to
if (!Is64Bit && getTargetMachine().getRelocationModel() == Reloc::PIC_  
&& Subtarget->isPICStyleGot()) {
   if (!IsTailCall) {
   } else {
   }
}

Thanks,

Evan

>
>
>   if (Is64Bit && isVarArg) {
> @@ -1661,12 +1675,10 @@
>         getTargetMachine().getCodeModel() != CodeModel::Large)
>       Callee = DAG.getTargetExternalSymbol(S->getSymbol(),  
> getPointerTy());
>   } else if (IsTailCall) {
> -    assert(Callee.getOpcode() == ISD::LOAD &&
> -           "Function destination must be loaded into virtual  
> register");
>     unsigned Opc = Is64Bit ? X86::R9 : X86::ECX;
>
>     Chain = DAG.getCopyToReg(Chain,
> -                             DAG.getRegister(Opc, getPointerTy()) ,
> +                             DAG.getRegister(Opc, getPointerTy()),
>                              Callee,InFlag);
>     Callee = DAG.getRegister(Opc, getPointerTy());
>     // Add register as live out.
> @@ -1773,9 +1785,8 @@
> //  provided:
> //                * tailcallopt is enabled
> //                * caller/callee are fastcc
> -//                * elf/pic is disabled OR
> -//                * elf/pic enabled + callee is in module + callee  
> has
> -//                  visibility protected or hidden
> +//  On X86_64 architecture with GOT-style position independent code  
> only local
> +//  (within module) calls are supported at the moment.
> //  To keep the stack aligned according to platform abi the function
> //  GetAlignedArgumentStackSize ensures that argument delta is  
> always multiples
> //  of stack alignment. (Dynamic linkers need this - darwin's dyld  
> for example)
> @@ -1844,12 +1855,13 @@
>     unsigned CalleeCC = cast<ConstantSDNode>(Call.getOperand(1))- 
> >getValue();
>     if (CalleeCC == CallingConv::Fast && CallerCC == CalleeCC) {
>       SDOperand Callee = Call.getOperand(4);
> -      // On elf/pic %ebx needs to be livein.
> +      // On x86/32Bit PIC/GOT  tail calls are supported.
>       if (getTargetMachine().getRelocationModel() != Reloc::PIC_ ||
> -          !Subtarget->isPICStyleGOT())
> +          !Subtarget->isPICStyleGOT()|| !Subtarget->is64Bit())
>         return true;
>
> -      // Can only do local tail calls with PIC.
> +      // Can only do local tail calls (in same module, hidden or  
> protected) on
> +      // x86_64 PIC/GOT at the moment.
>       if (GlobalAddressSDNode *G =  
> dyn_cast<GlobalAddressSDNode>(Callee))
>         return G->getGlobal()->hasHiddenVisibility()
>             || G->getGlobal()->hasProtectedVisibility();
>
>
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