[llvm] f5e1b71 - [DebugInfo] MachineSink: find more DBG_VALUEs to sink
Jeremy Morse via llvm-commits
llvm-commits at lists.llvm.org
Mon Oct 28 07:33:25 PDT 2019
Author: Jeremy Morse
Date: 2019-10-28T14:32:50Z
New Revision: f5e1b718a675a4449b71423f04d38e1e93045105
URL: https://github.com/llvm/llvm-project/commit/f5e1b718a675a4449b71423f04d38e1e93045105
DIFF: https://github.com/llvm/llvm-project/commit/f5e1b718a675a4449b71423f04d38e1e93045105.diff
LOG: [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
Added:
llvm/test/DebugInfo/MIR/X86/machinesink.mir
Modified:
llvm/lib/CodeGen/MachineSink.cpp
Removed:
################################################################################
diff --git a/llvm/lib/CodeGen/MachineSink.cpp b/llvm/lib/CodeGen/MachineSink.cpp
index 4c55158a0048..81fd30ca0529 100644
--- a/llvm/lib/CodeGen/MachineSink.cpp
+++ b/llvm/lib/CodeGen/MachineSink.cpp
@@ -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;
diff --git a/llvm/test/DebugInfo/MIR/X86/machinesink.mir b/llvm/test/DebugInfo/MIR/X86/machinesink.mir
new file mode 100644
index 000000000000..3df80ee15f51
--- /dev/null
+++ b/llvm/test/DebugInfo/MIR/X86/machinesink.mir
@@ -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
diff erent 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
+...
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