ARM: Fix CMP_SWAP expansion

Clean up after my misguided attempt in r304267 to "fix" CMP_SWAP
returning an uninitialized status value.

- I was always using tMOVi8 to zero the status register which cannot
  encode higher register numbers and llvm would silently miscompile)

- Nobody was ever looking at that status value outside the expansion.
  ARMDAGToDAGISel::SelectCMP_SWAP() the only place creating CMP_SWAP
  instructions was not mapping anything to it. (The cmpxchg status value
  from llvm IR is lowered to a manual comparison after the CMP_SWAP)

So this:
- Renames the register from "status" to "temp" it make it obvious that
  it isn't used outside the expansion.
- Remove the zeroing status/temp register.
- Keep the live-in list improvements from r304267

Fixes http://llvm.org/PR34056

llvm-svn: 310534

2 files changed, 16 insertions, 32 deletions

diff --git a/llvm/lib/Target/ARM/ARMExpandPseudoInsts.cpp b/llvm/lib/Target/ARM/ARMExpandPseudoInsts.cpp
index b17bc3f6e28..907ca496244 100644
--- a/llvm/lib/Target/ARM/ARMExpandPseudoInsts.cpp
+++ b/llvm/lib/Target/ARM/ARMExpandPseudoInsts.cpp
@@ -762,8 +762,7 @@ bool ARMExpandPseudo::ExpandCMP_SWAP(MachineBasicBlock &MBB,
   MachineInstr &MI = *MBBI;
   DebugLoc DL = MI.getDebugLoc();
   const MachineOperand &Dest = MI.getOperand(0);
-  unsigned StatusReg = MI.getOperand(1).getReg();
-  bool StatusDead = MI.getOperand(1).isDead();
+  unsigned TempReg = MI.getOperand(1).getReg();
   // Duplicating undef operands into 2 instructions does not guarantee the same
   // value on both; However undef should be replaced by xzr anyway.
   assert(!MI.getOperand(2).isUndef() && "cannot handle undef");
@@ -790,23 +789,9 @@ bool ARMExpandPseudo::ExpandCMP_SWAP(MachineBasicBlock &MBB,
   }
 
   // .Lloadcmp:
-  //     mov wStatus, #0
   //     ldrex rDest, [rAddr]
   //     cmp rDest, rDesired
   //     bne .Ldone
-  if (!StatusDead) {
-    if (IsThumb) {
-      BuildMI(LoadCmpBB, DL, TII->get(ARM::tMOVi8), StatusReg)
-        .addDef(ARM::CPSR, RegState::Dead)
-        .addImm(0)
-        .add(predOps(ARMCC::AL));
-    } else {
-      BuildMI(LoadCmpBB, DL, TII->get(ARM::MOVi), StatusReg)
-        .addImm(0)
-        .add(predOps(ARMCC::AL))
-        .add(condCodeOp());
-    }
-  }
 
   MachineInstrBuilder MIB;
   MIB = BuildMI(LoadCmpBB, DL, TII->get(LdrexOp), Dest.getReg());
@@ -829,10 +814,10 @@ bool ARMExpandPseudo::ExpandCMP_SWAP(MachineBasicBlock &MBB,
   LoadCmpBB->addSuccessor(StoreBB);
 
   // .Lstore:
-  //     strex rStatus, rNew, [rAddr]
-  //     cmp rStatus, #0
+  //     strex rTempReg, rNew, [rAddr]
+  //     cmp rTempReg, #0
   //     bne .Lloadcmp
-  MIB = BuildMI(StoreBB, DL, TII->get(StrexOp), StatusReg)
+  MIB = BuildMI(StoreBB, DL, TII->get(StrexOp), TempReg)
     .addReg(NewReg)
     .addReg(AddrReg);
   if (StrexOp == ARM::t2STREX)
@@ -841,7 +826,7 @@ bool ARMExpandPseudo::ExpandCMP_SWAP(MachineBasicBlock &MBB,
 
   unsigned CMPri = IsThumb ? ARM::t2CMPri : ARM::CMPri;
   BuildMI(StoreBB, DL, TII->get(CMPri))
-      .addReg(StatusReg, getKillRegState(StatusDead))
+      .addReg(TempReg, RegState::Kill)
       .addImm(0)
       .add(predOps(ARMCC::AL));
   BuildMI(StoreBB, DL, TII->get(Bcc))
@@ -897,8 +882,7 @@ bool ARMExpandPseudo::ExpandCMP_SWAP_64(MachineBasicBlock &MBB,
   MachineInstr &MI = *MBBI;
   DebugLoc DL = MI.getDebugLoc();
   MachineOperand &Dest = MI.getOperand(0);
-  unsigned StatusReg = MI.getOperand(1).getReg();
-  bool StatusDead = MI.getOperand(1).isDead();
+  unsigned TempReg = MI.getOperand(1).getReg();
   // Duplicating undef operands into 2 instructions does not guarantee the same
   // value on both; However undef should be replaced by xzr anyway.
   assert(!MI.getOperand(2).isUndef() && "cannot handle undef");
@@ -924,7 +908,7 @@ bool ARMExpandPseudo::ExpandCMP_SWAP_64(MachineBasicBlock &MBB,
   // .Lloadcmp:
   //     ldrexd rDestLo, rDestHi, [rAddr]
   //     cmp rDestLo, rDesiredLo
-  //     sbcs rStatus<dead>, rDestHi, rDesiredHi
+  //     sbcs rTempReg<dead>, rDestHi, rDesiredHi
   //     bne .Ldone
   unsigned LDREXD = IsThumb ? ARM::t2LDREXD : ARM::LDREXD;
   MachineInstrBuilder MIB;
@@ -952,17 +936,17 @@ bool ARMExpandPseudo::ExpandCMP_SWAP_64(MachineBasicBlock &MBB,
   LoadCmpBB->addSuccessor(StoreBB);
 
   // .Lstore:
-  //     strexd rStatus, rNewLo, rNewHi, [rAddr]
-  //     cmp rStatus, #0
+  //     strexd rTempReg, rNewLo, rNewHi, [rAddr]
+  //     cmp rTempReg, #0
   //     bne .Lloadcmp
   unsigned STREXD = IsThumb ? ARM::t2STREXD : ARM::STREXD;
-  MIB = BuildMI(StoreBB, DL, TII->get(STREXD), StatusReg);
+  MIB = BuildMI(StoreBB, DL, TII->get(STREXD), TempReg);
   addExclusiveRegPair(MIB, New, 0, IsThumb, TRI);
   MIB.addReg(AddrReg).add(predOps(ARMCC::AL));
 
   unsigned CMPri = IsThumb ? ARM::t2CMPri : ARM::CMPri;
   BuildMI(StoreBB, DL, TII->get(CMPri))
-      .addReg(StatusReg, getKillRegState(StatusDead))
+      .addReg(TempReg, RegState::Kill)
       .addImm(0)
       .add(predOps(ARMCC::AL));
   BuildMI(StoreBB, DL, TII->get(Bcc))
diff --git a/llvm/lib/Target/ARM/ARMInstrInfo.td b/llvm/lib/Target/ARM/ARMInstrInfo.td
index 25efe0ff18e..a526f043ae0 100644
--- a/llvm/lib/Target/ARM/ARMInstrInfo.td
+++ b/llvm/lib/Target/ARM/ARMInstrInfo.td
@@ -6060,21 +6060,21 @@ def SPACE : PseudoInst<(outs GPR:$Rd), (ins i32imm:$size, GPR:$Rn),
 // significantly more naive than the standard expansion: we conservatively
 // assume seq_cst, strong cmpxchg and omit clrex on failure.
 
-let Constraints = "@earlyclobber $Rd,@earlyclobber $status",
+let Constraints = "@earlyclobber $Rd,@earlyclobber $temp",
     mayLoad = 1, mayStore = 1 in {
-def CMP_SWAP_8 : PseudoInst<(outs GPR:$Rd, GPR:$status),
+def CMP_SWAP_8 : PseudoInst<(outs GPR:$Rd, GPR:$temp),
                             (ins GPR:$addr, GPR:$desired, GPR:$new),
                             NoItinerary, []>, Sched<[]>;
 
-def CMP_SWAP_16 : PseudoInst<(outs GPR:$Rd, GPR:$status),
+def CMP_SWAP_16 : PseudoInst<(outs GPR:$Rd, GPR:$temp),
                              (ins GPR:$addr, GPR:$desired, GPR:$new),
                              NoItinerary, []>, Sched<[]>;
 
-def CMP_SWAP_32 : PseudoInst<(outs GPR:$Rd, GPR:$status),
+def CMP_SWAP_32 : PseudoInst<(outs GPR:$Rd, GPR:$temp),
                              (ins GPR:$addr, GPR:$desired, GPR:$new),
                              NoItinerary, []>, Sched<[]>;
 
-def CMP_SWAP_64 : PseudoInst<(outs GPRPair:$Rd, GPR:$status),
+def CMP_SWAP_64 : PseudoInst<(outs GPRPair:$Rd, GPR:$temp),
                              (ins GPR:$addr, GPRPair:$desired, GPRPair:$new),
                              NoItinerary, []>, Sched<[]>;
 }