RegisterCoalescer: Cleanup joinReservedPhysReg(); NFC

- Factor out a common subexpression
- Add some helpful comments
- Fix printing of a register in a debug message

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@293856 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/RegisterCoalescer.cpp b/lib/CodeGen/RegisterCoalescer.cpp
index 778ea8eaca1bdf0aaa5f5252d8f393787260ab80..f4cc37d9ca0009889bbc3c8873352230ee5fc499 100644 (file)
--- a/lib/CodeGen/RegisterCoalescer.cpp
+++ b/lib/CodeGen/RegisterCoalescer.cpp
@@ -1744,9 +1744,10 @@ bool RegisterCoalescer::joinCopy(MachineInstr *CopyMI, bool &Again) {
 
 bool RegisterCoalescer::joinReservedPhysReg(CoalescerPair &CP) {
   unsigned DstReg = CP.getDstReg();
+  unsigned SrcReg = CP.getSrcReg();
   assert(CP.isPhys() && "Must be a physreg copy");
   assert(MRI->isReserved(DstReg) && "Not a reserved register");
-  LiveInterval &RHS = LIS->getInterval(CP.getSrcReg());
+  LiveInterval &RHS = LIS->getInterval(SrcReg);
   DEBUG(dbgs() << "\t\tRHS = " << RHS << '\n');
 
   assert(RHS.containsOneValue() && "Invalid join with reserved register");
@@ -1788,17 +1789,31 @@ bool RegisterCoalescer::joinReservedPhysReg(CoalescerPair &CP) {
   // Delete the identity copy.
   MachineInstr *CopyMI;
   if (CP.isFlipped()) {
-    CopyMI = MRI->getVRegDef(RHS.reg);
+    // Physreg is copied into vreg
+    //   %vregY = COPY %X
+    //   ...  //< no other def of %X here
+    //   use %vregY
+    // =>
+    //   ...
+    //   use %X
+    CopyMI = MRI->getVRegDef(SrcReg);
   } else {
-    if (!MRI->hasOneNonDBGUse(RHS.reg)) {
+    // VReg is copied into physreg:
+    //   %vregX = def
+    //   ... //< no other def or use of %Y here
+    //   %Y = COPY %vregX
+    // =>
+    //   %Y = def
+    //   ...
+    if (!MRI->hasOneNonDBGUse(SrcReg)) {
       DEBUG(dbgs() << "\t\tMultiple vreg uses!\n");
       return false;
     }
 
-    MachineInstr *DestMI = MRI->getVRegDef(RHS.reg);
-    CopyMI = &*MRI->use_instr_nodbg_begin(RHS.reg);
-    const SlotIndex CopyRegIdx = LIS->getInstructionIndex(*CopyMI).getRegSlot();
-    const SlotIndex DestRegIdx = LIS->getInstructionIndex(*DestMI).getRegSlot();
+    MachineInstr &DestMI = *MRI->getVRegDef(SrcReg);
+    CopyMI = &*MRI->use_instr_nodbg_begin(SrcReg);
+    SlotIndex CopyRegIdx = LIS->getInstructionIndex(*CopyMI).getRegSlot();
+    SlotIndex DestRegIdx = LIS->getInstructionIndex(DestMI).getRegSlot();
 
     if (!MRI->isConstantPhysReg(DstReg)) {
       // We checked above that there are no interfering defs of the physical
@@ -1817,8 +1832,8 @@ bool RegisterCoalescer::joinReservedPhysReg(CoalescerPair &CP) {
 
     // We're going to remove the copy which defines a physical reserved
     // register, so remove its valno, etc.
-    DEBUG(dbgs() << "\t\tRemoving phys reg def of " << DstReg << " at "
-          << CopyRegIdx << "\n");
+    DEBUG(dbgs() << "\t\tRemoving phys reg def of " << PrintReg(DstReg, TRI)
+          << " at " << CopyRegIdx << "\n");
 
     LIS->removePhysRegDefAt(DstReg, CopyRegIdx);
     // Create a new dead def at the new def location.