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r369026 | jmorse | 2019-08-15 19:49:46 +0200 (Thu, 15 Aug 2019) | 17 lines

[DebugInfo] Avoid crash from dropped fragments in LiveDebugValues

This patch avoids a crash caused by DW_OP_LLVM_fragments being dropped
from DIExpressions by LiveDebugValues spill-restore code. The appearance
of a previously unseen fragment configuration confuses LDV, as documented
in PR42773, and reproduced by the test function this patch adds (Crashes
on a x86_64 debug build).

To avoid this, on spill restore, we now use fragment information from the
spilt-location-expression.

In addition, when spilling, we now don't spill any DBG_VALUE with a complex
expression, as it can't be safely restored and will definitely lead to an
incorrect variable location. The discussion of this is in D65368.

Differential Revision: https://reviews.llvm.org/D66284

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llvm-svn: 369354
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zmodem committed Aug 20, 2019
1 parent 0c67478 commit 10f293f
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Showing 2 changed files with 128 additions and 4 deletions.
17 changes: 15 additions & 2 deletions llvm/lib/CodeGen/LiveDebugValues.cpp
Expand Up @@ -691,9 +691,17 @@ void LiveDebugValues::insertTransferDebugPair(
"No register supplied when handling a restore of a debug value");
MachineFunction *MF = MI.getMF();
DIBuilder DIB(*const_cast<Function &>(MF->getFunction()).getParent());

const DIExpression *NewExpr;
if (auto Fragment = DebugInstr->getDebugExpression()->getFragmentInfo())
NewExpr = *DIExpression::createFragmentExpression(DIB.createExpression(),
Fragment->OffsetInBits, Fragment->SizeInBits);
else
NewExpr = DIB.createExpression();

NewDebugInstr =
BuildMI(*MF, DebugInstr->getDebugLoc(), DebugInstr->getDesc(), false,
NewReg, DebugInstr->getDebugVariable(), DIB.createExpression());
NewReg, DebugInstr->getDebugVariable(), NewExpr);
VarLoc VL(*NewDebugInstr, LS);
ProcessVarLoc(VL, NewDebugInstr);
LLVM_DEBUG(dbgs() << "Creating DBG_VALUE inst for register restore: ";
Expand Down Expand Up @@ -848,9 +856,14 @@ void LiveDebugValues::transferSpillOrRestoreInst(MachineInstr &MI,
<< "\n");
}
// Check if the register or spill location is the location of a debug value.
// FIXME: Don't create a spill transfer if there is a complex expression,
// because we currently cannot recover the original expression on restore.
for (unsigned ID : OpenRanges.getVarLocs()) {
const MachineInstr *DebugInstr = &VarLocIDs[ID].MI;

if (TKind == TransferKind::TransferSpill &&
VarLocIDs[ID].isDescribedByReg() == Reg) {
VarLocIDs[ID].isDescribedByReg() == Reg &&
!DebugInstr->getDebugExpression()->isComplex()) {
LLVM_DEBUG(dbgs() << "Spilling Register " << printReg(Reg, TRI) << '('
<< VarLocIDs[ID].Var.getVar()->getName() << ")\n");
} else if (TKind == TransferKind::TransferRestore &&
Expand Down
115 changes: 113 additions & 2 deletions llvm/test/DebugInfo/MIR/X86/live-debug-values-restore.mir
Expand Up @@ -14,13 +14,17 @@
# return *(p + 1);
# }

# Pick out DILocalVariable numbers for "p" and "q"
# CHECK: ![[PVAR:[0-9]+]] = !DILocalVariable(name: "p",
# CHECK: ![[QVAR:[0-9]+]] = !DILocalVariable(name: "q",

# Ascertain that the spill has been recognized and manifested in a DBG_VALUE.
# CHECK: MOV64mr $rsp,{{.*-8.*}}killed{{.*}}$rdi :: (store 8 into %stack.0)
# CHECK-NEXT: DBG_VALUE $rsp,{{.*}}![[MDIX:[0-9]+]],{{.*}}!DIExpression(DW_OP_constu, 8, DW_OP_minus)
# CHECK-NEXT: DBG_VALUE $rsp,{{.*}}![[PVAR]],{{.*}}!DIExpression(DW_OP_constu, 8, DW_OP_minus)

# Check for the restore.
# CHECK: $rdi = MOV64rm $rsp,{{.*-8.*}}:: (load 8 from %stack.0)
# CHECK-NEXT: DBG_VALUE $rdi,{{.*}}![[MDIX]], !DIExpression()
# CHECK-NEXT: DBG_VALUE $rdi,{{.*}}![[PVAR]], !DIExpression()

--- |
define dso_local i32 @f(i32* readonly %p) local_unnamed_addr !dbg !7 {
Expand All @@ -39,6 +43,22 @@
ret i32 %0, !dbg !28
}

define dso_local i32 @g(i32* readonly %p) local_unnamed_addr !dbg !107 {
entry:
call void @llvm.dbg.value(metadata i32* %p, metadata !113, metadata !DIExpression()), !dbg !114
%tobool = icmp eq i32* %p, null, !dbg !115
br i1 %tobool, label %if.end, label %if.then, !dbg !117

if.then: ; preds = %entry
tail call void asm sideeffect "", "~{rax},~{rbx},~{rcx},~{rdx},~{rsi},~{rdi},~{rbp},~{r8},~{r9},~{r10},~{r11},~{r12},~{r13},~{r14},~{r15},~{dirflag},~{fpsr},~{flags}"(), !dbg !118, !srcloc !120
br label %if.end, !dbg !121

if.end: ; preds = %entry, %if.then
%add.ptr = getelementptr inbounds i32, i32* %p, i64 1, !dbg !122
%0 = load i32, i32* %add.ptr, align 4, !dbg !123, !tbaa !24
ret i32 %0, !dbg !128
}

declare void @llvm.dbg.value(metadata, metadata, metadata)

!llvm.dbg.cu = !{!0}
Expand Down Expand Up @@ -74,6 +94,22 @@
!26 = !{!"omnipotent char", !27, i64 0}
!27 = !{!"Simple C/C++ TBAA"}
!28 = !DILocation(line: 9, column: 3, scope: !7)
!101 = !DIBasicType(name: "looong int", size: 64, encoding: DW_ATE_signed)
!107 = distinct !DISubprogram(name: "g", scope: !1, file: !1, line: 105, type: !8, scopeLine: 105, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !112)
!112 = !{!113}
!113 = !DILocalVariable(name: "q", arg: 1, scope: !107, file: !1, line: 105, type: !101)
!114 = !DILocation(line: 105, column: 12, scope: !107)
!115 = !DILocation(line: 106, column: 7, scope: !116)
!116 = distinct !DILexicalBlock(scope: !107, file: !1, line: 106, column: 7)
!117 = !DILocation(line: 106, column: 7, scope: !107)
!118 = !DILocation(line: 107, column: 5, scope: !119)
!119 = distinct !DILexicalBlock(scope: !116, file: !1, line: 106, column: 10)
!120 = !{i32 -2147471544}
!121 = !DILocation(line: 108, column: 3, scope: !119)
!122 = !DILocation(line: 109, column: 14, scope: !107)
!123 = !DILocation(line: 109, column: 10, scope: !107)
!128 = !DILocation(line: 109, column: 3, scope: !107)


...
---
Expand Down Expand Up @@ -187,3 +223,78 @@ body: |
RETQ $eax, debug-location !28
...
---
# This second function has been appended as a regression test against a
# crash, caused by expressions being created from spill restores that did
# not preserve fragment information. Test that no empty expressions are
# created at all, and the last block describes both variable fragments.

# CHECK-LABEL: name: g
# CHECK-NOT: !DIExpression()
# CHECK-LABEL: bb.2.if.end:
# CHECK: DBG_VALUE $rdi, $noreg, ![[QVAR]], !DIExpression(DW_OP_LLVM_fragment, 0, 32)
# CHECK-NEXT: DBG_VALUE $rbx, $noreg, ![[QVAR]], !DIExpression(DW_OP_LLVM_fragment, 32, 32)

name: g
alignment: 4
tracksRegLiveness: true
liveins:
- { reg: '$rdi', virtual-reg: '' }
frameInfo:
stackSize: 48
offsetAdjustment: -48
maxAlignment: 8
cvBytesOfCalleeSavedRegisters: 48
localFrameSize: 0
fixedStack:
- { id: 0, type: spill-slot, offset: -56, size: 8, alignment: 8, stack-id: default,
callee-saved-register: '$rbx', callee-saved-restored: true, debug-info-variable: '',
debug-info-expression: '', debug-info-location: '' }
- { id: 1, type: spill-slot, offset: -48, size: 8, alignment: 16, stack-id: default,
callee-saved-register: '$r12', callee-saved-restored: true, debug-info-variable: '',
debug-info-expression: '', debug-info-location: '' }
- { id: 2, type: spill-slot, offset: -40, size: 8, alignment: 8, stack-id: default,
callee-saved-register: '$r13', callee-saved-restored: true, debug-info-variable: '',
debug-info-expression: '', debug-info-location: '' }
- { id: 3, type: spill-slot, offset: -32, size: 8, alignment: 16, stack-id: default,
callee-saved-register: '$r14', callee-saved-restored: true, debug-info-variable: '',
debug-info-expression: '', debug-info-location: '' }
- { id: 4, type: spill-slot, offset: -24, size: 8, alignment: 8, stack-id: default,
callee-saved-register: '$r15', callee-saved-restored: true, debug-info-variable: '',
debug-info-expression: '', debug-info-location: '' }
- { id: 5, type: spill-slot, offset: -16, size: 8, alignment: 16, stack-id: default,
callee-saved-register: '$rbp', callee-saved-restored: true, debug-info-variable: '',
debug-info-expression: '', debug-info-location: '' }
stack:
- { id: 0, name: '', type: spill-slot, offset: -64, size: 8, alignment: 8,
stack-id: default, callee-saved-register: '', callee-saved-restored: true,
debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
constants: []
body: |
bb.0.entry:
successors: %bb.1(0x50000000)
liveins: $rdi, $rbx, $r12, $r13, $r14, $r15, $rbp
DBG_VALUE $rdi, $noreg, !113, !DIExpression(DW_OP_LLVM_fragment, 0, 32), debug-location !114
TEST64rr renamable $rdi, renamable $rdi, implicit-def $eflags, debug-location !115
JMP_1 %bb.1, implicit $eflags, debug-location !117
bb.1.if.then:
successors: %bb.2(0x80000000)
liveins: $rdi, $rbp, $r15, $r14, $r13, $r12, $rbx
MOV64mr $rsp, 1, $noreg, -8, $noreg, killed renamable $rdi :: (store 8 into %stack.0)
renamable $rdi = MOV64rm $rsp, 1, $noreg, -8, $noreg :: (load 8 from %stack.0)
bb.2.if.end:
liveins: $rdi, $rbx, $r12, $r13, $r14, $r15, $rbp
DBG_VALUE $rbx, $noreg, !113, !DIExpression(DW_OP_LLVM_fragment, 32, 32), debug-location !114
MOV64mr $rsp, 1, $noreg, -8, $noreg, killed renamable $rbx :: (store 8 into %stack.0)
renamable $rsi = MOV64rm $rsp, 1, $noreg, -8, $noreg :: (load 8 from %stack.0)
renamable $eax = MOV32rm killed renamable $rsi, 1, $noreg, 4, $noreg, debug-location !123 :: (load 4 from %ir.add.ptr, !tbaa !24)
$rdi = MOV64ri 0
RETQ $eax, debug-location !128
...

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