Don't use pointer-pointers for the register use lists.

Use a more conventional doubly linked list where the Prev pointers form
a cycle. This means it is no longer necessary to adjust the Prev
pointers when reallocating the VRegInfo array.

The test changes are required because the register allocation hint is
using the use-list order to break ties.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@161633 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 39 insertions, 45 deletions

diff --git a/lib/CodeGen/MachineRegisterInfo.cpp b/lib/CodeGen/MachineRegisterInfo.cpp
index 6d05d35d7a..bd826fb7c1 100644
--- a/lib/CodeGen/MachineRegisterInfo.cpp
+++ b/lib/CodeGen/MachineRegisterInfo.cpp
@@ -102,17 +102,9 @@ MachineRegisterInfo::createVirtualRegister(const TargetRegisterClass *RegClass){
 
   // New virtual register number.
   unsigned Reg = TargetRegisterInfo::index2VirtReg(getNumVirtRegs());
-
-  // Add a reg, but keep track of whether the vector reallocated or not.
-  const unsigned FirstVirtReg = TargetRegisterInfo::index2VirtReg(0);
-  void *ArrayBase = getNumVirtRegs() == 0 ? 0 : &VRegInfo[FirstVirtReg];
   VRegInfo.grow(Reg);
   VRegInfo[Reg].first = RegClass;
   RegAllocHints.grow(Reg);
-
-  if (ArrayBase && &VRegInfo[FirstVirtReg] != ArrayBase)
-    // The vector reallocated, handle this now.
-    HandleVRegListReallocation();
   return Reg;
 }
 
@@ -129,55 +121,57 @@ void MachineRegisterInfo::clearVirtRegs() {
 /// Add MO to the linked list of operands for its register.
 void MachineRegisterInfo::addRegOperandToUseList(MachineOperand *MO) {
   assert(!MO->isOnRegUseList() && "Already on list");
-  MachineOperand **Head = &getRegUseDefListHead(MO->getReg());
-
-  // For SSA values, we prefer to keep the definition at the start of the list.
-  // we do this by skipping over the definition if it is at the head of the
-  // list.
-  if (*Head && (*Head)->isDef())
-    Head = &(*Head)->Contents.Reg.Next;
-
-  MO->Contents.Reg.Next = *Head;
-  if (MO->Contents.Reg.Next) {
-    assert(MO->getReg() == MO->Contents.Reg.Next->getReg() &&
-           "Different regs on the same list!");
-    MO->Contents.Reg.Next->Contents.Reg.Prev = &MO->Contents.Reg.Next;
+  MachineOperand *&HeadRef = getRegUseDefListHead(MO->getReg());
+  MachineOperand *const Head = HeadRef;
+
+  // Head points to the first list element.
+  // Next is NULL on the last list element.
+  // Prev pointers are circular, so Head->Prev == Last.
+
+  // Head is NULL for an empty list.
+  if (!Head) {
+    MO->Contents.Reg.Prev = MO;
+    MO->Contents.Reg.Next = 0;
+    HeadRef = MO;
+    return;
   }
-
-  MO->Contents.Reg.Prev = Head;
-  *Head = MO;
+  assert(MO->getReg() == Head->getReg() && "Different regs on the same list!");
+
+  // Insert MO between Last and Head in the circular Prev chain.
+  MachineOperand *Last = Head->Contents.Reg.Prev;
+  assert(Last && "Inconsistent use list");
+  assert(MO->getReg() == Last->getReg() && "Different regs on the same list!");
+  Head->Contents.Reg.Prev = MO;
+  MO->Contents.Reg.Prev = Last;
+
+  // Insert at the front.
+  MO->Contents.Reg.Next = Head;
+  HeadRef = MO;
 }
 
 /// Remove MO from its use-def list.
 void MachineRegisterInfo::removeRegOperandFromUseList(MachineOperand *MO) {
   assert(MO->isOnRegUseList() && "Operand not on use list");
+  MachineOperand *&HeadRef = getRegUseDefListHead(MO->getReg());
+  MachineOperand *const Head = HeadRef;
+  assert(Head && "List already empty");
 
   // Unlink this from the doubly linked list of operands.
-  MachineOperand *NextOp = MO->Contents.Reg.Next;
-  *MO->Contents.Reg.Prev = NextOp;
-  if (NextOp) {
-    assert(NextOp->getReg() == MO->getReg() && "Corrupt reg use/def chain!");
-    NextOp->Contents.Reg.Prev = MO->Contents.Reg.Prev;
-  }
+  MachineOperand *Next = MO->Contents.Reg.Next;
+  MachineOperand *Prev = MO->Contents.Reg.Prev;
+
+  // Prev links are circular, next link is NULL instead of looping back to Head.
+  if (MO == Head)
+    HeadRef = Next;
+  else
+    Prev->Contents.Reg.Next = Next;
+
+  (Next ? Next : Head)->Contents.Reg.Prev = Prev;
+
   MO->Contents.Reg.Prev = 0;
   MO->Contents.Reg.Next = 0;
 }
 
-/// HandleVRegListReallocation - We just added a virtual register to the
-/// VRegInfo info list and it reallocated.  Update the use/def lists info
-/// pointers.
-void MachineRegisterInfo::HandleVRegListReallocation() {
-  // The back pointers for the vreg lists point into the previous vector.
-  // Update them to point to their correct slots.
-  for (unsigned i = 0, e = getNumVirtRegs(); i != e; ++i) {
-    unsigned Reg = TargetRegisterInfo::index2VirtReg(i);
-    MachineOperand *List = VRegInfo[Reg].second;
-    if (!List) continue;
-    // Update the back-pointer to be accurate once more.
-    List->Contents.Reg.Prev = &VRegInfo[Reg].second;
-  }
-}
-
 /// replaceRegWith - Replace all instances of FromReg with ToReg in the
 /// machine function.  This is like llvm-level X->replaceAllUsesWith(Y),
 /// except that it also changes any definitions of the register as well.