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[DebugInfo][InstrRef] Fix a tombstone-in-DenseMap crash from D117877
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This is a follow-up to D117877: variable assignments of DBG_VALUE $noreg,
or DBG_INSTR_REFs where no value can be found, are represented by a
DbgValue object with Kind "Undef", explicitly meaning "there is no value".
In D117877 I added a special-case to some assignment accounting faster,
without considering this scenario. It causes variables to be given the
value ValueIDNum::EmptyValue, which then ends up being a DenseMap key. The
DenseMap asserts, because EmptyValue is the tombstone key.

Fix this by handling the assign-undef scenario in the special case, to
match what happens in the general case: the variable has no value if it's
only ever assigned $noreg / undef.

Differential Revision: https://reviews.llvm.org/D118715
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jmorse committed Feb 2, 2022
1 parent c5fff90 commit 43de305
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Showing 2 changed files with 68 additions and 2 deletions.
5 changes: 5 additions & 0 deletions llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp
Original file line number Diff line number Diff line change
Expand Up @@ -2796,6 +2796,11 @@ void InstrRefBasedLDV::placePHIsForSingleVarDefinition(
auto ValueIt = VLocs.Vars.find(Var);
const DbgValue &Value = ValueIt->second;

// If it's an explicit assignment of "undef", that means there is no location
// anyway, anywhere.
if (Value.Kind == DbgValue::Undef)
return;

// Assign the variable value to entry to each dominated block that's in scope.
// Skip the definition block -- it's assigned the variable value in the middle
// of the block somewhere.
Expand Down
65 changes: 63 additions & 2 deletions llvm/test/DebugInfo/MIR/InstrRef/single-assign-propagation.mir
Original file line number Diff line number Diff line change
@@ -1,9 +1,11 @@
# RUN: llc %s -march=x86-64 -run-pass=livedebugvalues -o - \
# RUN: -experimental-debug-variable-locations=true \
# RUN: | FileCheck %s -implicit-check-not=DBG_VALUE
# RUN: | FileCheck %s -implicit-check-not=DBG_VALUE \
# RUN: --check-prefixes=CHECK,COMMON
# RUN: llc %s -march=x86-64 -run-pass=livedebugvalues -o - \
# RUN: -experimental-debug-variable-locations=false \
# RUN: | FileCheck %s --check-prefixes=VARLOC -implicit-check-not=DBG_VALUE
# RUN: | FileCheck %s -implicit-check-not=DBG_VALUE \
# RUN: --check-prefixes=VARLOC,COMMON
#
# This test is designed to stimulate a simplification of variable-value
# propagation in InstrRefBasedLDV. When we only have a single assignment of
Expand Down Expand Up @@ -63,12 +65,23 @@
# VARLOC-LABEL: bb.3:
# VARLOC: DBG_VALUE
#
## Common tail for 'test2' -- this is checking that the assignment of undef or
## $noreg in single-assignment mode doesn't lead to trouble further down the
## line, specifically assertion failures.
#
# COMMON-LABEL: name: test2
# COMMON: DBG_VALUE $noreg
--- |
define i32 @_Z8bb_to_bb() local_unnamed_addr !dbg !12 {
entry:
ret i32 0, !dbg !17
}

define i32 @test2() local_unnamed_addr !dbg !112 {
entry:
ret i32 0, !dbg !117
}

!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!7, !8, !9, !10}
!llvm.ident = !{!11}
Expand All @@ -94,6 +107,13 @@
!18 = distinct !DILexicalBlock(scope: !12, file: !1, line: 1, column: 1)
!19 = distinct !DILexicalBlock(scope: !12, file: !1, line: 1, column: 1)
!20 = !DILocation(line: 10, scope: !19)
!112 = distinct !DISubprogram(name: "test2", linkageName: "102", scope: !1, file: !1, line: 6, type: !13, scopeLine: 6, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !115)
!115 = !{!116}
!116 = !DILocalVariable(name: "myVar", scope: !118, file: !1, line: 7, type: !6)
!117 = !DILocation(line: 10, scope: !118)
!118 = distinct !DILexicalBlock(scope: !112, file: !1, line: 1, column: 1)
!119 = distinct !DILexicalBlock(scope: !112, file: !1, line: 1, column: 1)
!120 = !DILocation(line: 10, scope: !119)

...
---
Expand Down Expand Up @@ -136,3 +156,44 @@ body: |
bb.6:
RET 0, debug-location !17
...
---
name: test2
debugValueSubstitutions:
- { srcinst: 4, srcop: 0, dstinst: 3, dstop: 0, subreg: 0 }
body: |
bb.0.entry:
successors: %bb.1, %bb.5, %bb.6
$rax = MOV64ri 1, debug-instr-number 1, debug-location !117
JCC_1 %bb.5, 1, implicit $eflags
JCC_1 %bb.6, 2, implicit $eflags
JMP_1 %bb.1
bb.1:
successors: %bb.2, %bb.3
DBG_VALUE $noreg, $noreg, !116, !DIExpression(), debug-location !117
JCC_1 %bb.3, 1, implicit $eflags, debug-location !117
bb.2:
successors: %bb.4
JMP_1 %bb.4, debug-location !120
bb.3:
successors: %bb.4
JMP_1 %bb.4, debug-location !117
bb.4:
successors: %bb.5, %bb.6
JCC_1 %bb.5, 1, implicit $eflags, debug-location !117
JMP_1 %bb.6, debug-location !117
bb.5:
RET 0, debug-location !117
bb.6:
RET 0, debug-location !117

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