Rewrite RAGreedy::splitAroundRegion, now with cool ASCII art.

This function has to deal with a lot of special cases, and the old
version got it wrong sometimes. In particular, it would sometimes leave
multiple uses in the stack interval in a single block. That causes bad
code with multiple reloads in the same basic block.

The new version handles block entry and exit in a single pass. It first
eliminates all the easy cases, and then goes on to create a local
interval for the blocks with difficult interference. Previously, we
would only create the local interval for completely isolated blocks.

It can happen that the stack interval becomes completely empty because
we could allocate a register in all edge bundles, and the new local
intervals deal with the interference. The empty stack interval is
harmless, but we need to remove a SplitKit assertion that checks for
empty intervals.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@134047 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 10 insertions, 0 deletions

diff --git a/lib/CodeGen/SplitKit.h b/lib/CodeGen/SplitKit.h
index 7174c0b55f..a9ccf40be2 100644
--- a/lib/CodeGen/SplitKit.h
+++ b/lib/CodeGen/SplitKit.h
@@ -81,6 +81,12 @@ public:
     bool LiveThrough;     ///< Live in whole block (Templ 5. above).
     bool LiveIn;          ///< Current reg is live in.
     bool LiveOut;         ///< Current reg is live out.
+
+    /// isOneInstr - Returns true when this BlockInfo describes a single
+    /// instruction.
+    bool isOneInstr() const {
+      return SlotIndex::isSameInstr(FirstUse, LastUse);
+    }
   };
 
 private:
@@ -360,6 +366,10 @@ public:
   /// Return the beginning of the new live range.
   SlotIndex enterIntvBefore(SlotIndex Idx);
 
+  /// enterIntvAfter - Enter the open interval after the instruction at Idx.
+  /// Return the beginning of the new live range.
+  SlotIndex enterIntvAfter(SlotIndex Idx);
+
   /// enterIntvAtEnd - Enter the open interval at the end of MBB.
   /// Use the open interval from he inserted copy to the MBB end.
   /// Return the beginning of the new live range.