[PATCH] D18936: Fix regalloc-verifier error for r265547

[Wei Mi via llvm-commits]

wmi created this revision.
wmi added a reviewer: qcolombet.
wmi added subscribers: llvm-commits, davidxl.
wmi set the repository for this revision to rL LLVM.
Herald added a subscriber: MatzeB.

This is to fix the problem here:
http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20160404/345537.html

The error is caused by that I didn't create live interval for the dummy register used in rematerialization. regalloc-verifier requires any vreg has a live interval, and because it is a dummy register without live range segment, verifier requires it to be marked as Dead.

However, rematerialization may copy the dead flag to the instruction cloned, which is incorrect. So I need to set the Dead flag to false before doing rematerialization and reset it to true after that.
 

Repository:
  rL LLVM

http://reviews.llvm.org/D18936

Files:
  include/llvm/CodeGen/LiveRangeEdit.h
  lib/CodeGen/LiveRangeEdit.cpp
  test/CodeGen/X86/new-remat.ll

Index: test/CodeGen/X86/new-remat.ll
===================================================================
--- test/CodeGen/X86/new-remat.ll
+++ test/CodeGen/X86/new-remat.ll
@@ -1,4 +1,4 @@
-; RUN: llc < %s | FileCheck %s
+; RUN: llc -verify-regalloc < %s | FileCheck %s
 ; Check all spills are rematerialized.
 ; CHECK-NOT: Spill
 
Index: lib/CodeGen/LiveRangeEdit.cpp
===================================================================
--- lib/CodeGen/LiveRangeEdit.cpp
+++ lib/CodeGen/LiveRangeEdit.cpp
@@ -147,7 +147,23 @@
                                          const TargetRegisterInfo &tri,
                                          bool Late) {
   assert(RM.OrigMI && "Invalid remat");
+  // The dest operand of Inst in DeadRemats is set to Dead because it
+  // uses dummy register and MachineVerifier will check it.
+  // When inst in DeadRemats is used for remat, need to set the dest
+  // operand of the inst not to be Dead before reMaterialize and reset
+  // it to be Dead after. That is because otherwise the flag will be
+  // copied to the remat instruction newly created in reMaterialize
+  // whose dest operand we know is not Dead.
+  bool isDeadRemat = isDeadRematInstr(RM.OrigMI);
+  if (isDeadRemat)
+    RM.OrigMI->getOperand(0).setIsDead(false);
+
+  assert(!RM.OrigMI->getOperand(0).isDead() &&
+         "dest register of OrigMI cannot be Dead before remat");
   TII.reMaterialize(MBB, MI, DestReg, 0, RM.OrigMI, tri);
+
+  if (isDeadRemat)
+    RM.OrigMI->getOperand(0).setIsDead(true);
   Rematted.insert(RM.ParentVNI);
   return LIS.getSlotIndexes()
       ->insertMachineInstrInMaps(*--MI, Late)
@@ -325,12 +341,14 @@
     // The inst is saved in LiveRangeEdit::DeadRemats and will be deleted
     // after all the allocations of the func are done.
     if (isOrigDef) {
-      unsigned NewDest = createFrom(Dest);
+      LiveInterval &NewLI = createEmptyIntervalFrom(Dest);
+      VNInfo *VNI = NewLI.getNextValue(Idx, LIS.getVNInfoAllocator());
+      NewLI.addSegment(LiveInterval::Segment(Idx, Idx.getDeadSlot(), VNI));
       pop_back();
       markDeadRemat(MI);
       const TargetRegisterInfo &TRI = *MRI.getTargetRegisterInfo();
-      MI->substituteRegister(Dest, NewDest, 0, TRI);
-      MI->getOperand(0).setIsDead(false);
+      MI->substituteRegister(Dest, NewLI.reg, 0, TRI);
+      MI->getOperand(0).setIsDead(true);
     } else {
       if (TheDelegate)
         TheDelegate->LRE_WillEraseInstruction(MI);
Index: include/llvm/CodeGen/LiveRangeEdit.h
===================================================================
--- include/llvm/CodeGen/LiveRangeEdit.h
+++ include/llvm/CodeGen/LiveRangeEdit.h
@@ -231,6 +231,8 @@
       DeadRemats->insert(inst);
   }
 
+  bool isDeadRematInstr(MachineInstr *inst) { return DeadRemats->count(inst); }
+
   /// eraseVirtReg - Notify the delegate that Reg is no longer in use, and try
   /// to erase it from LIS.
   void eraseVirtReg(unsigned Reg);


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