[llvm] [CodeGen] Introduce MI flag for Live Range split instructions (PR #117543)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-regalloc

Author: Christudasan Devadasan (cdevadas)

<details>
<summary>Changes</summary>

For some targets, it is required to identify the COPY instruction
corresponds to the RA inserted live range split. Adding the new
flag `MachineInstr::LRSplit` to serve the purpose.

---
Full diff: https://github.com/llvm/llvm-project/pull/117543.diff


2 Files Affected:

- (modified) llvm/include/llvm/CodeGen/MachineInstr.h (+2-1) 
- (modified) llvm/lib/CodeGen/SplitKit.cpp (+2) 


``````````diff
diff --git a/llvm/include/llvm/CodeGen/MachineInstr.h b/llvm/include/llvm/CodeGen/MachineInstr.h
index ead6bbe1d5f641..4545b205d07466 100644
--- a/llvm/include/llvm/CodeGen/MachineInstr.h
+++ b/llvm/include/llvm/CodeGen/MachineInstr.h
@@ -119,7 +119,8 @@ class MachineInstr
     Disjoint = 1 << 19,      // Each bit is zero in at least one of the inputs.
     NoUSWrap = 1 << 20,      // Instruction supports geps
                              // no unsigned signed wrap.
-    SameSign = 1 << 21       // Both operands have the same sign.
+    SameSign = 1 << 21,      // Both operands have the same sign.
+    LRSplit = 1 << 22        // Instruction for live range split.
   };
 
 private:
diff --git a/llvm/lib/CodeGen/SplitKit.cpp b/llvm/lib/CodeGen/SplitKit.cpp
index eb33b93c197d7c..5042f074c26c45 100644
--- a/llvm/lib/CodeGen/SplitKit.cpp
+++ b/llvm/lib/CodeGen/SplitKit.cpp
@@ -533,6 +533,7 @@ SlotIndex SplitEditor::buildSingleSubRegCopy(
               | getInternalReadRegState(!FirstCopy), SubIdx)
       .addReg(FromReg, 0, SubIdx);
 
+  CopyMI->setFlag(MachineInstr::LRSplit);
   SlotIndexes &Indexes = *LIS.getSlotIndexes();
   if (FirstCopy) {
     Def = Indexes.insertMachineInstrInMaps(*CopyMI, Late).getRegSlot();
@@ -552,6 +553,7 @@ SlotIndex SplitEditor::buildCopy(Register FromReg, Register ToReg,
     // The full vreg is copied.
     MachineInstr *CopyMI =
         BuildMI(MBB, InsertBefore, DebugLoc(), Desc, ToReg).addReg(FromReg);
+    CopyMI->setFlag(MachineInstr::LRSplit);
     return Indexes.insertMachineInstrInMaps(*CopyMI, Late).getRegSlot();
   }
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/117543