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.

llvm-svn: 130687

1 files changed, 7 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/SplitKit.cpp b/llvm/lib/CodeGen/SplitKit.cpp
index 427ef94ad7d..ac9d72bf62c 100644
--- a/llvm/lib/CodeGen/SplitKit.cpp
+++ b/llvm/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.