Minimize the slot indexes spanned by register ranges created when splitting.

When an interfering live range ends at a dead slot index between two
instructions, make sure that the inserted copy instruction gets a slot index
after the dead ones. This makes it possible to avoid the interference.

Ideally, there shouldn't be interference ending at a deleted instruction, but
physical register coalescing can sometimes do that to sub-registers.

This fixes PR9823.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@130687 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 13 insertions, 5 deletions

diff --git a/lib/CodeGen/LiveRangeEdit.cpp b/lib/CodeGen/LiveRangeEdit.cpp
index 443cc2e904..f8a3dbb5fd 100644
--- a/lib/CodeGen/LiveRangeEdit.cpp
+++ b/lib/CodeGen/LiveRangeEdit.cpp
@@ -140,11 +140,13 @@ SlotIndex LiveRangeEdit::rematerializeAt(MachineBasicBlock &MBB,
                                          const Remat &RM,
                                          LiveIntervals &lis,
                                          const TargetInstrInfo &tii,
-                                         const TargetRegisterInfo &tri) {
+                                         const TargetRegisterInfo &tri,
+                                         bool Late) {
   assert(RM.OrigMI && "Invalid remat");
   tii.reMaterialize(MBB, MI, DestReg, 0, RM.OrigMI, tri);
   rematted_.insert(RM.ParentVNI);
-  return lis.InsertMachineInstrInMaps(--MI).getDefIndex();
+  return lis.getSlotIndexes()->insertMachineInstrInMaps(--MI, Late)
+           .getDefIndex();
 }
 
 void LiveRangeEdit::eraseVirtReg(unsigned Reg, LiveIntervals &LIS) {
diff --git a/lib/CodeGen/LiveRangeEdit.h b/lib/CodeGen/LiveRangeEdit.h
index c008d7647d..14d227e619 100644
--- a/lib/CodeGen/LiveRangeEdit.h
+++ b/lib/CodeGen/LiveRangeEdit.h
@@ -165,7 +165,8 @@ public:
                             const Remat &RM,
                             LiveIntervals&,
                             const TargetInstrInfo&,
-                            const TargetRegisterInfo&);
+                            const TargetRegisterInfo&,
+                            bool Late = false);
 
   /// markRematerialized - explicitly mark a value as rematerialized after doing
   /// it manually.
diff --git a/lib/CodeGen/SplitKit.cpp b/lib/CodeGen/SplitKit.cpp
index 427ef94ad7..ac9d72bf62 100644
--- a/lib/CodeGen/SplitKit.cpp
+++ b/lib/CodeGen/SplitKit.cpp
@@ -579,15 +579,20 @@ VNInfo *SplitEditor::defFromParent(unsigned RegIdx,
   SlotIndex Def;
   LiveInterval *LI = Edit->get(RegIdx);
 
+  // We may be trying to avoid interference that ends at a deleted instruction,
+  // so always begin RegIdx 0 early and all others late.
+  bool Late = RegIdx != 0;
+
   // Attempt cheap-as-a-copy rematerialization.
   LiveRangeEdit::Remat RM(ParentVNI);
   if (Edit->canRematerializeAt(RM, UseIdx, true, LIS)) {
-    Def = Edit->rematerializeAt(MBB, I, LI->reg, RM, LIS, TII, TRI);
+    Def = Edit->rematerializeAt(MBB, I, LI->reg, RM, LIS, TII, TRI, Late);
   } else {
     // Can't remat, just insert a copy from parent.
     CopyMI = BuildMI(MBB, I, DebugLoc(), TII.get(TargetOpcode::COPY), LI->reg)
                .addReg(Edit->getReg());
-    Def = LIS.InsertMachineInstrInMaps(CopyMI).getDefIndex();
+    Def = LIS.getSlotIndexes()->insertMachineInstrInMaps(CopyMI, Late)
+            .getDefIndex();
   }
 
   // Define the value in Reg.