[llvm] [TwoAddressInstruction][NPM] Conditionally preserve SlotIndexes in NPM (PR #173536)

[Teja Alaghari via llvm-commits]

https://github.com/TejaX-Alaghari updated https://github.com/llvm/llvm-project/pull/173536

>From 2ee527df3d681487a107acb65b32d2e0c314e76b Mon Sep 17 00:00:00 2001
From: Teja Alaghari <teja.alaghari at amd.com>
Date: Thu, 25 Dec 2025 14:37:42 +0530
Subject: [PATCH] Conditionally preserve SlotIndexes in NPM

---
 .../lib/CodeGen/TwoAddressInstructionPass.cpp | 22 +++++++++++++------
 1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/llvm/lib/CodeGen/TwoAddressInstructionPass.cpp b/llvm/lib/CodeGen/TwoAddressInstructionPass.cpp
index dbad06623754c..9669b2bf018ff 100644
--- a/llvm/lib/CodeGen/TwoAddressInstructionPass.cpp
+++ b/llvm/lib/CodeGen/TwoAddressInstructionPass.cpp
@@ -190,7 +190,8 @@ class TwoAddressInstructionImpl {
 public:
   TwoAddressInstructionImpl(MachineFunction &MF, MachineFunctionPass *P);
   TwoAddressInstructionImpl(MachineFunction &MF,
-                            MachineFunctionAnalysisManager &MFAM);
+                            MachineFunctionAnalysisManager &MFAM,
+                            LiveIntervals *LIS);
   void setOptLevel(CodeGenOptLevel Level) { OptLevel = Level; }
   bool run();
 };
@@ -233,7 +234,9 @@ TwoAddressInstructionPass::run(MachineFunction &MF,
                                MachineFunctionAnalysisManager &MFAM) {
   // Disable optimizations if requested. We cannot skip the whole pass as some
   // fixups are necessary for correctness.
-  TwoAddressInstructionImpl Impl(MF, MFAM);
+  LiveIntervals *LIS = MFAM.getCachedResult<LiveIntervalsAnalysis>(MF);
+
+  TwoAddressInstructionImpl Impl(MF, MFAM, LIS);
   if (MF.getFunction().hasOptNone())
     Impl.setOptLevel(CodeGenOptLevel::None);
 
@@ -242,11 +245,16 @@ TwoAddressInstructionPass::run(MachineFunction &MF,
   if (!Changed)
     return PreservedAnalyses::all();
   auto PA = getMachineFunctionPassPreservedAnalyses();
-  PA.preserve<LiveIntervalsAnalysis>();
+
+  // SlotIndexes are only maintained when LiveIntervals is available. Only
+  // preserve SlotIndexes if we had LiveIntervals available and updated them.
+  if (LIS)
+    PA.preserve<SlotIndexesAnalysis>();
+
   PA.preserve<LiveVariablesAnalysis>();
+  PA.preserve<LiveIntervalsAnalysis>();
   PA.preserve<MachineDominatorTreeAnalysis>();
   PA.preserve<MachineLoopAnalysis>();
-  PA.preserve<SlotIndexesAnalysis>();
   PA.preserveSet<CFGAnalyses>();
   return PA;
 }
@@ -259,13 +267,13 @@ INITIALIZE_PASS(TwoAddressInstructionLegacyPass, DEBUG_TYPE,
                 "Two-Address instruction pass", false, false)
 
 TwoAddressInstructionImpl::TwoAddressInstructionImpl(
-    MachineFunction &Func, MachineFunctionAnalysisManager &MFAM)
+    MachineFunction &Func, MachineFunctionAnalysisManager &MFAM,
+    LiveIntervals *LIS)
     : MF(&Func), TII(Func.getSubtarget().getInstrInfo()),
       TRI(Func.getSubtarget().getRegisterInfo()),
       InstrItins(Func.getSubtarget().getInstrItineraryData()),
       MRI(&Func.getRegInfo()),
-      LV(MFAM.getCachedResult<LiveVariablesAnalysis>(Func)),
-      LIS(MFAM.getCachedResult<LiveIntervalsAnalysis>(Func)),
+      LV(MFAM.getCachedResult<LiveVariablesAnalysis>(Func)), LIS(LIS),
       OptLevel(Func.getTarget().getOptLevel()) {}
 
 TwoAddressInstructionImpl::TwoAddressInstructionImpl(MachineFunction &Func,