PR11868. The previous loop in LiveIntervals::join would sometimes fall over if

more than two adjacent ranges needed to be merged. The new version should be
able to handle an arbitrary sequence of adjancent ranges.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@149588 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 12 insertions, 11 deletions

diff --git a/lib/CodeGen/LiveInterval.cpp b/lib/CodeGen/LiveInterval.cpp
index a85639f9c1..0dbaaf804b 100644
--- a/lib/CodeGen/LiveInterval.cpp
+++ b/lib/CodeGen/LiveInterval.cpp
@@ -389,29 +389,30 @@ void LiveInterval::join(LiveInterval &Other,
   // now.
   if (MustMapCurValNos) {
     // Map the first live range.
+
     iterator OutIt = begin();
     OutIt->valno = NewVNInfo[LHSValNoAssignments[OutIt->valno->id]];
-    ++OutIt;
-    for (iterator I = OutIt, E = end(); I != E; ++I) {
-      OutIt->valno = NewVNInfo[LHSValNoAssignments[I->valno->id]];
+    for (iterator I = next(OutIt), E = end(); I != E; ++I) {
+      VNInfo* nextValNo = NewVNInfo[LHSValNoAssignments[I->valno->id]];
+      assert(nextValNo != 0 && "Huh?");
 
       // If this live range has the same value # as its immediate predecessor,
       // and if they are neighbors, remove one LiveRange.  This happens when we
-      // have [0,3:0)[4,7:1) and map 0/1 onto the same value #.
-      if (OutIt->valno == (OutIt-1)->valno && (OutIt-1)->end == OutIt->start) {
-        (OutIt-1)->end = OutIt->end;
+      // have [0,4:0)[4,7:1) and map 0/1 onto the same value #.
+      if (OutIt->valno == nextValNo && OutIt->end == I->start) {
+        OutIt->end = I->end;
       } else {
-        if (I != OutIt) {
+        // Didn't merge. Move OutIt to the next interval,
+        ++OutIt;
+        OutIt->valno = nextValNo;
+        if (OutIt != I) {
           OutIt->start = I->start;
           OutIt->end = I->end;
         }
-
-        // Didn't merge, on to the next one.
-        ++OutIt;
       }
     }
-
     // If we merge some live ranges, chop off the end.
+    ++OutIt;
     ranges.erase(OutIt, end());
   }