llvm-dwarfdump: Add an option to collect debug info quality metrics.

At the last LLVM dev meeting we had a debug info for optimized code
BoF session. In that session I presented some graphs that showed how
the quality of the debug info produced by LLVM changed over the last
couple of years. This is a cleaned up version of the patch I used to
collect the this data. It is implemented as an extension of
llvm-dwarfdump, adding a new --statistics option. The intended
use-case is to automatically run this on the debug info produced by,
e.g., our bots, to identify eyebrow-raising changes or regressions
introduced by new transformations that we could act on.

In the current form, two kinds of data are being collected:

- The number of variables that have a debug location versus the number
  of variables in total (this takes into account inlined instances of
  the same function, so if a variable is completely missing form only
  one instance it will be found).

- The PC range covered by variable location descriptions versus the PC
  range of all variables' containing lexical scopes.

The output format is versioned and extensible, so I'm looking forward
to both bug fixes and ideas for other data that would be interesting
to track.

Differential Revision: https://reviews.llvm.org/D36627

llvm-svn: 315101

1 files changed, 134 insertions, 0 deletions

diff --git a/llvm/test/tools/llvm-dwarfdump/X86/statistics.ll b/llvm/test/tools/llvm-dwarfdump/X86/statistics.ll
new file mode 100644
index 00000000000..bc955453716
--- /dev/null
+++ b/llvm/test/tools/llvm-dwarfdump/X86/statistics.ll
@@ -0,0 +1,134 @@
+; RUN: llc -O0 %s -o - -filetype=obj \
+; RUN:   | llvm-dwarfdump -statistics - | FileCheck %s
+
+; int GlobalConst = 42;
+; int Global;
+;
+; struct S {
+;   static const int constant = 24;
+; } s;
+;
+; int __attribute__((always_inline)) square(int i) { return i * i; }
+; int cube(int i) {
+;   int squared = square(i);
+;   return squared*i;
+; }
+
+; GlobalConst,Global,s,s.constant,square::i,cube::i,cube::squared
+; CHECK: "unique source variables":7
+; +1 extra inline i.
+; CHECK: "source variables":8
+; -1 square::i
+; CHECK: "variables with location":7
+; CHECK: "scope bytes total":[[BYTES:[0-9]+]]
+; Because of the dbg.value in the middle of the function, the pc range coverage
+; must be below 100%.
+; CHECK-NOT: "scope bytes covered":0
+; CHECK-NOT "scope bytes covered":[[BYTES]]
+; CHECK: "scope bytes covered":
+
+; ModuleID = '/tmp/quality.cpp'
+source_filename = "/tmp/quality.cpp"
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.12.0"
+
+%struct.S = type { i8 }
+
+@GlobalConst = global i32 42, align 4, !dbg !0
+@Global = global i32 0, align 4, !dbg !6
+@s = global %struct.S zeroinitializer, align 1, !dbg !9
+
+; Function Attrs: alwaysinline nounwind ssp uwtable
+define i32 @_Z6squarei(i32 %i) #0 !dbg !20 {
+entry:
+  %i.addr = alloca i32, align 4
+  store i32 %i, i32* %i.addr, align 4
+  ; Modified to loose debug info for i here.
+  call void @llvm.dbg.declare(metadata i32* undef, metadata !23, metadata !24), !dbg !25
+  %0 = load i32, i32* %i.addr, align 4, !dbg !26
+  %1 = load i32, i32* %i.addr, align 4, !dbg !27
+  %mul = mul nsw i32 %0, %1, !dbg !28
+  ret i32 %mul, !dbg !29
+}
+
+; Function Attrs: nounwind readnone speculatable
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
+declare void @llvm.dbg.value(metadata, metadata, metadata) #1
+
+; Function Attrs: noinline nounwind optnone ssp uwtable
+define i32 @_Z4cubei(i32 %i) #2 !dbg !30 {
+entry:
+  %i.addr.i = alloca i32, align 4
+  call void @llvm.dbg.declare(metadata i32* %i.addr.i, metadata !23, metadata !24), !dbg !31
+  %i.addr = alloca i32, align 4
+  %squared = alloca i32, align 4
+  store i32 %i, i32* %i.addr, align 4
+  call void @llvm.dbg.declare(metadata i32* %i.addr, metadata !33, metadata !24), !dbg !34
+  %0 = load i32, i32* %i.addr, align 4, !dbg !37
+  store i32 %0, i32* %i.addr.i, align 4
+  %1 = load i32, i32* %i.addr.i, align 4, !dbg !38
+  %2 = load i32, i32* %i.addr.i, align 4, !dbg !39
+  %mul.i = mul nsw i32 %1, %2, !dbg !40
+  ; Modified to cover only about 50% of the lexical scope.
+  call void @llvm.dbg.value(metadata i32 %mul.i, metadata !35, metadata !24), !dbg !36
+  store i32 %mul.i, i32* %squared, align 4, !dbg !36
+  %3 = load i32, i32* %squared, align 4, !dbg !41
+  call void @llvm.dbg.value(metadata i32 %3, metadata !35, metadata !24), !dbg !36
+  %4 = load i32, i32* %i.addr, align 4, !dbg !42
+  %mul = mul nsw i32 %3, %4, !dbg !43
+  ret i32 %mul, !dbg !44
+}
+
+attributes #0 = { alwaysinline nounwind ssp uwtable }
+attributes #1 = { nounwind readnone speculatable }
+attributes #2 = { noinline nounwind optnone ssp uwtable }
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!15, !16, !17, !18}
+!llvm.ident = !{!19}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "GlobalConst", scope: !2, file: !3, line: 1, type: !8, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, producer: "clang version 6.0.0 (trunk 310529) (llvm/trunk 310534)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5)
+!3 = !DIFile(filename: "/tmp/quality.cpp", directory: "/Volumes/Data/llvm")
+!4 = !{}
+!5 = !{!0, !6, !9}
+!6 = !DIGlobalVariableExpression(var: !7, expr: !DIExpression())
+!7 = distinct !DIGlobalVariable(name: "Global", scope: !2, file: !3, line: 2, type: !8, isLocal: false, isDefinition: true)
+!8 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!9 = !DIGlobalVariableExpression(var: !10, expr: !DIExpression())
+!10 = distinct !DIGlobalVariable(name: "s", scope: !2, file: !3, line: 6, type: !11, isLocal: false, isDefinition: true)
+!11 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "S", file: !3, line: 4, size: 8, elements: !12, identifier: "_ZTS1S")
+!12 = !{!13}
+!13 = !DIDerivedType(tag: DW_TAG_member, name: "constant", scope: !11, file: !3, line: 5, baseType: !14, flags: DIFlagStaticMember, extraData: i32 24)
+!14 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !8)
+!15 = !{i32 2, !"Dwarf Version", i32 4}
+!16 = !{i32 2, !"Debug Info Version", i32 3}
+!17 = !{i32 1, !"wchar_size", i32 4}
+!18 = !{i32 7, !"PIC Level", i32 2}
+!19 = !{!"clang version 6.0.0 (trunk 310529) (llvm/trunk 310534)"}
+!20 = distinct !DISubprogram(name: "square", linkageName: "_Z6squarei", scope: !3, file: !3, line: 8, type: !21, isLocal: false, isDefinition: true, scopeLine: 8, flags: DIFlagPrototyped, isOptimized: false, unit: !2, variables: !4)
+!21 = !DISubroutineType(types: !22)
+!22 = !{!8, !8}
+!23 = !DILocalVariable(name: "i", arg: 1, scope: !20, file: !3, line: 8, type: !8)
+!24 = !DIExpression()
+!25 = !DILocation(line: 8, column: 47, scope: !20)
+!26 = !DILocation(line: 8, column: 59, scope: !20)
+!27 = !DILocation(line: 8, column: 63, scope: !20)
+!28 = !DILocation(line: 8, column: 61, scope: !20)
+!29 = !DILocation(line: 8, column: 52, scope: !20)
+!30 = distinct !DISubprogram(name: "cube", linkageName: "_Z4cubei", scope: !3, file: !3, line: 9, type: !21, isLocal: false, isDefinition: true, scopeLine: 9, flags: DIFlagPrototyped, isOptimized: false, unit: !2, variables: !4)
+!31 = !DILocation(line: 8, column: 47, scope: !20, inlinedAt: !32)
+!32 = distinct !DILocation(line: 10, column: 17, scope: !30)
+!33 = !DILocalVariable(name: "i", arg: 1, scope: !30, file: !3, line: 9, type: !8)
+!34 = !DILocation(line: 9, column: 14, scope: !30)
+!35 = !DILocalVariable(name: "squared", scope: !30, file: !3, line: 10, type: !8)
+!36 = !DILocation(line: 10, column: 7, scope: !30)
+!37 = !DILocation(line: 10, column: 24, scope: !30)
+!38 = !DILocation(line: 8, column: 59, scope: !20, inlinedAt: !32)
+!39 = !DILocation(line: 8, column: 63, scope: !20, inlinedAt: !32)
+!40 = !DILocation(line: 8, column: 61, scope: !20, inlinedAt: !32)
+!41 = !DILocation(line: 11, column: 10, scope: !30)
+!42 = !DILocation(line: 11, column: 18, scope: !30)
+!43 = !DILocation(line: 11, column: 17, scope: !30)
+!44 = !DILocation(line: 11, column: 3, scope: !30)