Add MachineRegisterInfo::moveOperands().

This function works like memmove() for MachineOperands, except it also
updates any use-def chains containing the moved operands.

The use-def chains are updated without affecting the order of operands
in the list. That isn't possible when using the
removeRegOperandFromUseList() and addRegOperandToUseList() functions.

Callers to follow soon.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171597 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/MachineRegisterInfo.h

@@ -156,6 +156,9 @@ public:
   // Strictly for use by MachineInstr.cpp.
   void removeRegOperandFromUseList(MachineOperand *MO);
 
+  // Strictly for use by MachineInstr.cpp.
+  void moveOperands(MachineOperand *Dst, MachineOperand *Src, unsigned NumOps);
+
   /// reg_begin/reg_end - Provide iteration support to walk over all definitions
   /// and uses of a register within the MachineFunction that corresponds to this
   /// MachineRegisterInfo object.

lib/CodeGen/MachineRegisterInfo.cpp

@@ -180,6 +180,55 @@ void MachineRegisterInfo::removeRegOperandFromUseList(MachineOperand *MO) {
   MO->Contents.Reg.Next = 0;
 }
 
+/// Move NumOps operands from Src to Dst, updating use-def lists as needed.
+///
+/// The Dst range is assumed to be uninitialized memory. (Or it may contain
+/// operands that won't be destroyed, which is OK because the MO destructor is
+/// trivial anyway).
+///
+/// The Src and Dst ranges may overlap.
+void MachineRegisterInfo::moveOperands(MachineOperand *Dst,
+                                       MachineOperand *Src,
+                                       unsigned NumOps) {
+  assert(Src != Dst && NumOps && "Noop moveOperands");
+
+  // Copy backwards if Dst is within the Src range.
+  int Stride = 1;
+  if (Dst >= Src && Dst < Src + NumOps) {
+    Stride = -1;
+    Dst += NumOps - 1;
+    Src += NumOps - 1;
+  }
+
+  // Copy one operand at a time.
+  do {
+    new (Dst) MachineOperand(*Src);
+
+    // Dst takes Src's place in the use-def chain.
+    if (Src->isReg()) {
+      MachineOperand *&Head = getRegUseDefListHead(Src->getReg());
+      MachineOperand *Prev = Src->Contents.Reg.Prev;
+      MachineOperand *Next = Src->Contents.Reg.Next;
+      assert(Head && "List empty, but operand is chained");
+      assert(Prev && "Operand was not on use-def list");
+
+      // Prev links are circular, next link is NULL instead of looping back to
+      // Head.
+      if (Src == Head)
+        Head = Dst;
+      else
+        Prev->Contents.Reg.Next = Dst;
+
+      // Update Prev pointer. This also works when Src was pointing to itself
+      // in a 1-element list. In that case Head == Dst.
+      (Next ? Next : Head)->Contents.Reg.Prev = Dst;
+    }
+
+    Dst += Stride;
+    Src += Stride;
+  } while (--NumOps);
+}
+
 /// 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.