[llvm] r175688 - Kill of TransferDeadFlag - Dead copies and subreg-to-reg instructions should

[Duncan Sands]

On 21/02/13 12:21, Alexey Samsonov wrote:
> Hi, Lang!
>
> I think this is causing http://llvm.org/bugs/show_bug.cgi?id=15320. Could you
> please take a look?

Vast numbers of dragonegg buildbots are showing a miscompilation, and this
commit is in the blame list...  So I also ask you to please take a look!

Ciao, Duncan.

>
>
> On Thu, Feb 21, 2013 at 3:36 AM, Lang Hames <lhames at gmail.com
> <mailto:lhames at gmail.com>> wrote:
>
>     Author: lhames
>     Date: Wed Feb 20 17:36:57 2013
>     New Revision: 175688
>
>     URL: http://llvm.org/viewvc/llvm-project?rev=175688&view=rev
>     Log:
>     Kill of TransferDeadFlag - Dead copies and subreg-to-reg instructions should
>     just be turned into kills on the spot.
>
>
>     Modified:
>          llvm/trunk/lib/CodeGen/ExpandPostRAPseudos.cpp
>
>     Modified: llvm/trunk/lib/CodeGen/ExpandPostRAPseudos.cpp
>     URL:
>     http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/ExpandPostRAPseudos.cpp?rev=175688&r1=175687&r2=175688&view=diff
>     ==============================================================================
>     --- llvm/trunk/lib/CodeGen/ExpandPostRAPseudos.cpp (original)
>     +++ llvm/trunk/lib/CodeGen/ExpandPostRAPseudos.cpp Wed Feb 20 17:36:57 2013
>     @@ -49,8 +49,6 @@ private:
>         bool LowerSubregToReg(MachineInstr *MI);
>         bool LowerCopy(MachineInstr *MI);
>
>     -  void TransferDeadFlag(MachineInstr *MI, unsigned DstReg,
>     -                        const TargetRegisterInfo *TRI);
>         void TransferImplicitDefs(MachineInstr *MI);
>       };
>       } // end anonymous namespace
>     @@ -61,21 +59,6 @@ char &llvm::ExpandPostRAPseudosID = Expa
>       INITIALIZE_PASS(ExpandPostRA, "postrapseudos",
>                       "Post-RA pseudo instruction expansion pass", false, false)
>
>     -/// TransferDeadFlag - MI is a pseudo-instruction with DstReg dead,
>     -/// and the lowered replacement instructions immediately precede it.
>     -/// Mark the replacement instructions with the dead flag.
>     -void
>     -ExpandPostRA::TransferDeadFlag(MachineInstr *MI, unsigned DstReg,
>     -                               const TargetRegisterInfo *TRI) {
>     -  for (MachineBasicBlock::iterator MII =
>     -        prior(MachineBasicBlock::iterator(MI)); ; --MII) {
>     -    if (MII->addRegisterDead(DstReg, TRI))
>     -      break;
>     -    assert(MII != MI->getParent()->begin() &&
>     -           "copyPhysReg output doesn't reference destination register!");
>     -  }
>     -}
>     -
>       /// TransferImplicitDefs - MI is a pseudo-instruction, and the lowered
>       /// replacement instructions immediately precede it.  Copy any implicit-def
>       /// operands from MI to the replacement instruction.
>     @@ -128,17 +111,17 @@ bool ExpandPostRA::LowerSubregToReg(Mach
>           }
>           DEBUG(dbgs() << "subreg: eliminated!");
>         } else {
>     +    if (MI->getOperand(0).isDead()) {
>     +      MI->setDesc(TII->get(TargetOpcode::KILL));
>     +      DEBUG(dbgs() << "subreg: replaced by: " << *MI);
>     +      return true;
>     +    }
>           TII->copyPhysReg(*MBB, MI, MI->getDebugLoc(), DstSubReg, InsReg,
>                            MI->getOperand(2).isKill());
>     -
>           // Implicitly define DstReg for subsequent uses.
>           MachineBasicBlock::iterator CopyMI = MI;
>           --CopyMI;
>           CopyMI->addRegisterDefined(DstReg);
>     -
>     -    // Transfer the kill/dead flags, if needed.
>     -    if (MI->getOperand(0).isDead())
>     -      TransferDeadFlag(MI, DstSubReg, TRI);
>           DEBUG(dbgs() << "subreg: " << *CopyMI);
>         }
>
>     @@ -151,11 +134,18 @@ bool ExpandPostRA::LowerCopy(MachineInst
>         MachineOperand &DstMO = MI->getOperand(0);
>         MachineOperand &SrcMO = MI->getOperand(1);
>
>     +  if (DstMO.isDead()) {
>     +    DEBUG(dbgs() << "dead copy: " << *MI);
>     +    MI->setDesc(TII->get(TargetOpcode::KILL));
>     +    DEBUG(dbgs() << "replaced by: " << *MI);
>     +    return true;
>     +  }
>     +
>         if (SrcMO.getReg() == DstMO.getReg()) {
>           DEBUG(dbgs() << "identity copy: " << *MI);
>           // No need to insert an identity copy instruction, but replace with a KILL
>           // if liveness is changed.
>     -    if (DstMO.isDead() || SrcMO.isUndef() || MI->getNumOperands() > 2) {
>     +    if (SrcMO.isUndef() || MI->getNumOperands() > 2) {
>             // We must make sure the super-register gets killed. Replace the
>             // instruction with KILL.
>             MI->setDesc(TII->get(TargetOpcode::KILL));
>     @@ -171,8 +161,6 @@ bool ExpandPostRA::LowerCopy(MachineInst
>         TII->copyPhysReg(*MI->getParent(), MI, MI->getDebugLoc(),
>                          DstMO.getReg(), SrcMO.getReg(), SrcMO.isKill());
>
>     -  if (DstMO.isDead())
>     -    TransferDeadFlag(MI, DstMO.getReg(), TRI);
>         if (MI->getNumOperands() > 2)
>           TransferImplicitDefs(MI);
>         DEBUG({
>
>
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>
>
> --
> Alexey Samsonov, MSK
>
>
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