Auto-compute live intervals on demand.

When new virtual registers are created during splitting/spilling, defer
creation of the live interval until we need to use the live interval.

Along with the recent commits to notify LiveRangeEdit when new virtual
registers are created, this makes it possible for functions like
TargetInstrInfo::loadRegFromStackSlot() and
TargetInstrInfo::storeRegToStackSlot() to create multiple virtual
registers as part of the process of generating loads/stores for
different register classes, and then have the live intervals for those
new registers computed when they are needed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188437 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 11 insertions, 3 deletions

diff --git a/lib/CodeGen/LiveRangeEdit.cpp b/lib/CodeGen/LiveRangeEdit.cpp
index 04f92adefd..ca64729ab9 100644
--- a/lib/CodeGen/LiveRangeEdit.cpp
+++ b/lib/CodeGen/LiveRangeEdit.cpp
@@ -30,15 +30,23 @@ STATISTIC(NumFracRanges,     "Number of live ranges fractured by DCE");
 
 void LiveRangeEdit::Delegate::anchor() { }
 
-LiveInterval &LiveRangeEdit::createFrom(unsigned OldReg) {
+LiveInterval &LiveRangeEdit::createEmptyIntervalFrom(unsigned OldReg) {
   unsigned VReg = MRI.createVirtualRegister(MRI.getRegClass(OldReg));
   if (VRM) {
     VRM->setIsSplitFromReg(VReg, VRM->getOriginal(OldReg));
   }
-  LiveInterval &LI = LIS.getOrCreateInterval(VReg);
+  LiveInterval &LI = LIS.createEmptyInterval(VReg);
   return LI;
 }
 
+unsigned LiveRangeEdit::createFrom(unsigned OldReg) {
+  unsigned VReg = MRI.createVirtualRegister(MRI.getRegClass(OldReg));
+  if (VRM) {
+    VRM->setIsSplitFromReg(VReg, VRM->getOriginal(OldReg));
+  }
+  return VReg;
+}
+
 bool LiveRangeEdit::checkRematerializable(VNInfo *VNI,
                                           const MachineInstr *DefMI,
                                           AliasAnalysis *aa) {
@@ -368,7 +376,7 @@ void LiveRangeEdit::eliminateDeadDefs(SmallVectorImpl<MachineInstr*> &Dead,
     DEBUG(dbgs() << NumComp << " components: " << *LI << '\n');
     SmallVector<LiveInterval*, 8> Dups(1, LI);
     for (unsigned i = 1; i != NumComp; ++i) {
-      Dups.push_back(&createFrom(LI->reg));
+      Dups.push_back(&createEmptyIntervalFrom(LI->reg));
       // If LI is an original interval that hasn't been split yet, make the new
       // intervals their own originals instead of referring to LI. The original
       // interval must contain all the split products, and LI doesn't.