Revert r161633-161634 "Partition use lists so defs always come before uses."

These commits broke a number of buildbots.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@161640 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 45 insertions, 47 deletions

diff --git a/lib/CodeGen/MachineRegisterInfo.cpp b/lib/CodeGen/MachineRegisterInfo.cpp
index 5fb938f..6d05d35 100644
--- a/lib/CodeGen/MachineRegisterInfo.cpp
+++ b/lib/CodeGen/MachineRegisterInfo.cpp
@@ -102,9 +102,17 @@ 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;
 }
 
@@ -121,65 +129,55 @@ 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 *&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;
-  }
-  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;
-
-  // Def operands always precede uses. This allows def_iterator to stop early.
-  // Insert def operands at the front, and use operands at the back.
-  if (MO->isDef()) {
-    // Insert def at the front.
-    MO->Contents.Reg.Next = Head;
-    HeadRef = MO;
-  } else {
-    // Insert use at the end.
-    MO->Contents.Reg.Next = 0;
-    Last->Contents.Reg.Next = MO;
+  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;
   }
+
+  MO->Contents.Reg.Prev = Head;
+  *Head = 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 *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;
-
+  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;
+  }
   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.