Handle critical loop predecessors by making both inside and outside registers

live out.

This doesn't prevent us from inserting a loop preheader later on, if that is
better.

llvm-svn: 117424

2 files changed, 19 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/SplitKit.cpp b/llvm/lib/CodeGen/SplitKit.cpp
index cf297568f6d..a89a977695f 100644
--- a/llvm/lib/CodeGen/SplitKit.cpp
+++ b/llvm/lib/CodeGen/SplitKit.cpp
@@ -512,7 +512,7 @@ VNInfo *LiveIntervalMap::mapValue(const VNInfo *ParentVNI, SlotIndex Idx,
 // extendTo - Find the last li_ value defined in MBB at or before Idx. The
 // parentli_ is assumed to be live at Idx. Extend the live range to Idx.
 // Return the found VNInfo, or NULL.
-VNInfo *LiveIntervalMap::extendTo(MachineBasicBlock *MBB, SlotIndex Idx) {
+VNInfo *LiveIntervalMap::extendTo(const MachineBasicBlock *MBB, SlotIndex Idx) {
   assert(li_ && "call reset first");
   LiveInterval::iterator I = std::upper_bound(li_->begin(), li_->end(), Idx);
   if (I == li_->begin())
@@ -861,6 +861,16 @@ void SplitEditor::computeRemainder() {
       dupli_.addSimpleRange(LR.start, LR.end, LR.valno);
     }
   }
+
+  // Extend dupli_ to be live out of any critical loop predecessors.
+  // This means we have multiple registers live out of those blocks.
+  // The alternative would be to split the critical edges.
+  if (criticalPreds_.empty())
+    return;
+  for (SplitAnalysis::BlockPtrSet::iterator I = criticalPreds_.begin(),
+       E = criticalPreds_.end(); I != E; ++I)
+     dupli_.extendTo(*I, lis_.getMBBEndIdx(*I).getPrevSlot());
+   criticalPreds_.clear();
 }
 
 void SplitEditor::finish() {
@@ -924,6 +934,9 @@ void SplitEditor::splitAroundLoop(const MachineLoop *Loop) {
   sa_.getCriticalExits(Blocks, CriticalExits);
   assert(CriticalExits.empty() && "Cannot break critical exits yet");
 
+  // Get critical predecessors so computeRemainder can deal with them.
+  sa_.getCriticalPreds(Blocks, criticalPreds_);
+
   // Create new live interval for the loop.
   openIntv();
 
diff --git a/llvm/lib/CodeGen/SplitKit.h b/llvm/lib/CodeGen/SplitKit.h
index 08fac7f451d..9c109dc4d5f 100644
--- a/llvm/lib/CodeGen/SplitKit.h
+++ b/llvm/lib/CodeGen/SplitKit.h
@@ -200,7 +200,7 @@ public:
   // extendTo - Find the last li_ value defined in MBB at or before Idx. The
   // parentli is assumed to be live at Idx. Extend the live range to include
   // Idx. Return the found VNInfo, or NULL.
-  VNInfo *extendTo(MachineBasicBlock *MBB, SlotIndex Idx);
+  VNInfo *extendTo(const MachineBasicBlock *MBB, SlotIndex Idx);
 
   /// isMapped - Return true is ParentVNI is a known mapped value. It may be a
   /// simple 1-1 mapping or a complex mapping to later defs.
@@ -271,6 +271,10 @@ class SplitEditor {
   /// truncating any overlap with intervals_.
   void addTruncSimpleRange(SlotIndex Start, SlotIndex End, VNInfo *VNI);
 
+  /// criticalPreds_ - Set of basic blocks where both dupli and openli should be
+  /// live out because of a critical edge.
+  SplitAnalysis::BlockPtrSet criticalPreds_;
+
   /// computeRemainder - Compute the dupli liveness as the complement of all the
   /// new intervals.
   void computeRemainder();