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, 9 insertions, 2 deletions

diff --git a/include/llvm/CodeGen/LiveRangeEdit.h b/include/llvm/CodeGen/LiveRangeEdit.h
index 43a9566..7edf67c 100644
--- a/include/llvm/CodeGen/LiveRangeEdit.h
+++ b/include/llvm/CodeGen/LiveRangeEdit.h
@@ -144,12 +144,19 @@ public:
     return makeArrayRef(NewRegs).slice(FirstNew);
   }
 
+  /// createEmptyIntervalFrom - Create a new empty interval based on OldReg.
+  LiveInterval &createEmptyIntervalFrom(unsigned OldReg);
+
   /// createFrom - Create a new virtual register based on OldReg.
-  LiveInterval &createFrom(unsigned OldReg);
+  unsigned createFrom(unsigned OldReg);
 
   /// create - Create a new register with the same class and original slot as
   /// parent.
-  LiveInterval &create() {
+  LiveInterval &createEmptyInterval() {
+    return createEmptyIntervalFrom(getReg());
+  }
+
+  unsigned create() {
     return createFrom(getReg());
   }