[LiveRange] Reset the VNIs when splitting subranges

When splitting a subrange we end up with two different subranges covering
two different, non overlapping, lanes.
As part of this splitting the VNIs of the original live-range need
to be dispatched to the subranges according to which lanes they are
actually defining.

Prior to this patch we were assuming that all values were defining
all lanes. This was wrong as demonstrated by llvm.org/PR40835.

Differential Revision: https://reviews.llvm.org/D59731

llvm-svn: 357032

1 files changed, 51 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/LiveInterval.cpp b/llvm/lib/CodeGen/LiveInterval.cpp
index 821680e756c..3dc030303a0 100644
--- a/llvm/lib/CodeGen/LiveInterval.cpp
+++ b/llvm/lib/CodeGen/LiveInterval.cpp
@@ -879,8 +879,53 @@ void LiveInterval::clearSubRanges() {
   SubRanges = nullptr;
 }
 
-void LiveInterval::refineSubRanges(BumpPtrAllocator &Allocator,
-    LaneBitmask LaneMask, std::function<void(LiveInterval::SubRange&)> Apply) {
+/// For each VNI in \p SR, check whether or not that value defines part
+/// of the mask describe by \p LaneMask and if not, remove that value
+/// from \p SR.
+static void stripValuesNotDefiningMask(unsigned Reg, LiveInterval::SubRange &SR,
+                                       LaneBitmask LaneMask,
+                                       const SlotIndexes &Indexes,
+                                       const TargetRegisterInfo &TRI) {
+  // Phys reg should not be tracked at subreg level.
+  // Same for noreg (Reg == 0).
+  if (!TargetRegisterInfo::isVirtualRegister(Reg) || !Reg)
+    return;
+  // Remove the values that don't define those lanes.
+  SmallVector<VNInfo *, 8> ToBeRemoved;
+  for (VNInfo *VNI : SR.valnos) {
+    if (VNI->isUnused())
+      continue;
+    // PHI definitions don't have MI attached, so there is nothing
+    // we can use to strip the VNI.
+    if (VNI->isPHIDef())
+      continue;
+    const MachineInstr *MI = Indexes.getInstructionFromIndex(VNI->def);
+    assert(MI && "Cannot find the definition of a value");
+    bool hasDef = false;
+    for (ConstMIBundleOperands MOI(*MI); MOI.isValid(); ++MOI) {
+      if (!MOI->isReg() || !MOI->isDef())
+        continue;
+      if (MOI->getReg() != Reg)
+        continue;
+      if ((TRI.getSubRegIndexLaneMask(MOI->getSubReg()) & LaneMask).none())
+        continue;
+      hasDef = true;
+      break;
+    }
+
+    if (!hasDef)
+      ToBeRemoved.push_back(VNI);
+  }
+  for (VNInfo *VNI : ToBeRemoved)
+    SR.removeValNo(VNI);
+
+  assert(!SR.empty() && "At least one value should be defined by this mask");
+}
+
+void LiveInterval::refineSubRanges(
+    BumpPtrAllocator &Allocator, LaneBitmask LaneMask,
+    std::function<void(LiveInterval::SubRange &)> Apply,
+    const SlotIndexes &Indexes, const TargetRegisterInfo &TRI) {
   LaneBitmask ToApply = LaneMask;
   for (SubRange &SR : subranges()) {
     LaneBitmask SRMask = SR.LaneMask;
@@ -898,6 +943,10 @@ void LiveInterval::refineSubRanges(BumpPtrAllocator &Allocator,
       SR.LaneMask = SRMask & ~Matching;
       // Create a new subrange for the matching part
       MatchingRange = createSubRangeFrom(Allocator, Matching, SR);
+      // Now that the subrange is split in half, make sure we
+      // only keep in the subranges the VNIs that touch the related half.
+      stripValuesNotDefiningMask(reg, *MatchingRange, Matching, Indexes, TRI);
+      stripValuesNotDefiningMask(reg, SR, SR.LaneMask, Indexes, TRI);
     }
     Apply(*MatchingRange);
     ToApply &= ~Matching;