11d3074267
Use the llvm flag `-pgo-function-entry-coverage` to create single byte "counters" to track functions coverage. This mode has significantly less size overhead in both code and data because * We mark a function as "covered" with a store instead of an increment which generally requires fewer assembly instructions * We use a single byte per function rather than 8 bytes per block The trade off of course is that this mode only tells you if a function has been covered. This is useful, for example, to detect dead code. When combined with debug info correlation [0] we are able to create an instrumented Clang binary that is only 150M (the vanilla Clang binary is 143M). That is an overhead of 7M (4.9%) compared to the default instrumentation (without value profiling) which has an overhead of 31M (21.7%). [0] https://groups.google.com/g/llvm-dev/c/r03Z6JoN7d4 Reviewed By: kyulee Differential Revision: https://reviews.llvm.org/D116180
35 lines
1.6 KiB
LLVM
35 lines
1.6 KiB
LLVM
; RUN: opt < %s -instrprof -debug-info-correlate -S | opt --O2 -S | FileCheck %s
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@__profn_foo = private constant [3 x i8] c"foo"
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; CHECK: @__profc_foo
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define void @_Z3foov() !dbg !12 {
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call void @llvm.instrprof.cover(i8* getelementptr inbounds ([3 x i8], [3 x i8]* @__profn_foo, i32 0, i32 0), i64 12345678, i32 1, i32 0)
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; CHECK: store i8 0, i8* getelementptr inbounds ([1 x i8], [1 x i8]* @__profc_foo
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ret void
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}
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declare void @llvm.instrprof.cover(i8*, i64, i32, i32)
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!llvm.dbg.cu = !{!0}
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!llvm.module.flags = !{!2, !3, !4, !5, !6, !7, !8, !9, !10}
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!llvm.ident = !{!11}
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!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 14.0.0", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
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!1 = !DIFile(filename: "debug-info-correlate-coverage.cpp", directory: "")
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!2 = !{i32 7, !"Dwarf Version", i32 4}
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!3 = !{i32 2, !"Debug Info Version", i32 3}
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!4 = !{i32 1, !"wchar_size", i32 4}
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!5 = !{i32 1, !"branch-target-enforcement", i32 0}
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!6 = !{i32 1, !"sign-return-address", i32 0}
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!7 = !{i32 1, !"sign-return-address-all", i32 0}
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!8 = !{i32 1, !"sign-return-address-with-bkey", i32 0}
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!9 = !{i32 7, !"uwtable", i32 1}
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!10 = !{i32 7, !"frame-pointer", i32 1}
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!11 = !{!"clang version 14.0.0"}
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!12 = distinct !DISubprogram(name: "foo", linkageName: "_Z3foov", scope: !13, file: !13, line: 1, type: !14, scopeLine: 1, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !16)
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!13 = !DIFile(filename: "debug-info-correlate-coverage.cpp", directory: "")
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!14 = !DISubroutineType(types: !15)
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!15 = !{null}
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!16 = !{}
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