llvm dev - Oct 2011 - [LLVMdev] Problem in TwoAddressInstructionPass::runOnMachineFunction regarding subRegs

Hi,

It seems to me that the TwoAddressInstructionPass::runOnMachineFunction 
method has some problems when the tied destination register has a subReg.

The two changes below improves the situation for me but I'm all new to 
this so I'm not sure how it's supposed to work. I'm running on 2.9.

Any comments?

@@ -1172,12 +1172,20 @@ bool 
TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) {
              unsigned regASubIdx = mi->getOperand(DstIdx).getSubReg();
              TII->reMaterialize(*mbbi, mi, regA, regASubIdx, DefMI, *TRI);
              ReMatRegs.set(TargetRegisterInfo::virtReg2Index(regB));
              ++NumReMats;
            } else {
-            BuildMI(*mbbi, mi, mi->getDebugLoc(), 
TII->get(TargetOpcode::COPY),
-                    regA).addReg(regB);
+            unsigned regASubIdx = mi->getOperand(DstIdx).getSubReg();
+            if (regASubIdx) {
+              BuildMI(*mbbi, mi, mi->getDebugLoc(),
+                      TII->get(TargetOpcode::COPY)).
+                addReg(regA, RegState::Define, regASubIdx).addReg(regB);
+            }
+            else {
+              BuildMI(*mbbi, mi, mi->getDebugLoc(),
+                      TII->get(TargetOpcode::COPY), regA).addReg(regB);
+            }
            }

            MachineBasicBlock::iterator prevMI = prior(mi);
            // Update DistanceMap.
            DistanceMap.insert(std::make_pair(prevMI, Dist));
@@ -1190,11 +1198,13 @@ bool 
TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) {
                   "inconsistent operand info for 2-reg pass");
            if (MO.isKill()) {
              MO.setIsKill(false);
              RemovedKillFlag = true;
            }
+          unsigned regASubIdx = mi->getOperand(DstIdx).getSubReg();
            MO.setReg(regA);
+          MO.setSubReg(regASubIdx);
          }

/Mikael Holmén

On Oct 12, 2011, at 1:30 AM, Mikael Holmén wrote:
> Hi,
> 
> It seems to me that the TwoAddressInstructionPass::runOnMachineFunction 
> method has some problems when the tied destination register has a subReg.
> 
> The two changes below improves the situation for me but I'm all new to 
> this so I'm not sure how it's supposed to work. I'm running on
2.9.
> 
> Any comments?
Normally, sub-register defs don't exist before TwoAddressInstructionPass. 
Everything is created using INSERT_SUBREG and REG_SEQUENCE.

What does your code look like before TwoAddressInstructionPass? Is it in SSA
form, or do you have multiple defs on a virtual register?

The machine code verifier (-verify-machineinstrs) will check SSA form, but that
feature is not in 2.9.

/jakob