[llvm] [AssignmentTracking] Skip large types in redundant debug info pruning (PR #74329)
Orlando Cazalet-Hyams via llvm-commits
llvm-commits at lists.llvm.org
Thu Dec 7 08:04:45 PST 2023
https://github.com/OCHyams updated https://github.com/llvm/llvm-project/pull/74329
>From 2af2bf6afbd341b43e0a529d8ad8c9433661e8e2 Mon Sep 17 00:00:00 2001
From: OCHyams <orlando.hyams at sony.com>
Date: Mon, 4 Dec 2023 12:08:08 +0000
Subject: [PATCH 1/3] [AssignemntTracking] Skip large types in redundant debug
info pruning
The pruning code uses a BitVector for varibles. BitVector supports sizes less
than max(uint32)-63, so skip equal and larger types. Fixes #74189 (crash
report).
The reason it's `max(uint32)-63` and not `max(uint32)` is because of
`BitVector::NumBitWords`:
unsigned NumBitWords(unsigned S) const {
return (S + BITWORD_SIZE-1) / BITWORD_SIZE;
}
The numerator evaluation yields an incorrect value when `S + BITWORD_SIZE`
wraps to `>= 1`
---
.../CodeGen/AssignmentTrackingAnalysis.cpp | 5 +-
.../assignment-tracking/X86/large-type.ll | 58 +++++++++++++++++++
2 files changed, 62 insertions(+), 1 deletion(-)
create mode 100644 llvm/test/DebugInfo/assignment-tracking/X86/large-type.ll
diff --git a/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp b/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp
index f00528023c91d..2349fadb1ea6d 100644
--- a/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp
+++ b/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp
@@ -2296,8 +2296,11 @@ removeRedundantDbgLocsUsingBackwardScan(const BasicBlock *BB,
getAggregate(FnVarLocs.getVariable(RIt->VariableID));
uint64_t SizeInBits = Aggr.first->getSizeInBits().value_or(0);
- if (SizeInBits == 0) {
+ const uint64_t MaxSize = std::numeric_limits<unsigned>::max() - 63;
+ if (SizeInBits == 0 || SizeInBits > MaxSize) {
// If the size is unknown (0) then keep this location def to be safe.
+ // Do the same for defs of very large variables, which can't be
+ // represented with a BitVector.
NewDefsReversed.push_back(*RIt);
continue;
}
diff --git a/llvm/test/DebugInfo/assignment-tracking/X86/large-type.ll b/llvm/test/DebugInfo/assignment-tracking/X86/large-type.ll
new file mode 100644
index 0000000000000..cebbc162fcb3a
--- /dev/null
+++ b/llvm/test/DebugInfo/assignment-tracking/X86/large-type.ll
@@ -0,0 +1,58 @@
+; RUN: llc %s -stop-after=finalize-isel -o - \
+; RUN: | FileCheck %s --implicit-check-not=DBG_
+
+;; Based on optimized IR from C source:
+;; int main () {
+;; char a1[__INT_MAX__];
+;; a1[__INT_MAX__ - 1] = 5;
+;; return a1[__INT_MAX__ - 1];
+;; }
+;;
+;; Check extremely large types don't cause a crash.
+; CHECK: DBG_VALUE 5, $noreg, ![[#]], !DIExpression(DW_OP_LLVM_fragment, 4294967280, 8)
+; CHECK: DBG_VALUE 6, $noreg, ![[#]], !DIExpression(DW_OP_LLVM_fragment, 0, 8)
+; CHECK: DBG_VALUE 7, $noreg, ![[#]], !DIExpression(DW_OP_LLVM_fragment, 0, 8)
+
+define dso_local i32 @main() local_unnamed_addr !dbg !10 {
+entry:
+;; FIXME: SROA currently creates incorrect fragments if bit_offset > max(u32),
+;; with and without assignment-tracking.
+ tail call void @llvm.dbg.value(metadata i8 5, metadata !15, metadata !DIExpression(DW_OP_LLVM_fragment, 4294967280, 8)), !dbg !20
+;; These two were inserted by hand.
+ tail call void @llvm.dbg.value(metadata i8 6, metadata !22, metadata !DIExpression(DW_OP_LLVM_fragment, 0, 8)), !dbg !20
+ tail call void @llvm.dbg.value(metadata i8 7, metadata !23, metadata !DIExpression(DW_OP_LLVM_fragment, 0, 8)), !dbg !20
+ ret i32 5, !dbg !21
+}
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3, !4, !5, !6, !7, !8}
+!llvm.ident = !{!9}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C11, file: !1, producer: "clang version 18.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "test.c", directory: "/")
+!2 = !{i32 7, !"Dwarf Version", i32 5}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !{i32 1, !"wchar_size", i32 4}
+!5 = !{i32 8, !"PIC Level", i32 2}
+!6 = !{i32 7, !"PIE Level", i32 2}
+!7 = !{i32 7, !"uwtable", i32 2}
+!8 = !{i32 7, !"debug-info-assignment-tracking", i1 true}
+!9 = !{!"clang version 18.0.0"}
+!10 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 3, type: !11, scopeLine: 4, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !14)
+!11 = !DISubroutineType(types: !12)
+!12 = !{!13}
+!13 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!14 = !{!15}
+!15 = !DILocalVariable(name: "a1", scope: !10, file: !1, line: 5, type: !16)
+!16 = !DICompositeType(tag: DW_TAG_array_type, baseType: !17, size: 17179869176, elements: !18)
+!17 = !DIBasicType(name: "char", size: 8, encoding: DW_ATE_signed_char)
+!18 = !{!19}
+!19 = !DISubrange(count: 2147483647)
+!20 = !DILocation(line: 0, scope: !10)
+!21 = !DILocation(line: 7, column: 3, scope: !10)
+!22 = !DILocalVariable(name: "a2", scope: !10, file: !1, line: 5, type: !16)
+!23 = !DILocalVariable(name: "a3", scope: !10, file: !1, line: 5, type: !16)
+!24 = !DICompositeType(tag: DW_TAG_array_type, baseType: !17, size: 4294967232, elements: !18)
+!25 = !DICompositeType(tag: DW_TAG_array_type, baseType: !17, size: 4294967233, elements: !18)
>From 6c8bb29c375b2f086326acd915d50821afaf6c8d Mon Sep 17 00:00:00 2001
From: OCHyams <orlando.hyams at sony.com>
Date: Tue, 5 Dec 2023 16:49:55 +0000
Subject: [PATCH 2/3] Bring cutoff down, track bytes rather than bits
---
.../CodeGen/AssignmentTrackingAnalysis.cpp | 31 +++++++++++--------
1 file changed, 18 insertions(+), 13 deletions(-)
diff --git a/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp b/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp
index 2349fadb1ea6d..583945118d2fc 100644
--- a/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp
+++ b/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp
@@ -2269,14 +2269,14 @@ static bool
removeRedundantDbgLocsUsingBackwardScan(const BasicBlock *BB,
FunctionVarLocsBuilder &FnVarLocs) {
bool Changed = false;
- SmallDenseMap<DebugAggregate, BitVector> VariableDefinedBits;
+ SmallDenseMap<DebugAggregate, BitVector> VariableDefinedBytes;
// Scan over the entire block, not just over the instructions mapped by
// FnVarLocs, because wedges in FnVarLocs may only be seperated by debug
// instructions.
for (const Instruction &I : reverse(*BB)) {
if (!isa<DbgVariableIntrinsic>(I)) {
// Sequence of consecutive defs ended. Clear map for the next one.
- VariableDefinedBits.clear();
+ VariableDefinedBytes.clear();
}
// Get the location defs that start just before this instruction.
@@ -2295,12 +2295,16 @@ removeRedundantDbgLocsUsingBackwardScan(const BasicBlock *BB,
DebugAggregate Aggr =
getAggregate(FnVarLocs.getVariable(RIt->VariableID));
uint64_t SizeInBits = Aggr.first->getSizeInBits().value_or(0);
+ uint64_t SizeInBytes = SizeInBits + 7 / 8;
- const uint64_t MaxSize = std::numeric_limits<unsigned>::max() - 63;
- if (SizeInBits == 0 || SizeInBits > MaxSize) {
+ // Cutoff for large variables to prevent expensive bitvector operations.
+ const uint64_t MaxSizeBytes = 2048;
+
+ if (SizeInBytes == 0 || SizeInBytes > MaxSizeBytes) {
// If the size is unknown (0) then keep this location def to be safe.
- // Do the same for defs of very large variables, which can't be
- // represented with a BitVector.
+ // Do the same for defs of large variables, which would be expensive
+ // to represent with a BitVector.
+ // FIXME: Don't use a BitVector.
NewDefsReversed.push_back(*RIt);
continue;
}
@@ -2308,23 +2312,24 @@ removeRedundantDbgLocsUsingBackwardScan(const BasicBlock *BB,
// Only keep this location definition if it is not fully eclipsed by
// other definitions in this wedge that come after it
- // Inert the bits the location definition defines.
+ // Inert the bytes the location definition defines.
auto InsertResult =
- VariableDefinedBits.try_emplace(Aggr, BitVector(SizeInBits));
+ VariableDefinedBytes.try_emplace(Aggr, BitVector(SizeInBytes));
bool FirstDefinition = InsertResult.second;
- BitVector &DefinedBits = InsertResult.first->second;
+ BitVector &DefinedBytes = InsertResult.first->second;
DIExpression::FragmentInfo Fragment =
RIt->Expr->getFragmentInfo().value_or(
DIExpression::FragmentInfo(SizeInBits, 0));
bool InvalidFragment = Fragment.endInBits() > SizeInBits;
+ uint64_t StartInBytes = Fragment.startInBits() + 7 / 8;
+ uint64_t EndInBytes = Fragment.endInBits() + 7 / 8;
- // If this defines any previously undefined bits, keep it.
+ // If this defines any previously undefined bytes, keep it.
if (FirstDefinition || InvalidFragment ||
- DefinedBits.find_first_unset_in(Fragment.startInBits(),
- Fragment.endInBits()) != -1) {
+ DefinedBytes.find_first_unset_in(StartInBytes, EndInBytes) != -1) {
if (!InvalidFragment)
- DefinedBits.set(Fragment.startInBits(), Fragment.endInBits());
+ DefinedBytes.set(StartInBytes, EndInBytes);
NewDefsReversed.push_back(*RIt);
continue;
}
>From eb75b663c1283f082ddb0ea726eefe04e561be61 Mon Sep 17 00:00:00 2001
From: OCHyams <orlando.hyams at sony.com>
Date: Thu, 7 Dec 2023 16:03:38 +0000
Subject: [PATCH 3/3] address comments
---
llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp b/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp
index 583945118d2fc..92e49ca5349a2 100644
--- a/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp
+++ b/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp
@@ -2295,7 +2295,7 @@ removeRedundantDbgLocsUsingBackwardScan(const BasicBlock *BB,
DebugAggregate Aggr =
getAggregate(FnVarLocs.getVariable(RIt->VariableID));
uint64_t SizeInBits = Aggr.first->getSizeInBits().value_or(0);
- uint64_t SizeInBytes = SizeInBits + 7 / 8;
+ uint64_t SizeInBytes = divideCeil(SizeInBits, 8);
// Cutoff for large variables to prevent expensive bitvector operations.
const uint64_t MaxSizeBytes = 2048;
@@ -2322,8 +2322,8 @@ removeRedundantDbgLocsUsingBackwardScan(const BasicBlock *BB,
RIt->Expr->getFragmentInfo().value_or(
DIExpression::FragmentInfo(SizeInBits, 0));
bool InvalidFragment = Fragment.endInBits() > SizeInBits;
- uint64_t StartInBytes = Fragment.startInBits() + 7 / 8;
- uint64_t EndInBytes = Fragment.endInBits() + 7 / 8;
+ uint64_t StartInBytes = Fragment.startInBits() / 8;
+ uint64_t EndInBytes = divideCeil(Fragment.endInBits(), 8);
// If this defines any previously undefined bytes, keep it.
if (FirstDefinition || InvalidFragment ||
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