From 913ba8eeb414ae351d4e3c7930ec3401ba3dd364 Mon Sep 17 00:00:00 2001
From: Stanislav Mekhanoshin <Stanislav.Mekhanoshin@amd.com>
Date: Tue, 9 Apr 2019 16:13:53 +0000
Subject: Revert LIS handling in MachineDCE

One of out of tree targets has regressed with this patch. Reverting
it for now and let liveness to be fully reconstructed in case pass
was used after the LIS is created to resolve the regression.

Differential Revision: https://reviews.llvm.org/D60466

llvm-svn: 358015
---
 llvm/lib/CodeGen/DeadMachineInstructionElim.cpp | 30 ++-----------------------
 1 file changed, 2 insertions(+), 28 deletions(-)

(limited to 'llvm/lib/CodeGen/DeadMachineInstructionElim.cpp')

diff --git a/llvm/lib/CodeGen/DeadMachineInstructionElim.cpp b/llvm/lib/CodeGen/DeadMachineInstructionElim.cpp
index f1de7b3cc6a..049ce706330 100644
--- a/llvm/lib/CodeGen/DeadMachineInstructionElim.cpp
+++ b/llvm/lib/CodeGen/DeadMachineInstructionElim.cpp
@@ -10,9 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/Statistic.h"
-#include "llvm/CodeGen/LiveIntervals.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/CodeGen/Passes.h"
@@ -34,7 +32,6 @@ namespace {
     const TargetRegisterInfo *TRI;
     const MachineRegisterInfo *MRI;
     const TargetInstrInfo *TII;
-    LiveIntervals *LIS;
     BitVector LivePhysRegs;
 
   public:
@@ -44,7 +41,7 @@ namespace {
     }
 
     void getAnalysisUsage(AnalysisUsage &AU) const override {
-      AU.setPreservesAll();
+      AU.setPreservesCFG();
       MachineFunctionPass::getAnalysisUsage(AU);
     }
 
@@ -81,15 +78,9 @@ bool DeadMachineInstructionElim::isDead(const MachineInstr *MI) const {
       unsigned Reg = MO.getReg();
       if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
         // Don't delete live physreg defs, or any reserved register defs.
-        // Do not remove physreg defs if we have LIS as we may be unable
-        // to accurately recompute its liveness.
-        if (LivePhysRegs.test(Reg) || MRI->isReserved(Reg) || LIS)
+        if (LivePhysRegs.test(Reg) || MRI->isReserved(Reg))
           return false;
       } else {
-        // An instruction can also use its def in case if it is a tied operand.
-        // TODO: Technically we can also remove it if def dominates the use.
-        //       This can happen when two instructions define different subregs
-        //       of the same register.
         for (const MachineInstr &Use : MRI->use_nodbg_instructions(Reg)) {
           if (&Use != MI)
             // This def has a non-debug use. Don't delete the instruction!
@@ -111,8 +102,6 @@ bool DeadMachineInstructionElim::runOnMachineFunction(MachineFunction &MF) {
   MRI = &MF.getRegInfo();
   TRI = MF.getSubtarget().getRegisterInfo();
   TII = MF.getSubtarget().getInstrInfo();
-  LIS = getAnalysisIfAvailable<LiveIntervals>();
-  DenseSet<unsigned> RecalcRegs;
 
   // Loop over all instructions in all blocks, from bottom to top, so that it's
   // more likely that chains of dependent but ultimately dead instructions will
@@ -138,14 +127,6 @@ bool DeadMachineInstructionElim::runOnMachineFunction(MachineFunction &MF) {
       // If the instruction is dead, delete it!
       if (isDead(MI)) {
         LLVM_DEBUG(dbgs() << "DeadMachineInstructionElim: DELETING: " << *MI);
-        if (LIS) {
-          for (const MachineOperand &MO : MI->operands()) {
-            if (MO.isReg() && TRI->isVirtualRegister(MO.getReg()))
-              RecalcRegs.insert(MO.getReg());
-          }
-          LIS->RemoveMachineInstrFromMaps(*MI);
-        }
-
         // It is possible that some DBG_VALUE instructions refer to this
         // instruction.  They get marked as undef and will be deleted
         // in the live debug variable analysis.
@@ -189,12 +170,5 @@ bool DeadMachineInstructionElim::runOnMachineFunction(MachineFunction &MF) {
   }
 
   LivePhysRegs.clear();
-
-  for (auto Reg : RecalcRegs) {
-    LIS->removeInterval(Reg);
-    if (!MRI->reg_empty(Reg))
-      LIS->createAndComputeVirtRegInterval(Reg);
-  }
-
   return AnyChanges;
 }
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