More fixes for subreg join failure in RegCoalescer

Summary:
Part of the adjustCopiesBackFrom method wasn't correctly dealing with SubRange
intervals when updating.

2 changes. The first to ensure that bogus SubRange Segments aren't propagated when
encountering Segments of the form [1234r, 1234d:0) when preparing to merge value
numbers. These can be removed in this case.

The second forces a shrinkToUses call if SubRanges end on the copy index
(instead of just the parent register).

V2: Addressed review comments, plus MIR test instead of ll test

Subscribers: MatzeB, qcolombet, nhaehnle

Differential Revision: https://reviews.llvm.org/D40308

Change-Id: I1d2b2b4beea802fce11da01edf71feb2064aab05
llvm-svn: 337273

1 files changed, 21 insertions, 4 deletions

diff --git a/llvm/lib/CodeGen/RegisterCoalescer.cpp b/llvm/lib/CodeGen/RegisterCoalescer.cpp
index 02164d9afbe..5c5f8dc528c 100644
--- a/llvm/lib/CodeGen/RegisterCoalescer.cpp
+++ b/llvm/lib/CodeGen/RegisterCoalescer.cpp
@@ -589,6 +589,13 @@ bool RegisterCoalescer::adjustCopiesBackFrom(const CoalescerPair &CP,
 
   // Do the same for the subregister segments.
   for (LiveInterval::SubRange &S : IntB.subranges()) {
+    // Check for SubRange Segments of the form [1234r,1234d:0) which can be
+    // removed to prevent creating bogus SubRange Segments.
+    LiveInterval::iterator SS = S.FindSegmentContaining(CopyIdx);
+    if (SS != S.end() && SlotIndex::isSameInstr(SS->start, SS->end)) {
+      S.removeSegment(*SS, true);
+      continue;
+    }
     VNInfo *SubBValNo = S.getVNInfoAt(CopyIdx);
     S.addSegment(LiveInterval::Segment(FillerStart, FillerEnd, SubBValNo));
     VNInfo *SubValSNo = S.getVNInfoAt(AValNo->def.getPrevSlot());
@@ -605,11 +612,21 @@ bool RegisterCoalescer::adjustCopiesBackFrom(const CoalescerPair &CP,
     ValSEndInst->getOperand(UIdx).setIsKill(false);
   }
 
-  // Rewrite the copy. If the copy instruction was killing the destination
-  // register before the merge, find the last use and trim the live range. That
-  // will also add the isKill marker.
+  // Rewrite the copy.
   CopyMI->substituteRegister(IntA.reg, IntB.reg, 0, *TRI);
-  if (AS->end == CopyIdx)
+  // If the copy instruction was killing the destination register or any
+  // subrange before the merge trim the live range.
+  bool RecomputeLiveRange = AS->end == CopyIdx;
+  if (!RecomputeLiveRange) {
+    for (LiveInterval::SubRange &S : IntA.subranges()) {
+      LiveInterval::iterator SS = S.FindSegmentContaining(CopyUseIdx);
+      if (SS != S.end() && SS->end == CopyIdx) {
+        RecomputeLiveRange = true;
+        break;
+      }
+    }
+  }
+  if (RecomputeLiveRange)
     shrinkToUses(&IntA);
 
   ++numExtends;