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DebugInfo: Improve debug location merging

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Fix a set of related bugs:

* Considering two locations as equivalent when their lines are the same
but their scopes are different causes erroneous debug info that
attributes a commoned call to be attributed to one of the two calls it
was commoned from.

* The previous code to compute a new location's scope was inaccurate and
would use the inlinedAt that was the /parent/ of the inlinedAt that is
the nearest common one, and also used that parent scope instead of the
nearest common scope.

* Not generating new locations generally seemed like a lower quality
choice

There was some risk that generating more new locations could hurt object
size by making more fine grained line table entries, but it looks like
that was offset by the decrease in line table (& address & ranges) size
caused by more accurately computing the scope - which likely lead to
fewer range entries (more contiguous ranges) & reduced size that way.

All up with these changes I saw minor reductions (-1.21%, -1.77%) in
.rela.debug_ranges and .rela.debug_addr (in a fission, compressed debug
info build) as well as other minor size changes (generally reductinos)
across the board (-1.32% debug_info.dwo, -1.28% debug_loc.dwo). Measured
in an optimized (-O2) build of the clang binary.

If you are investigating a size regression in an optimized debug builds,
this is certainly a patch to look into - and I'd be happy to look into
any major regressions found & see what we can do to address them.

llvm-svn: 340583
This commit is contained in:
David Blaikie 2018-08-23 22:35:58 +00:00
parent 4ce3f8eb03
commit 78e228c700
5 changed files with 130 additions and 35 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
include/llvm/IR/DebugInfoMetadata.h
View File

@ -1479,19 +1479,6 @@ public:
return getScope();
}
/// Check whether this can be discriminated from another location.
///
/// Check \c this can be discriminated from \c RHS in a linetable entry.
/// Scope and inlined-at chains are not recorded in the linetable, so they
/// cannot be used to distinguish basic blocks.
bool canDiscriminate(const DILocation &RHS) const {
return getLine() != RHS.getLine() ||
getColumn() != RHS.getColumn() ||
getDiscriminator() != RHS.getDiscriminator() ||
getFilename() != RHS.getFilename() ||
getDirectory() != RHS.getDirectory();
}
/// Get the DWARF discriminator.
///
/// DWARF discriminators distinguish identical file locations between
@ -1539,8 +1526,6 @@ public:
/// discriminator.
inline const DILocation *cloneWithDuplicationFactor(unsigned DF) const;
enum { NoGeneratedLocation = false, WithGeneratedLocation = true };
/// When two instructions are combined into a single instruction we also
/// need to combine the original locations into a single location.
///
@ -1555,9 +1540,8 @@ public:
///
/// \p GenerateLocation: Whether the merged location can be generated when
/// \p LocA and \p LocB differ.
static const DILocation *
getMergedLocation(const DILocation *LocA, const DILocation *LocB,
bool GenerateLocation = NoGeneratedLocation);
static const DILocation *getMergedLocation(const DILocation *LocA,
const DILocation *LocB);
/// Returns the base discriminator for a given encoded discriminator \p D.
static unsigned getBaseDiscriminatorFromDiscriminator(unsigned D) {

3
lib/IR/DebugInfo.cpp
View File

@ -690,8 +690,7 @@ unsigned llvm::getDebugMetadataVersionFromModule(const Module &M) {
void Instruction::applyMergedLocation(const DILocation *LocA,
const DILocation *LocB) {
setDebugLoc(DILocation::getMergedLocation(LocA, LocB,
DILocation::WithGeneratedLocation));
setDebugLoc(DILocation::getMergedLocation(LocA, LocB));
}
//===----------------------------------------------------------------------===//

40
lib/IR/DebugInfoMetadata.cpp
View File

@ -14,7 +14,7 @@
#include "llvm/IR/DebugInfoMetadata.h"
#include "LLVMContextImpl.h"
#include "MetadataImpl.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/StringSwitch.h"
#include "llvm/IR/DIBuilder.h"
#include "llvm/IR/Function.h"
@ -69,28 +69,40 @@ DILocation *DILocation::getImpl(LLVMContext &Context, unsigned Line,
}
const DILocation *DILocation::getMergedLocation(const DILocation *LocA,
const DILocation *LocB,
bool GenerateLocation) {
const DILocation *LocB) {
if (!LocA || !LocB)
return nullptr;
if (LocA == LocB || !LocA->canDiscriminate(*LocB))
if (LocA == LocB)
return LocA;
if (!GenerateLocation)
return nullptr;
SmallPtrSet<DILocation *, 5> InlinedLocationsA;
for (DILocation *L = LocA->getInlinedAt(); L; L = L->getInlinedAt())
InlinedLocationsA.insert(L);
const DILocation *Result = LocB;
for (DILocation *L = LocB->getInlinedAt(); L; L = L->getInlinedAt()) {
Result = L;
if (InlinedLocationsA.count(L))
break;
SmallSet<std::pair<DIScope *, DILocation *>, 5> Locations;
DIScope *S = LocA->getScope();
DILocation *L = LocA->getInlinedAt();
while (S) {
Locations.insert(std::make_pair(S, L));
S = S->getScope().resolve();
if (!S && L) {
S = L->getScope();
L = L->getInlinedAt();
}
}
return DILocation::get(Result->getContext(), 0, 0, Result->getScope(),
Result->getInlinedAt());
const DILocation *Result = LocB;
S = LocB->getScope();
L = LocB->getInlinedAt();
while (S) {
if (Locations.count(std::make_pair(S, L)))
break;
S = S->getScope().resolve();
if (!S && L) {
S = L->getScope();
L = L->getInlinedAt();
}
}
return DILocation::get(Result->getContext(), 0, 0, S, L);
}
DINode::DIFlags DINode::getFlag(StringRef Flag) {

2
test/DebugInfo/COFF/local-variables.ll
View File

@ -60,7 +60,7 @@
; ASM: leaq 36(%rsp), %rcx
; ASM: [[else_end:\.Ltmp.*]]:
; ASM: .LBB0_3: # %if.end
; ASM: .cv_loc 0 1 17 1 # t.cpp:17:1
; ASM: .cv_loc 0 1 0 0 # t.cpp:0:0
; ASM: callq capture
; ASM: nop
; ASM: addq $56, %rsp

100
test/DebugInfo/X86/merge_inlined_loc.ll Normal file
View File

@ -0,0 +1,100 @@
; RUN: llc %s -mtriple=x86_64-unknown-unknown -o - | FileCheck %s
; Generated with "clang -g -c -emit-llvm -S -O3"
; This will test several features of merging debug locations. Importantly,
; locations with the same source line but different scopes should be merged to
; a line zero location at the nearest common scope and inlining. The location
; of the single call to "common" (the two calls are collapsed together by
; BranchFolding) should be attributed to line zero inside the wrapper2 inlined
; scope within f1.
; void common();
; inline void wrapper() { common(); }
; extern bool b;
; void sink();
; inline void wrapper2() {
; if (b) {
; sink();
; wrapper();
; } else
; wrapper();
; }
; void f1() { wrapper2(); }
; Ensure there is only one inlined_subroutine (for wrapper2, none for wrapper)
; & that its address range includes the call to 'common'.
; CHECK: jmp _Z6commonv
; CHECK-NEXT: [[LABEL:.*]]:
; CHECK: .section .debug_info
; CHECK: DW_TAG_subprogram
; CHECK: DW_TAG_subprogram
; CHECK-NOT: {{DW_TAG\|End Of Children}}
; CHECK: DW_TAG_inlined_subroutine
; CHECK-NOT: {{DW_TAG\|End Of Children}}
; CHECK: [[LABEL]]-{{.*}} DW_AT_high_pc
; CHECK-NOT: DW_TAG
@b = external dso_local local_unnamed_addr global i8, align 1
; Function Attrs: uwtable
define dso_local void @_Z2f1v() local_unnamed_addr !dbg !7 {
entry:
%0 = load i8, i8* @b, align 1, !dbg !10, !tbaa !14, !range !18
%tobool.i = icmp eq i8 %0, 0, !dbg !10
br i1 %tobool.i, label %if.else.i, label %if.then.i, !dbg !19
if.then.i: ; preds = %entry
tail call void @_Z4sinkv(), !dbg !20
tail call void @_Z6commonv(), !dbg !22
br label %_Z8wrapper2v.exit, !dbg !25
if.else.i: ; preds = %entry
tail call void @_Z6commonv(), !dbg !26
br label %_Z8wrapper2v.exit
_Z8wrapper2v.exit: ; preds = %if.then.i, %if.else.i
ret void, !dbg !28
}
declare dso_local void @_Z4sinkv() local_unnamed_addr
declare dso_local void @_Z6commonv() local_unnamed_addr
!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!3, !4, !5}
!llvm.ident = !{!6}
!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 8.0.0 (trunk 340559) (llvm/trunk 340572)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: None)
!1 = !DIFile(filename: "merge_loc.cpp", directory: "/usr/local/google/home/blaikie/dev/scratch")
!2 = !{}
!3 = !{i32 2, !"Dwarf Version", i32 4}
!4 = !{i32 2, !"Debug Info Version", i32 3}
!5 = !{i32 1, !"wchar_size", i32 4}
!6 = !{!"clang version 8.0.0 (trunk 340559) (llvm/trunk 340572)"}
!7 = distinct !DISubprogram(name: "f1", linkageName: "_Z2f1v", scope: !1, file: !1, line: 12, type: !8, isLocal: false, isDefinition: true, scopeLine: 12, flags: DIFlagPrototyped, isOptimized: true, unit: !0, retainedNodes: !2)
!8 = !DISubroutineType(types: !9)
!9 = !{null}
!10 = !DILocation(line: 6, column: 7, scope: !11, inlinedAt: !13)
!11 = distinct !DILexicalBlock(scope: !12, file: !1, line: 6, column: 7)
!12 = distinct !DISubprogram(name: "wrapper2", linkageName: "_Z8wrapper2v", scope: !1, file: !1, line: 5, type: !8, isLocal: false, isDefinition: true, scopeLine: 5, flags: DIFlagPrototyped, isOptimized: true, unit: !0, retainedNodes: !2)
!13 = distinct !DILocation(line: 13, column: 3, scope: !7)
!14 = !{!15, !15, i64 0}
!15 = !{!"bool", !16, i64 0}
!16 = !{!"omnipotent char", !17, i64 0}
!17 = !{!"Simple C++ TBAA"}
!18 = !{i8 0, i8 2}
!19 = !DILocation(line: 6, column: 7, scope: !12, inlinedAt: !13)
!20 = !DILocation(line: 7, column: 5, scope: !21, inlinedAt: !13)
!21 = distinct !DILexicalBlock(scope: !11, file: !1, line: 6, column: 10)
!22 = !DILocation(line: 2, column: 25, scope: !23, inlinedAt: !24)
!23 = distinct !DISubprogram(name: "wrapper", linkageName: "_Z7wrapperv", scope: !1, file: !1, line: 2, type: !8, isLocal: false, isDefinition: true, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: true, unit: !0, retainedNodes: !2)
!24 = distinct !DILocation(line: 8, column: 5, scope: !21, inlinedAt: !13)
!25 = !DILocation(line: 9, column: 3, scope: !21, inlinedAt: !13)
!26 = !DILocation(line: 2, column: 25, scope: !23, inlinedAt: !27)
!27 = distinct !DILocation(line: 10, column: 5, scope: !11, inlinedAt: !13)
!28 = !DILocation(line: 14, column: 1, scope: !7)