[DebugInfo] Make postra sinking of DBG_VALUEs subregister-safe
Currently the machine instruction sinker identifies DBG_VALUE insts that also need to sink by comparing register numbers. Unfortunately this isn't safe, because (after register allocation) a DBG_VALUE may read a register that aliases what's being sunk. To fix this, identify the DBG_VALUEs that need to sink by recording & examining their register units. Register units gives us the following guarantee: "Two registers overlap if and only if they have a common register unit" [MCRegisterInfo.h] Thus we can always identify aliasing DBG_VALUEs if the set of register units read by the DBG_VALUE, and the register units of the instruction being sunk, intersect. (MachineSink already uses classes like "LiveRegUnits" for determining sinking validity anyway). The test added checks for super and subregister DBG_VALUE reads of a sunk copy being sunk as well. Differential Revision: https://reviews.llvm.org/D58191 llvm-svn: 369247
This commit is contained in:
Jeremy Morse
parent
2cafd872fb
commit
176bbd5cde
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@ -36,8 +36,9 @@
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#include "llvm/CodeGen/TargetRegisterInfo.h"
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#include "llvm/CodeGen/TargetSubtargetInfo.h"
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#include "llvm/IR/BasicBlock.h"
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#include "llvm/IR/LLVMContext.h"
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#include "llvm/IR/DebugInfoMetadata.h"
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#include "llvm/IR/LLVMContext.h"
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#include "llvm/MC/MCRegisterInfo.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/BranchProbability.h"
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#include "llvm/Support/CommandLine.h"
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@ -957,8 +958,9 @@ private:
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/// Track which register units have been modified and used.
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LiveRegUnits ModifiedRegUnits, UsedRegUnits;
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/// Track DBG_VALUEs of (unmodified) register units.
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DenseMap<unsigned, TinyPtrVector<MachineInstr*>> SeenDbgInstrs;
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/// Track DBG_VALUEs of (unmodified) register units. Each DBG_VALUE has an
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/// entry in this map for each unit it touches.
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DenseMap<unsigned, TinyPtrVector<MachineInstr *>> SeenDbgInstrs;
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/// Sink Copy instructions unused in the same block close to their uses in
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/// successors.
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@ -1093,6 +1095,14 @@ static bool hasRegisterDependency(MachineInstr *MI,
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return HasRegDependency;
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}
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static SmallSet<unsigned, 4> getRegUnits(unsigned Reg,
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const TargetRegisterInfo *TRI) {
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SmallSet<unsigned, 4> RegUnits;
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for (auto RI = MCRegUnitIterator(Reg, TRI); RI.isValid(); ++RI)
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RegUnits.insert(*RI);
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return RegUnits;
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}
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bool PostRAMachineSinking::tryToSinkCopy(MachineBasicBlock &CurBB,
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MachineFunction &MF,
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const TargetRegisterInfo *TRI,
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@ -1136,8 +1146,10 @@ bool PostRAMachineSinking::tryToSinkCopy(MachineBasicBlock &CurBB,
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ModifiedRegUnits, UsedRegUnits))
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continue;
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// Record debug use of this register.
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SeenDbgInstrs[MO.getReg()].push_back(MI);
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// Record debug use of each reg unit.
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SmallSet<unsigned, 4> Units = getRegUnits(MO.getReg(), TRI);
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for (unsigned Reg : Units)
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SeenDbgInstrs[Reg].push_back(MI);
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}
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continue;
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}
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@ -1176,15 +1188,22 @@ bool PostRAMachineSinking::tryToSinkCopy(MachineBasicBlock &CurBB,
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assert((SuccBB->pred_size() == 1 && *SuccBB->pred_begin() == &CurBB) &&
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"Unexpected predecessor");
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// Collect DBG_VALUEs that must sink with this copy.
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// Collect DBG_VALUEs that must sink with this copy. We've previously
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// recorded which reg units that DBG_VALUEs read, if this instruction
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// writes any of those units then the corresponding DBG_VALUEs must sink.
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SetVector<MachineInstr *> DbgValsToSinkSet;
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SmallVector<MachineInstr *, 4> DbgValsToSink;
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for (auto &MO : MI->operands()) {
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if (!MO.isReg() || !MO.isDef())
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continue;
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Register reg = MO.getReg();
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for (auto *MI : SeenDbgInstrs.lookup(reg))
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DbgValsToSink.push_back(MI);
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SmallSet<unsigned, 4> Units = getRegUnits(MO.getReg(), TRI);
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for (unsigned Reg : Units)
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for (auto *MI : SeenDbgInstrs.lookup(Reg))
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DbgValsToSinkSet.insert(MI);
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}
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DbgValsToSink.insert(DbgValsToSink.begin(), DbgValsToSinkSet.begin(),
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DbgValsToSinkSet.end());
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// Clear the kill flag if SrcReg is killed between MI and the end of the
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// block.
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@ -0,0 +1,104 @@
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# RUN: llc -mtriple=x86_64-unknown-unknown %s -run-pass=postra-machine-sink -o - | FileCheck %s
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# Test that when we run the postra machine sinker (which sinks COPYs), that
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# DBG_VALUEs of both sub and super-registers that depend on such COPYs are
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# sunk with them.
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--- |
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; Module stripped of everything, MIR below is what's interesting
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; ModuleID = '<stdin>'
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source_filename = "justacall.cpp"
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target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
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target triple = "x86_64-unknown-linux-gnu"
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; Function Attrs: noinline norecurse nounwind uwtable
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define dso_local i32 @main(i32 %argc, i8** nocapture readnone %argv) !dbg !14 {
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entry:
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br label %return
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return:
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ret i32 0
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}
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!llvm.dbg.cu = !{!2}
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!llvm.module.flags = !{!1, !1000}
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!0 = !{!"dummy metadata"}
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!1 = !{i32 2, !"Dwarf Version", i32 4}
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!1000 = !{i32 2, !"Debug Info Version", i32 3}
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!2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, producer: "clang", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, nameTableKind: None)
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!3 = !DIFile(filename: "justacall.cpp", directory: "/tmp")
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!4 = !{}
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!7 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
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!8 = !DIBasicType(name: "int", size: 8, encoding: DW_ATE_signed)
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!9 = !DIBasicType(name: "int", size: 16, encoding: DW_ATE_signed)
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!14 = distinct !DISubprogram(name: "main", scope: !3, file: !3, line: 7, type: !15, isLocal: false, isDefinition: true, scopeLine: 8, flags: DIFlagPrototyped, isOptimized: true, unit: !2, retainedNodes: !20)
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!15 = !DISubroutineType(types: !16)
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!16 = !{!7, !7}
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!20 = !{!21, !22, !23, !24}
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!21 = !DILocalVariable(name: "argc", arg: 1, scope: !14, file: !3, line: 7, type: !7)
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!22 = !DILocalVariable(name: "foo", scope: !14, file: !3, line: 7, type: !8)
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!23 = !DILocalVariable(name: "bar", scope: !14, file: !3, line: 7, type: !7)
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!24 = !DILocalVariable(name: "baz", scope: !14, file: !3, line: 7, type: !9)
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!100 = !DILocation(line: 1, scope: !14)
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...
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---
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name: main
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tracksRegLiveness: true
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registers:
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liveins:
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- { reg: '$edi', virtual-reg: '' }
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frameInfo:
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hasCalls: true
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fixedStack:
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stack:
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constants:
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body: |
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; CHECK: ![[ARGVAR:[0-9]+]] = !DILocalVariable(name: "argc",
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; CHECK: ![[FOOVAR:[0-9]+]] = !DILocalVariable(name: "foo",
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; CHECK: ![[BARVAR:[0-9]+]] = !DILocalVariable(name: "bar",
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; CHECK: ![[BAZVAR:[0-9]+]] = !DILocalVariable(name: "baz",
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; In the following code, the:
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; DBG_VALUE of $edi should not sink: it's an argument
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; DBG_VALUE of $ebx should sink: it's a standard copy
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; DBG_VALUE of $bx should sink: a write of its superregister sinks
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; DBG_VALUE of $ecx should sink: a write of one of its subregisters sinks
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; CHECK-LABEL: name: main
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; CHECK: bb.0.entry:
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; CHECK: successors: %bb.1(0x80000000)
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; CHECK: liveins: $edi
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; CHECK: DBG_VALUE $edi, $noreg, ![[BARVAR]]
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; CHECK-NEXT: renamable $cl = MOV8ri 1
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; CHECK-NEXT: JMP_1 %bb.1
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; CHECK: bb.1.return:
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; CHECK: liveins: $cl, $edi
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; CHECK: renamable $ebx = COPY $edi
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; CHECK-NEXT: DBG_VALUE $bx, $noreg, ![[BAZVAR]]
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; CHECK-NEXT: DBG_VALUE $ebx, $noreg, ![[ARGVAR]]
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; CHECK-NEXT: renamable $ch = COPY renamable $cl
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; CHECK-NEXT: DBG_VALUE $ecx, $noreg, ![[FOOVAR]]
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; CHECK-NEXT: $rdi = MOV32ri64 0
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; CHECK-NEXT: $eax = MOV32r0 implicit-def dead $eflags
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; CHECK-NEXT: RET 0, $eax
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bb.0.entry:
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successors: %bb.1(0x40000000)
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liveins: $edi
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DBG_VALUE $edi, $noreg, !23, !DIExpression(), debug-location !100
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renamable $ebx = COPY $edi
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DBG_VALUE $ebx, $noreg, !21, !DIExpression(), debug-location !100
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DBG_VALUE $bx, $noreg, !24, !DIExpression(), debug-location !100
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renamable $cl = MOV8ri 1, debug-location !100
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renamable $ch = COPY renamable $cl
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DBG_VALUE $ecx, $noreg, !22, !DIExpression(), debug-location !100
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JMP_1 %bb.1
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bb.1.return:
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liveins: $ebx, $ch
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$rdi = MOV32ri64 0
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$eax = MOV32r0 implicit-def dead $eflags
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RET 0, $eax
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...
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