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[DebugInfo] MachineSink: find more DBG_VALUEs to sink 

In the Pre-RA machine sinker, previously we were relying on all DBG_VALUEs
being immediately after the instruction that defined their operands. This
isn't a valid assumption, as a variable location change doesn't
necessarily correspond to where the value is computed. In this patch, we
collect DBG_VALUEs that might need sinking as we walk through a block,
and sink all of them if their defining instruction is sunk.

This patch adds some copy propagation too, so that if we sink a copy inst,
the now non-dominated paths can use the copy source for the variable
location.

Differential Revision: https://reviews.llvm.org/D58386
This commit is contained in:
Jeremy Morse 2019-10-28 14:23:50 +00:00
parent 1ebd4a2e3a
commit f5e1b718a6
2 changed files with 191 additions and 15 deletions
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101
llvm/lib/CodeGen/MachineSink.cpp
View File

@ -105,6 +105,9 @@ namespace {
using AllSuccsCache =
std::map<MachineBasicBlock *, SmallVector<MachineBasicBlock *, 4>>;
// Remember debug uses of vregs seen, so we know what to sink out of blocks.
DenseMap<unsigned, TinyPtrVector<MachineInstr *>> SeenDbgUsers;
public:
static char ID; // Pass identification
@ -132,6 +135,7 @@ namespace {
private:
bool ProcessBlock(MachineBasicBlock &MBB);
void ProcessDbgInst(MachineInstr &MI);
bool isWorthBreakingCriticalEdge(MachineInstr &MI,
MachineBasicBlock *From,
MachineBasicBlock *To);
@ -153,8 +157,14 @@ namespace {
MachineBasicBlock *To,
bool BreakPHIEdge);
bool SinkInstruction(MachineInstr &MI, bool &SawStore,
AllSuccsCache &AllSuccessors);
/// If we sink a COPY inst, some debug users of it's destination may no
/// longer be dominated by the COPY, and will eventually be dropped.
/// This is easily rectified by forwarding the non-dominated debug uses
/// to the copy source.
void SalvageUnsunkDebugUsersOfCopy(MachineInstr &,
MachineBasicBlock *TargetBlock);
bool AllUsesDominatedByBlock(unsigned Reg, MachineBasicBlock *MBB,
MachineBasicBlock *DefMBB,
bool &BreakPHIEdge, bool &LocalUse) const;
@ -367,8 +377,11 @@ bool MachineSinking::ProcessBlock(MachineBasicBlock &MBB) {
if (!ProcessedBegin)
--I;
if (MI.isDebugInstr())
if (MI.isDebugInstr()) {
if (MI.isDebugValue())
ProcessDbgInst(MI);
continue;
}
bool Joined = PerformTrivialForwardCoalescing(MI, &MBB);
if (Joined) {
@ -384,9 +397,23 @@ bool MachineSinking::ProcessBlock(MachineBasicBlock &MBB) {
// If we just processed the first instruction in the block, we're done.
} while (!ProcessedBegin);
SeenDbgUsers.clear();
return MadeChange;
}
void MachineSinking::ProcessDbgInst(MachineInstr &MI) {
// When we see DBG_VALUEs for registers, record any vreg it reads, so that
// we know what to sink if the vreg def sinks.
assert(MI.isDebugValue() && "Expected DBG_VALUE for processing");
MachineOperand &MO = MI.getOperand(0);
if (!MO.isReg() || !MO.getReg().isVirtual())
return;
SeenDbgUsers[MO.getReg()].push_back(&MI);
}
bool MachineSinking::isWorthBreakingCriticalEdge(MachineInstr &MI,
MachineBasicBlock *From,
MachineBasicBlock *To) {
@ -731,22 +758,13 @@ static bool SinkingPreventsImplicitNullCheck(MachineInstr &MI,
MBP.LHS.getReg() == BaseOp->getReg();
}
/// Sink an instruction and its associated debug instructions. If the debug
/// instructions to be sunk are already known, they can be provided in DbgVals.
/// Sink an instruction and its associated debug instructions.
static void performSink(MachineInstr &MI, MachineBasicBlock &SuccToSinkTo,
MachineBasicBlock::iterator InsertPos,
SmallVectorImpl<MachineInstr *> *DbgVals = nullptr) {
SmallVectorImpl<MachineInstr *> &DbgValuesToSink) {
const MachineRegisterInfo &MRI = MI.getMF()->getRegInfo();
const TargetInstrInfo &TII = *MI.getMF()->getSubtarget().getInstrInfo();
// If debug values are provided use those, otherwise call collectDebugValues.
SmallVector<MachineInstr *, 2> DbgValuesToSink;
if (DbgVals)
DbgValuesToSink.insert(DbgValuesToSink.begin(),
DbgVals->begin(), DbgVals->end());
else
MI.collectDebugValues(DbgValuesToSink);
// If we cannot find a location to use (merge with), then we erase the debug
// location to prevent debug-info driven tools from potentially reporting
// wrong location information.
@ -929,7 +947,25 @@ bool MachineSinking::SinkInstruction(MachineInstr &MI, bool &SawStore,
while (InsertPos != SuccToSinkTo->end() && InsertPos->isPHI())
++InsertPos;
performSink(MI, *SuccToSinkTo, InsertPos);
// Collect debug users of any vreg that this inst defines.
SmallVector<MachineInstr *, 4> DbgUsersToSink;
for (auto &MO : MI.operands()) {
if (!MO.isReg() || !MO.isDef() || !MO.getReg().isVirtual())
continue;
if (!SeenDbgUsers.count(MO.getReg()))
continue;
auto &Users = SeenDbgUsers[MO.getReg()];
DbgUsersToSink.insert(DbgUsersToSink.end(), Users.begin(), Users.end());
}
// After sinking, some debug users may not be dominated any more. If possible,
// copy-propagate their operands. As it's expensive, don't do this if there's
// no debuginfo in the program.
if (MI.getMF()->getFunction().getSubprogram() && MI.isCopy())
SalvageUnsunkDebugUsersOfCopy(MI, SuccToSinkTo);
performSink(MI, *SuccToSinkTo, InsertPos, DbgUsersToSink);
// Conservatively, clear any kill flags, since it's possible that they are no
// longer correct.
@ -944,6 +980,41 @@ bool MachineSinking::SinkInstruction(MachineInstr &MI, bool &SawStore,
return true;
}
void MachineSinking::SalvageUnsunkDebugUsersOfCopy(
MachineInstr &MI, MachineBasicBlock *TargetBlock) {
assert(MI.isCopy());
assert(MI.getOperand(1).isReg());
// Enumerate all users of vreg operands that are def'd. Skip those that will
// be sunk. For the rest, if they are not dominated by the block we will sink
// MI into, propagate the copy source to them.
SmallVector<MachineInstr *, 4> DbgDefUsers;
const MachineRegisterInfo &MRI = MI.getMF()->getRegInfo();
for (auto &MO : MI.operands()) {
if (!MO.isReg() || !MO.isDef() || !MO.getReg().isVirtual())
continue;
for (auto &User : MRI.use_instructions(MO.getReg())) {
if (!User.isDebugValue() || DT->dominates(TargetBlock, User.getParent()))
continue;
// If is in same block, will either sink or be use-before-def.
if (User.getParent() == MI.getParent())
continue;
assert(User.getOperand(0).isReg() &&
"DBG_VALUE user of vreg, but non reg operand?");
DbgDefUsers.push_back(&User);
}
}
// Point the users of this copy that are no longer dominated, at the source
// of the copy.
for (auto *User : DbgDefUsers) {
User->getOperand(0).setReg(MI.getOperand(1).getReg());
User->getOperand(0).setSubReg(MI.getOperand(1).getSubReg());
}
}
//===----------------------------------------------------------------------===//
// This pass is not intended to be a replacement or a complete alternative
// for the pre-ra machine sink pass. It is only designed to sink COPY
@ -1253,7 +1324,7 @@ bool PostRAMachineSinking::tryToSinkCopy(MachineBasicBlock &CurBB,
// block.
clearKillFlags(MI, CurBB, UsedOpsInCopy, UsedRegUnits, TRI);
MachineBasicBlock::iterator InsertPos = SuccBB->getFirstNonPHI();
performSink(*MI, *SuccBB, InsertPos, &DbgValsToSink);
performSink(*MI, *SuccBB, InsertPos, DbgValsToSink);
updateLiveIn(MI, SuccBB, UsedOpsInCopy, DefedRegsInCopy);
Changed = true;

105
llvm/test/DebugInfo/MIR/X86/machinesink.mir Normal file
View File

@ -0,0 +1,105 @@
# RUN: llc -mtriple=x86_64-unknown-unknown -run-pass=machine-sink -o - %s | FileCheck %s
# Check various things when we sink machine instructions:
# a) DBG_VALUEs should sink with defs
# b) Undefs should be left behind
# c) DBG_VALUEs not immediately following the defining inst should sink too
# d) If we generate debug-use-before-defs through sinking, and can copy
# propagate to a different value, we should do that.
--- |
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
@x = common local_unnamed_addr global i32 0, align 4, !dbg !0
; Function Attrs: noreturn nounwind uwtable
define void @Process(i32* nocapture readonly %p) local_unnamed_addr !dbg !9 {
; Stripped
entry:
br label %nou
nou:
br label %exit
exit:
ret void
}
; Function Attrs: nounwind readnone
declare void @llvm.dbg.value(metadata, i64, metadata, metadata)
!llvm.dbg.cu = !{!1}
!llvm.module.flags = !{!6, !7}
!llvm.ident = !{!8}
!0 = !DIGlobalVariableExpression(var: !DIGlobalVariable(name: "x", scope: !1, file: !2, line: 1, type: !5, isLocal: false, isDefinition: true), expr: !DIExpression())
!1 = distinct !DICompileUnit(language: DW_LANG_C99, file: !2, producer: "clang", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !3, globals: !4)
!2 = !DIFile(filename: "t.c", directory: "")
!3 = !{}
!4 = !{!0}
!5 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
!6 = !{i32 2, !"Dwarf Version", i32 4}
!7 = !{i32 2, !"Debug Info Version", i32 3}
!8 = !{!"clang version 4.0.0 "}
!9 = distinct !DISubprogram(name: "Process", scope: !2, file: !2, line: 2, type: !10, isLocal: false, isDefinition: true, scopeLine: 3, flags: DIFlagPrototyped, isOptimized: true, unit: !1, retainedNodes: !15)
!10 = !DISubroutineType(types: !11)
!11 = !{null, !12}
!12 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !13, size: 64)
!13 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !14)
!14 = !DIBasicType(name: "unsigned int", size: 32, encoding: DW_ATE_unsigned)
!15 = !{!16}
!16 = !DILocalVariable(name: "p", arg: 1, scope: !9, file: !2, line: 2, type: !12)
!17 = !DIExpression()
!18 = !DILocation(line: 2, column: 34, scope: !9)
!28 = !DILexicalBlockFile(scope: !9, file: !2, discriminator: 1)
; CHECK: [[VARNUM:![0-9]+]] = !DILocalVariable(name: "p",
...
---
name: Process
tracksRegLiveness: true
liveins:
- { reg: '$rdi', virtual-reg: '%2' }
- { reg: '$rsi', virtual-reg: '%2' }
body: |
bb.0.entry:
successors: %bb.1.nou(0x80000000), %bb.2.exit
liveins: $rdi, $esi
; This block should have the vreg copy sunk from it, the DBG_VALUE with it,
; and a copy-prop'd DBG_VALUE left over.
; CHECK-LABEL: bb.0.entry:
; CHECK: [[ARG0VREG:%[0-9]+]]:gr64 = COPY $rdi
; CHECK-NEXT: CMP32ri $esi, 0
; CHECK-NEXT: DBG_VALUE [[ARG0VREG]], $noreg, [[VARNUM]]
; CHECK-NEXT: JCC_1 %bb.1, 4
; CHECK-NEXT: JMP_1
%2:gr64 = COPY $rdi
%5:gr64 = COPY %2
CMP32ri $esi, 0, implicit-def $eflags
DBG_VALUE %5, $noreg, !16, !17, debug-location !18
JCC_1 %bb.1.nou, 4, implicit $eflags
JMP_1 %bb.2.exit
bb.1.nou:
successors: %bb.2.exit(0x80000000)
; This block should receive the sunk copy and DBG_VALUE
; CHECK-LABEL: bb.1.nou:
; CHECK: [[SUNKVREG:%[0-9]+]]:gr64 = COPY [[ARG0VREG]]
; CHECK-NEXT: DBG_VALUE [[SUNKVREG]], $noreg, [[VARNUM]]
; CHECK-NEXT: ADD64ri8
; CHECK-NEXT: JMP_1
%1:gr64 = ADD64ri8 %5, 4, implicit-def dead $eflags
JMP_1 %bb.2.exit
bb.2.exit:
; The DBG_VALUE below should have its operand copy-propagated after
; the copy to %5 is sunk.
; CHECK-LABEL: bb.2.exit:
; CHECK: DBG_VALUE [[ARG0VREG]], $noreg, [[VARNUM]]
; CHECK-NEXT: $rax = MOV64rr [[ARG0VREG]]
; CHECK-NEXT: RET 0
DBG_VALUE %5, _, !16, !17, debug-location !18
$rax = MOV64rr %2
RET 0
...