[llvm] r368835 - [DebugInfo] MCP: collect and update DBG_VALUEs encountered in local block
Jeremy Morse via llvm-commits
llvm-commits at lists.llvm.org
Wed Aug 14 05:20:03 PDT 2019
Author: jmorse
Date: Wed Aug 14 05:20:02 2019
New Revision: 368835
URL: http://llvm.org/viewvc/llvm-project?rev=368835&view=rev
Log:
[DebugInfo] MCP: collect and update DBG_VALUEs encountered in local block
MCP currently uses changeDebugValuesDefReg / collectDebugValues to find
debug users of a register, however those functions assume that all
DBG_VALUEs immediately follow the specified instruction, which isn't
necessarily true. This is going to become very often untrue when we turn
off CodeGenPrepare::placeDbgValues.
Instead of calling changeDebugValuesDefReg on an instruction to change its
debug users, in this patch we instead collect DBG_VALUEs of copies as we
iterate over insns, and update the debug users of copies that are made
dead. This isn't a non-functional change, because MCP will now update
DBG_VALUEs that aren't immediately after a copy, but refer to the same
register. I've hijacked the regression test for PR38773 to test for this
new behaviour, an entirely new test seemed overkill.
Differential Revision: https://reviews.llvm.org/D56265
Modified:
llvm/trunk/include/llvm/CodeGen/MachineRegisterInfo.h
llvm/trunk/lib/CodeGen/MachineCopyPropagation.cpp
llvm/trunk/test/CodeGen/MIR/X86/pr38773.mir
Modified: llvm/trunk/include/llvm/CodeGen/MachineRegisterInfo.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/CodeGen/MachineRegisterInfo.h?rev=368835&r1=368834&r2=368835&view=diff
==============================================================================
--- llvm/trunk/include/llvm/CodeGen/MachineRegisterInfo.h (original)
+++ llvm/trunk/include/llvm/CodeGen/MachineRegisterInfo.h Wed Aug 14 05:20:02 2019
@@ -818,6 +818,17 @@ public:
/// deleted during LiveDebugVariables analysis.
void markUsesInDebugValueAsUndef(unsigned Reg) const;
+ /// updateDbgUsersToReg - Update a collection of DBG_VALUE instructions
+ /// to refer to the designated register.
+ void updateDbgUsersToReg(unsigned Reg,
+ ArrayRef<MachineInstr*> Users) const {
+ for (MachineInstr *MI : Users) {
+ assert(MI->isDebugInstr());
+ assert(MI->getOperand(0).isReg());
+ MI->getOperand(0).setReg(Reg);
+ }
+ }
+
/// Return true if the specified register is modified in this function.
/// This checks that no defining machine operands exist for the register or
/// any of its aliases. Definitions found on functions marked noreturn are
Modified: llvm/trunk/lib/CodeGen/MachineCopyPropagation.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/MachineCopyPropagation.cpp?rev=368835&r1=368834&r2=368835&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/MachineCopyPropagation.cpp (original)
+++ llvm/trunk/lib/CodeGen/MachineCopyPropagation.cpp Wed Aug 14 05:20:02 2019
@@ -205,8 +205,11 @@ public:
}
private:
+ typedef enum { DebugUse = false, RegularUse = true } DebugType;
+
void ClobberRegister(unsigned Reg);
- void ReadRegister(unsigned Reg);
+ void ReadRegister(unsigned Reg, MachineInstr &Reader,
+ DebugType DT);
void CopyPropagateBlock(MachineBasicBlock &MBB);
bool eraseIfRedundant(MachineInstr &Copy, unsigned Src, unsigned Def);
void forwardUses(MachineInstr &MI);
@@ -217,6 +220,9 @@ private:
/// Candidates for deletion.
SmallSetVector<MachineInstr *, 8> MaybeDeadCopies;
+ /// Multimap tracking debug users in current BB
+ DenseMap<MachineInstr*, SmallVector<MachineInstr*, 2>> CopyDbgUsers;
+
CopyTracker Tracker;
bool Changed;
@@ -231,13 +237,19 @@ char &llvm::MachineCopyPropagationID = M
INITIALIZE_PASS(MachineCopyPropagation, DEBUG_TYPE,
"Machine Copy Propagation Pass", false, false)
-void MachineCopyPropagation::ReadRegister(unsigned Reg) {
+void MachineCopyPropagation::ReadRegister(unsigned Reg, MachineInstr &Reader,
+ DebugType DT) {
// If 'Reg' is defined by a copy, the copy is no longer a candidate
- // for elimination.
+ // for elimination. If a copy is "read" by a debug user, record the user
+ // for propagation.
for (MCRegUnitIterator RUI(Reg, TRI); RUI.isValid(); ++RUI) {
if (MachineInstr *Copy = Tracker.findCopyForUnit(*RUI, *TRI)) {
- LLVM_DEBUG(dbgs() << "MCP: Copy is used - not dead: "; Copy->dump());
- MaybeDeadCopies.remove(Copy);
+ if (DT == RegularUse) {
+ LLVM_DEBUG(dbgs() << "MCP: Copy is used - not dead: "; Copy->dump());
+ MaybeDeadCopies.remove(Copy);
+ } else {
+ CopyDbgUsers[Copy].push_back(&Reader);
+ }
}
}
}
@@ -488,14 +500,14 @@ void MachineCopyPropagation::CopyPropaga
// If Src is defined by a previous copy, the previous copy cannot be
// eliminated.
- ReadRegister(Src);
+ ReadRegister(Src, *MI, RegularUse);
for (const MachineOperand &MO : MI->implicit_operands()) {
if (!MO.isReg() || !MO.readsReg())
continue;
unsigned Reg = MO.getReg();
if (!Reg)
continue;
- ReadRegister(Reg);
+ ReadRegister(Reg, *MI, RegularUse);
}
LLVM_DEBUG(dbgs() << "MCP: Copy is a deletion candidate: "; MI->dump());
@@ -534,7 +546,7 @@ void MachineCopyPropagation::CopyPropaga
// instruction, so we need to make sure we don't remove it as dead
// later.
if (MO.isTied())
- ReadRegister(Reg);
+ ReadRegister(Reg, *MI, RegularUse);
Tracker.clobberRegister(Reg, *TRI);
}
@@ -558,8 +570,8 @@ void MachineCopyPropagation::CopyPropaga
if (MO.isDef() && !MO.isEarlyClobber()) {
Defs.push_back(Reg);
continue;
- } else if (!MO.isDebug() && MO.readsReg())
- ReadRegister(Reg);
+ } else if (MO.readsReg())
+ ReadRegister(Reg, *MI, MO.isDebug() ? DebugUse : RegularUse);
}
// The instruction has a register mask operand which means that it clobbers
@@ -609,9 +621,10 @@ void MachineCopyPropagation::CopyPropaga
MaybeDead->dump());
assert(!MRI->isReserved(MaybeDead->getOperand(0).getReg()));
- // Update matching debug values.
+ // Update matching debug values, if any.
assert(MaybeDead->isCopy());
- MaybeDead->changeDebugValuesDefReg(MaybeDead->getOperand(1).getReg());
+ unsigned SrcReg = MaybeDead->getOperand(1).getReg();
+ MRI->updateDbgUsersToReg(SrcReg, CopyDbgUsers[MaybeDead]);
MaybeDead->eraseFromParent();
Changed = true;
@@ -620,6 +633,7 @@ void MachineCopyPropagation::CopyPropaga
}
MaybeDeadCopies.clear();
+ CopyDbgUsers.clear();
Tracker.clear();
}
Modified: llvm/trunk/test/CodeGen/MIR/X86/pr38773.mir
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/MIR/X86/pr38773.mir?rev=368835&r1=368834&r2=368835&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/MIR/X86/pr38773.mir (original)
+++ llvm/trunk/test/CodeGen/MIR/X86/pr38773.mir Wed Aug 14 05:20:02 2019
@@ -99,6 +99,13 @@ body: |
; CHECK: IDIV32r killed renamable $ecx
; CHECK-NEXT: DBG_VALUE $eax, $noreg, !12, !DIExpression(), debug-location !13
DBG_VALUE $ecx, $noreg, !12, !DIExpression(), debug-location !13
+ ; The following mov and DBG_VALUE have been inserted after the PR was
+ ; resolved to check that MCP will update debug users that are not
+ ; immediately after the dead copy.
+ ; CHECK-NEXT: $edx = MOV32r0
+ $edx = MOV32r0 implicit-def dead $eflags
+ ; CHECK-NEXT: DBG_VALUE $eax, $noreg, !12, !DIExpression(), debug-location !13
+ DBG_VALUE $ecx, $noreg, !12, !DIExpression(), debug-location !13
$eax = COPY killed renamable $ecx
RET 0, $eax
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