Add SplitEditor::overlapIntv() to create small ranges where both registers are live.

If a live range is used by a terminator instruction, and that live range needs
to leave the block on the stack or in a different register, it can be necessary
to have both sides of the split live at the terminator instruction.

Example:

  %vreg2 = COPY %vreg1
  JMP %vreg1

Becomes after spilling %vreg2:

  SPILL %vreg1
  JMP %vreg1

The spill doesn't kill the register as is normally the case.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@125102 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 16 insertions, 0 deletions

diff --git a/lib/CodeGen/SplitKit.cpp b/lib/CodeGen/SplitKit.cpp
index 0c2a2cf432..e26d909211 100644
--- a/lib/CodeGen/SplitKit.cpp
+++ b/lib/CodeGen/SplitKit.cpp
@@ -882,6 +882,22 @@ SlotIndex SplitEditor::leaveIntvAtTop(MachineBasicBlock &MBB) {
   return VNI->def;
 }
 
+void SplitEditor::overlapIntv(SlotIndex Start, SlotIndex End) {
+  assert(OpenIdx && "openIntv not called before overlapIntv");
+  assert(Edit.getParent().getVNInfoAt(Start) ==
+         Edit.getParent().getVNInfoAt(End.getPrevSlot()) &&
+         "Parent changes value in extended range");
+  assert(Edit.get(0)->getVNInfoAt(Start) && "Start must come from leaveIntv*");
+  assert(LIS.getMBBFromIndex(Start) == LIS.getMBBFromIndex(End) &&
+         "Range cannot span basic blocks");
+
+  // Treat this as useIntv() for now. The complement interval will be extended
+  // as needed by mapValue().
+  DEBUG(dbgs() << "    overlapIntv [" << Start << ';' << End << "):");
+  RegAssign.insert(Start, End, OpenIdx);
+  DEBUG(dump());
+}
+
 /// closeIntv - Indicate that we are done editing the currently open
 /// LiveInterval, and ranges can be trimmed.
 void SplitEditor::closeIntv() {