Commit 2bf49662 authored by Vedant Kumar's avatar Vedant Kumar
Browse files

[LiveDebugValues] Do not insert DBG_VALUEs after a MBB terminator 

This fixes a miscompile that happened because a DBG_VALUE interfered
with the MachineOutliner's liveness analysis.

Inserting a DBG_VALUE after a terminator breaks predicates on MBB such
as isReturnBlock(). And the resulting DBG_VALUE cannot be "live".

I plan to introduce a MachineVerifier check for this situation in a
follow up.

rdar://59859175

Testing: check-llvm, LNT build with a stage2 compiler & entry values
enabled

Differential Revision: https://reviews.llvm.org/D75548
parent e70a9f38

llvm/lib/CodeGen/LiveDebugValues.cpp

+7 −0
Original line number Diff line number Diff line
@@ -959,6 +959,10 @@ void LiveDebugValues::emitEntryValues(MachineInstr &MI, 
                                      VarLocMap &VarLocIDs,

                                      TransferMap &Transfers,

                                      VarLocSet &KillSet) {

  // Do not insert entry value locations after a terminator.

  if (MI.isTerminator())

    return;



  for (uint64_t ID : KillSet) {

    LocIndex Idx = LocIndex::fromRawInteger(ID);

    const VarLoc &VL = VarLocIDs[Idx];
@@ -1003,6 +1007,7 @@ void LiveDebugValues::insertTransferDebugPair( 
    // Record the new location as an open range, and a postponed transfer

    // inserting a DBG_VALUE for this location.

    OpenRanges.insert(LocId, VL);

    assert(!MI.isTerminator() && "Cannot insert DBG_VALUE after terminator");

    TransferDebugPair MIP = {&MI, LocId};

    Transfers.push_back(MIP);

  };
@@ -1778,6 +1783,8 @@ bool LiveDebugValues::ExtendRanges(MachineFunction &MF) { 


  // Add any DBG_VALUE instructions created by location transfers.

  for (auto &TR : Transfers) {

    assert(!TR.TransferInst->isTerminator() &&

           "Cannot insert DBG_VALUE after terminator");

    MachineBasicBlock *MBB = TR.TransferInst->getParent();

    const VarLoc &VL = VarLocIDs[TR.LocationID];

    MachineInstr *MI = VL.BuildDbgValue(MF);

llvm/test/DebugInfo/MIR/X86/dbginfo-entryvals.mir

+2 −2
Original line number Diff line number Diff line 
# RUN: llc -debug-entry-values -run-pass=livedebugvalues -march=x86-64 -o - %s | FileCheck %s

# RUN: llc -debug-entry-values -run-pass=livedebugvalues -verify-machineinstrs -march=x86-64 -o - %s | FileCheck %s

#

#extern void fn2(int);

#
@@ -15,7 +15,7 @@ 
#  u --;

#}

# CHECK: DBG_VALUE $edi, $noreg, !14, !DIExpression(DW_OP_LLVM_entry_value, 1), debug-location {{.*}}

# CHECK: DBG_VALUE $esi, $noreg, !15, !DIExpression(DW_OP_LLVM_entry_value, 1), debug-location {{.*}}

# CHECK-NOT: DBG_VALUE $esi, $noreg, !15, !DIExpression(DW_OP_LLVM_entry_value, 1)



--- |

  ; ModuleID = 'test.c'