Remove RegisterScavenger::isSuperRegUsed(). This completely reverses the mistaken commit r77904.

Now there is no special treatment of instructions that redefine part of a
super-register. Instead, the super-register is marked with <imp-use,kill> and
<imp-def>. For instance, from LowerSubregs on ARM:

subreg: CONVERTING: %Q1<def> = INSERT_SUBREG %Q1<undef>, %D1<kill>, 5
subreg: %D2<def> = FCPYD %D1<kill>, 14, %reg0, %Q1<imp-def>

subreg: CONVERTING: %Q1<def> = INSERT_SUBREG %Q1, %D0<kill>, 6
subreg: %D3<def> = FCPYD %D0<kill>, 14, %reg0, %Q1<imp-use,kill>, %Q1<imp-def>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@78466 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 7 insertions, 6 deletions

diff --git a/lib/CodeGen/LowerSubregs.cpp b/lib/CodeGen/LowerSubregs.cpp
index 6c5052a..f34b290 100644
--- a/lib/CodeGen/LowerSubregs.cpp
+++ b/lib/CodeGen/LowerSubregs.cpp
@@ -270,14 +270,15 @@ bool LowerSubregsInstructionPass::LowerInsert(MachineInstr *MI) {
     MachineBasicBlock::iterator CopyMI = MI;
     --CopyMI;
 
+    // INSERT_SUBREG is a two-address instruction so it implicitly kills SrcReg.
+    if (!MI->getOperand(1).isUndef())
+      CopyMI->addOperand(MachineOperand::CreateReg(DstReg, false, true, true));
+
     // Transfer the kill/dead flags, if needed.
     if (MI->getOperand(0).isDead()) {
       TransferDeadFlag(MI, DstSubReg, TRI);
-      // Also add a SrcReg<imp-kill> of the super register.
-      CopyMI->addOperand(MachineOperand::CreateReg(DstReg, false, true, true));
-    } else if (MI->getOperand(1).isUndef()) {
-      // If SrcReg was marked <undef> we must make sure it is alive after this
-      // replacement.  Add a SrcReg<imp-def> operand.
+    } else {
+      // Make sure the full DstReg is live after this replacement.
       CopyMI->addOperand(MachineOperand::CreateReg(DstReg, true, true));
     }
 
@@ -293,7 +294,7 @@ bool LowerSubregsInstructionPass::LowerInsert(MachineInstr *MI) {
 
   DOUT << "\n";
   MBB->erase(MI);
-  return true;                    
+  return true;
 }
 
 /// runOnMachineFunction - Reduce subregister inserts and extracts to register