Insert two blank SlotIndexes between basic blocks instead of just one.

This is the first small step towards using closed intervals for liveness instead
of the half-open intervals we're using now.

We want to be able to distinguish between a SlotIndex that represents a variable
being live-out of a basic block, and an index representing a variable live-in to
its successor.

That requires two separate indexes between blocks. One for live-outs and one for
live-ins.

With this change, getMBBEndIdx(MBB).getPrevSlot() becomes stable so it stays
greater than any instructions inserted at the end of MBB.

llvm-svn: 118747

1 files changed, 6 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/SlotIndexes.cpp b/llvm/lib/CodeGen/SlotIndexes.cpp
index adab9ff3a5a..277cce3db88 100644
--- a/llvm/lib/CodeGen/SlotIndexes.cpp
+++ b/llvm/lib/CodeGen/SlotIndexes.cpp
@@ -127,8 +127,12 @@ bool SlotIndexes::runOnMachineFunction(MachineFunction &fn) {
       index += (Slots + 1) * SlotIndex::NUM;
     }
 
-    // One blank instruction at the end.
-    push_back(createEntry(0, index));    
+    // We insert two blank instructions between basic blocks.
+    // One to represent live-out registers and one to represent live-ins.
+    push_back(createEntry(0, index));
+    index += SlotIndex::NUM;
+
+    push_back(createEntry(0, index));
 
     SlotIndex blockEndIndex(back(), SlotIndex::LOAD);
     mbb2IdxMap.insert(