[llvm] 7c03872 - LIS: fix handleMove to properly extend main range

[Stanislav Mekhanoshin via llvm-commits]

Author: Stanislav Mekhanoshin
Date: 2020-07-07T11:52:32-07:00
New Revision: 7c038726453b76d6f40590b22304c43ffa05aaf1

URL: https://github.com/llvm/llvm-project/commit/7c038726453b76d6f40590b22304c43ffa05aaf1
DIFF: https://github.com/llvm/llvm-project/commit/7c038726453b76d6f40590b22304c43ffa05aaf1.diff

LOG: LIS: fix handleMove to properly extend main range

handleMoveDown or handleMoveUp cannot properly repair a main
range of a LiveInterval since they only get LiveRange. There
is a problem if certain use has moved few segments away and
there is a hole in the main range in between of these two
locations. We may get a SubRange with a very extended Segment
spanning several Segments of the main range and also spanning
that hole. If that happens then we end up with the main range
not covering its SubRange which is an error.

It might be possible to attempt fixing the main range in place
just between of the old and new index by extending all of its
Segments in between, but it is unclear this logic will be
faster than just straight constructMainRangeFromSubranges,
which itself is pretty cheap since it only contains interval
logic. That will also require shrinkToUses() call after which
is probably even more expensive.

In the test second move is from 64B to 92B for the sub1.
Subrange is correctly fixed:

L000000000000000C [16r,32B:0)[32B,92r:1)  0 at 16r 1 at 32B-phi

But the main range has a hole in between 80d and 88r after
updateRange():

%1 [16r,32B:0)[32B,80r:4)[80r,80d:3)[88r,96r:1)[96r,160B:2)

Since source position is 64B this segment is not even considered
by the updateRange().

Differential Revision: https://reviews.llvm.org/D82916

Added: 
    

Modified: 
    llvm/lib/CodeGen/LiveIntervals.cpp
    llvm/unittests/MI/LiveIntervalTest.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/CodeGen/LiveIntervals.cpp b/llvm/lib/CodeGen/LiveIntervals.cpp
index 2bbe036e8425..e8ee0599e1a2 100644
--- a/llvm/lib/CodeGen/LiveIntervals.cpp
+++ b/llvm/lib/CodeGen/LiveIntervals.cpp
@@ -1011,6 +1011,20 @@ class LiveIntervals::HMEditor {
           }
         }
         updateRange(LI, Reg, LaneBitmask::getNone());
+        // If main range has a hole and we are moving a subrange use across
+        // the hole updateRange() cannot properly handle it since it only
+        // gets the LiveRange and not the whole LiveInterval. As a result
+        // we may end up with a main range not covering all subranges.
+        // This is extremely rare case, so let's check and reconstruct the
+        // main range.
+        for (LiveInterval::SubRange &S : LI.subranges()) {
+          if (LI.covers(S))
+            continue;
+          LI.clear();
+          LIS.constructMainRangeFromSubranges(LI);
+          break;
+        }
+
         continue;
       }
 

diff  --git a/llvm/unittests/MI/LiveIntervalTest.cpp b/llvm/unittests/MI/LiveIntervalTest.cpp
index 5c974ea7461e..3971d86e82d3 100644
--- a/llvm/unittests/MI/LiveIntervalTest.cpp
+++ b/llvm/unittests/MI/LiveIntervalTest.cpp
@@ -499,6 +499,26 @@ TEST(LiveIntervalTest, TestMoveSubRegDefAcrossUseDefMulti) {
   });
 }
 
+TEST(LiveIntervalTest, TestMoveSubRegUseAcrossMainRangeHole) {
+  liveIntervalTest(R"MIR(
+    %1:sgpr_128 = IMPLICIT_DEF
+  bb.1:
+    %2:sgpr_32 = COPY %1.sub2
+    %3:sgpr_32 = COPY %1.sub1
+    %1.sub2 = COPY %2
+    undef %1.sub0 = IMPLICIT_DEF
+    %1.sub2 = IMPLICIT_DEF
+    S_CBRANCH_SCC1 %bb.1, implicit undef $scc
+    S_BRANCH %bb.2
+  bb.2:
+)MIR", [](MachineFunction &MF, LiveIntervals &LIS) {
+    MachineInstr &MI = getMI(MF, 3, /*BlockNum=*/1);
+    MI.getOperand(0).setIsUndef(false);
+    testHandleMove(MF, LIS, 4, 3, 1);
+    testHandleMove(MF, LIS, 1, 4, 1);
+  });
+}
+
 TEST(LiveIntervalTest, BundleUse) {
   liveIntervalTest(R"MIR(
     %0 = IMPLICIT_DEF