[llvm] 3706bda - [X86] Remove unnecessary COPY from EmitLoweredCascadedSelect.

[Craig Topper via llvm-commits]

Author: Craig Topper
Date: 2022-06-28T09:33:33-07:00
New Revision: 3706bdad4ae0fe91fbb8bb3e0acc88cf6b13ce56

URL: https://github.com/llvm/llvm-project/commit/3706bdad4ae0fe91fbb8bb3e0acc88cf6b13ce56
DIFF: https://github.com/llvm/llvm-project/commit/3706bdad4ae0fe91fbb8bb3e0acc88cf6b13ce56.diff

LOG: [X86] Remove unnecessary COPY from EmitLoweredCascadedSelect.

I believe we already checked that the destination of the first
CMOV is only used by the second CMOV so I don't think there is any
reason we need the PHI to write the register that was used by the
first CMOV. We can directly use the second CMOV destination and
avoid the copy.

This may be a left over from when the cascaded select handling
was part of the main algorithm before it was refactored in D35685.

Reviewed By: pengfei

Differential Revision: https://reviews.llvm.org/D128124

Added: 
    

Modified: 
    llvm/lib/Target/X86/X86ISelLowering.cpp

Removed: 
    


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diff  --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index a124d14f2b9de..af7af105d0863 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -34554,7 +34554,7 @@ X86TargetLowering::EmitLoweredCascadedSelect(MachineInstr &FirstCMOV,
 
   //  SinkMBB:
   //   %Result = phi [ %FalseValue, SecondInsertedMBB ], [ %TrueValue, ThisMBB ]
-  Register DestReg = FirstCMOV.getOperand(0).getReg();
+  Register DestReg = SecondCascadedCMOV.getOperand(0).getReg();
   Register Op1Reg = FirstCMOV.getOperand(1).getReg();
   Register Op2Reg = FirstCMOV.getOperand(2).getReg();
   MachineInstrBuilder MIB =
@@ -34567,11 +34567,6 @@ X86TargetLowering::EmitLoweredCascadedSelect(MachineInstr &FirstCMOV,
   // The second SecondInsertedMBB provides the same incoming value as the
   // FirstInsertedMBB (the True operand of the SELECT_CC/CMOV nodes).
   MIB.addReg(FirstCMOV.getOperand(2).getReg()).addMBB(FirstInsertedMBB);
-  // Copy the PHI result to the register defined by the second CMOV.
-  BuildMI(*SinkMBB, std::next(MachineBasicBlock::iterator(MIB.getInstr())), DL,
-          TII->get(TargetOpcode::COPY),
-          SecondCascadedCMOV.getOperand(0).getReg())
-      .addReg(FirstCMOV.getOperand(0).getReg());
 
   // Now remove the CMOVs.
   FirstCMOV.eraseFromParent();