Gracefully handle invalid live ranges. Fix PR9831.

Register coalescing can sometimes create live ranges that end in the middle of a
basic block without any killing instruction. When SplitKit detects this, it will
repair the live range by shrinking it to its uses.

Live range splitting also needs to know about this. When the range shrinks so
much that it becomes allocatable, live range splitting fails because it can't
find a good split point. It is paranoid about making progress, so an allocatable
range is considered an error.

The coalescer should really not be creating these bad live ranges. They appear
when coalescing dead copies.

llvm-svn: 130787

1 files changed, 2 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SplitKit.cpp b/llvm/lib/CodeGen/SplitKit.cpp
index ac9d72bf62c..feb3d3481b4 100644
--- a/llvm/lib/CodeGen/SplitKit.cpp
+++ b/llvm/lib/CodeGen/SplitKit.cpp
@@ -51,6 +51,7 @@ void SplitAnalysis::clear() {
   UseBlocks.clear();
   ThroughBlocks.clear();
   CurLI = 0;
+  DidRepairRange = false;
 }
 
 SlotIndex SplitAnalysis::computeLastSplitPoint(unsigned Num) {
@@ -119,6 +120,7 @@ void SplitAnalysis::analyzeUses() {
   if (!calcLiveBlockInfo()) {
     // FIXME: calcLiveBlockInfo found inconsistencies in the live range.
     // I am looking at you, SimpleRegisterCoalescing!
+    DidRepairRange = true;
     DEBUG(dbgs() << "*** Fixing inconsistent live interval! ***\n");
     const_cast<LiveIntervals&>(LIS)
       .shrinkToUses(const_cast<LiveInterval*>(CurLI));