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[LiveDebugValues] Do not insert DBG_VALUEs after a MBB terminator

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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
This commit is contained in:
Vedant Kumar 2020-03-03 11:08:48 -08:00
parent ed198c45c9
commit 4933893b80
2 changed files with 9 additions and 2 deletions
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7
lib/CodeGen/LiveDebugValues.cpp
View File

@ -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);

4
test/DebugInfo/MIR/X86/dbginfo-entryvals.mir
View File

@ -1,4 +1,4 @@
# 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'