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[BPF] do not generate unused local/global types

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The kernel currently has a limit for # of types to be 64KB and
the size of string subsection to be 64KB. A simple bcc tool
runqlat.py generates:
  . the size of ~33KB type section, roughly ~10K types
  . the size of ~17KB string section

The majority type is from the types referenced by local
variables in the bpf program. For example, the kernel "task_struct"
itself recursively brings in ~900 other types.
This patch did the following optimization to avoid generating
unused types:
  . do not generate types for local variables unless they are
    function arguments.
  . do not generate types for external globals.

If an external global is not used in the program, llvm
already removes it from IR, so global variable saving is
typical small. For runqlat.py, only one variable "llvm.used"
is the external global.

The types for locals and external globals can be added back
once there is a usage for them.

After the above optimization, the runqlat.py generates:
  . the size of ~1.5KB type section, roughtly 500 types
  . the size of ~0.7KB string section

UPDATE:
  resubmitted the patch after previous revert with
  the following fix:
  use Global.hasExternalLinkage() to test "external"
  linkage instead of using Global.getInitializer(),
  which will assert on external variables.

Signed-off-by: Yonghong Song <yhs@fb.com>
llvm-svn: 356234
This commit is contained in:
Yonghong Song 2019-03-15 05:51:25 +00:00
parent efb38e2269
commit c6159d464d
4 changed files with 296 additions and 7 deletions
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19
lib/Target/BPF/BTFDebug.cpp
View File

@ -658,12 +658,12 @@ void BTFDebug::beginFunctionImpl(const MachineFunction *MF) {
std::unordered_map<uint32_t, StringRef> FuncArgNames;
for (const DINode *DN : SP->getRetainedNodes()) {
if (const auto *DV = dyn_cast<DILocalVariable>(DN)) {
visitTypeEntry(DV->getType().resolve());
// Collect function arguments for subprogram func type.
uint32_t Arg = DV->getArg();
if (Arg)
if (Arg) {
visitTypeEntry(DV->getType().resolve());
FuncArgNames[Arg] = DV->getName();
}
}
}
@ -749,10 +749,15 @@ void BTFDebug::beginInstruction(const MachineInstr *MI) {
void BTFDebug::endModule() {
// Collect all types referenced by globals.
const Module *M = MMI->getModule();
for (const DICompileUnit *CUNode : M->debug_compile_units()) {
for (const auto *GVE : CUNode->getGlobalVariables()) {
DIGlobalVariable *GV = GVE->getVariable();
visitTypeEntry(GV->getType().resolve());
for (const GlobalVariable &Global : M->globals()) {
// Ignore external globals for now.
if (Global.hasExternalLinkage())
continue;
SmallVector<DIGlobalVariableExpression *, 1> GVs;
Global.getDebugInfo(GVs);
for (auto *GVE : GVs) {
visitTypeEntry(GVE->getVariable()->getType().resolve());
}
}

69
test/CodeGen/BPF/BTF/extern-global-var.ll Normal file
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@ -0,0 +1,69 @@
; RUN: llc -march=bpfel -filetype=asm -o - %s | FileCheck -check-prefixes=CHECK %s
; RUN: llc -march=bpfeb -filetype=asm -o - %s | FileCheck -check-prefixes=CHECK %s
; Source code:
; extern char a;
; int foo() { return a; }
; Compilation flag:
; clang -target bpf -O2 -g -S -emit-llvm test.c
@a = external dso_local local_unnamed_addr global i8, align 1
; Function Attrs: norecurse nounwind readonly
define dso_local i32 @foo() local_unnamed_addr #0 !dbg !7 {
%1 = load i8, i8* @a, align 1, !dbg !11, !tbaa !12
%2 = sext i8 %1 to i32, !dbg !11
ret i32 %2, !dbg !15
}
; CHECK: .section .BTF,"",@progbits
; CHECK-NEXT: .short 60319 # 0xeb9f
; CHECK-NEXT: .byte 1
; CHECK-NEXT: .byte 0
; CHECK-NEXT: .long 24
; CHECK-NEXT: .long 0
; CHECK-NEXT: .long 40
; CHECK-NEXT: .long 40
; CHECK-NEXT: .long 52
; CHECK-NEXT: .long 0 # BTF_KIND_FUNC_PROTO(id = 1)
; CHECK-NEXT: .long 218103808 # 0xd000000
; CHECK-NEXT: .long 2
; CHECK-NEXT: .long 44 # BTF_KIND_INT(id = 2)
; CHECK-NEXT: .long 16777216 # 0x1000000
; CHECK-NEXT: .long 4
; CHECK-NEXT: .long 16777248 # 0x1000020
; CHECK-NEXT: .long 48 # BTF_KIND_FUNC(id = 3)
; CHECK-NEXT: .long 201326592 # 0xc000000
; CHECK-NEXT: .long 1
; CHECK-NEXT: .byte 0 # string offset=0
; CHECK-NEXT: .ascii ".text" # string offset=1
; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii "/home/yhs/work/tests/llvm/bug/test.c" # string offset=7
; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii "int" # string offset=44
; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii "foo" # string offset=48
; CHECK-NEXT: .byte 0
attributes #0 = { norecurse nounwind readonly "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!3, !4, !5}
!llvm.ident = !{!6}
!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 8.0.20181009 ", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: None)
!1 = !DIFile(filename: "test.c", directory: "/home/yhs/work/tests/llvm/bug")
!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 8.0.20181009 "}
!7 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 2, type: !8, isLocal: false, isDefinition: true, scopeLine: 2, isOptimized: true, unit: !0, retainedNodes: !2)
!8 = !DISubroutineType(types: !9)
!9 = !{!10}
!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
!11 = !DILocation(line: 2, column: 20, scope: !7)
!12 = !{!13, !13, i64 0}
!13 = !{!"omnipotent char", !14, i64 0}
!14 = !{!"Simple C/C++ TBAA"}
!15 = !DILocation(line: 2, column: 13, scope: !7)

108
test/CodeGen/BPF/BTF/local-var.ll Normal file
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@ -0,0 +1,108 @@
; RUN: llc -march=bpfel -filetype=asm -o - %s | FileCheck -check-prefixes=CHECK %s
; RUN: llc -march=bpfeb -filetype=asm -o - %s | FileCheck -check-prefixes=CHECK %s
; Source code:
; int foo(char a) { volatile short b = 0; return b; }
; Compilation flag:
; clang -target bpf -O2 -g -S -emit-llvm test.c
; Function Attrs: nounwind
define dso_local i32 @foo(i8 signext) local_unnamed_addr #0 !dbg !7 {
%2 = alloca i16, align 2
call void @llvm.dbg.value(metadata i8 %0, metadata !13, metadata !DIExpression()), !dbg !17
%3 = bitcast i16* %2 to i8*, !dbg !18
call void @llvm.lifetime.start.p0i8(i64 2, i8* nonnull %3), !dbg !18
call void @llvm.dbg.declare(metadata i16* %2, metadata !14, metadata !DIExpression()), !dbg !19
store volatile i16 0, i16* %2, align 2, !dbg !19, !tbaa !20
%4 = load volatile i16, i16* %2, align 2, !dbg !24, !tbaa !20
%5 = sext i16 %4 to i32, !dbg !24
call void @llvm.lifetime.end.p0i8(i64 2, i8* nonnull %3), !dbg !25
ret i32 %5, !dbg !26
}
; CHECK: .section .BTF,"",@progbits
; CHECK-NEXT: .short 60319 # 0xeb9f
; CHECK-NEXT: .byte 1
; CHECK-NEXT: .byte 0
; CHECK-NEXT: .long 24
; CHECK-NEXT: .long 0
; CHECK-NEXT: .long 64
; CHECK-NEXT: .long 64
; CHECK-NEXT: .long 59
; CHECK-NEXT: .long 44 # BTF_KIND_INT(id = 1)
; CHECK-NEXT: .long 16777216 # 0x1000000
; CHECK-NEXT: .long 1
; CHECK-NEXT: .long 16777224 # 0x1000008
; CHECK-NEXT: .long 0 # BTF_KIND_FUNC_PROTO(id = 2)
; CHECK-NEXT: .long 218103809 # 0xd000001
; CHECK-NEXT: .long 3
; CHECK-NEXT: .long 49
; CHECK-NEXT: .long 1
; CHECK-NEXT: .long 51 # BTF_KIND_INT(id = 3)
; CHECK-NEXT: .long 16777216 # 0x1000000
; CHECK-NEXT: .long 4
; CHECK-NEXT: .long 16777248 # 0x1000020
; CHECK-NEXT: .long 55 # BTF_KIND_FUNC(id = 4)
; CHECK-NEXT: .long 201326592 # 0xc000000
; CHECK-NEXT: .long 2
; CHECK-NEXT: .byte 0 # string offset=0
; CHECK-NEXT: .ascii ".text" # string offset=1
; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii "/home/yhs/work/tests/llvm/bug/test.c" # string offset=7
; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii "char" # string offset=44
; CHECK-NEXT: .byte 0
; CHECK-NEXT: .byte 97 # string offset=49
; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii "int" # string offset=51
; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii "foo" # string offset=55
; CHECK-NEXT: .byte 0
; Function Attrs: nounwind readnone speculatable
declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
; Function Attrs: argmemonly nounwind
declare void @llvm.lifetime.start.p0i8(i64, i8* nocapture) #2
; Function Attrs: argmemonly nounwind
declare void @llvm.lifetime.end.p0i8(i64, i8* nocapture) #2
; Function Attrs: nounwind readnone speculatable
declare void @llvm.dbg.value(metadata, metadata, metadata) #1
attributes #0 = { nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
attributes #1 = { nounwind readnone speculatable }
attributes #2 = { argmemonly nounwind }
!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!3, !4, !5}
!llvm.ident = !{!6}
!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 8.0.20181009 ", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: None)
!1 = !DIFile(filename: "test.c", directory: "/home/yhs/work/tests/llvm/bug")
!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 8.0.20181009 "}
!7 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 1, type: !8, isLocal: false, isDefinition: true, scopeLine: 1, flags: DIFlagPrototyped, isOptimized: true, unit: !0, retainedNodes: !12)
!8 = !DISubroutineType(types: !9)
!9 = !{!10, !11}
!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
!11 = !DIBasicType(name: "char", size: 8, encoding: DW_ATE_signed_char)
!12 = !{!13, !14}
!13 = !DILocalVariable(name: "a", arg: 1, scope: !7, file: !1, line: 1, type: !11)
!14 = !DILocalVariable(name: "b", scope: !7, file: !1, line: 1, type: !15)
!15 = !DIDerivedType(tag: DW_TAG_volatile_type, baseType: !16)
!16 = !DIBasicType(name: "short", size: 16, encoding: DW_ATE_signed)
!17 = !DILocation(line: 1, column: 14, scope: !7)
!18 = !DILocation(line: 1, column: 19, scope: !7)
!19 = !DILocation(line: 1, column: 34, scope: !7)
!20 = !{!21, !21, i64 0}
!21 = !{!"short", !22, i64 0}
!22 = !{!"omnipotent char", !23, i64 0}
!23 = !{!"Simple C/C++ TBAA"}
!24 = !DILocation(line: 1, column: 49, scope: !7)
!25 = !DILocation(line: 1, column: 52, scope: !7)
!26 = !DILocation(line: 1, column: 42, scope: !7)

107
test/CodeGen/BPF/BTF/static-var.ll Normal file
View File

@ -0,0 +1,107 @@
; RUN: llc -march=bpfel -filetype=asm -o - %s | FileCheck -check-prefixes=CHECK %s
; RUN: llc -march=bpfeb -filetype=asm -o - %s | FileCheck -check-prefixes=CHECK %s
; Source code:
; static volatile char a;
; int foo() {
; static volatile short b;
; return a + b;
; }
; Compilation flag:
; clang -target bpf -O2 -g -S -emit-llvm test.c
@foo.b = internal global i16 0, align 2, !dbg !0
@a = internal global i8 0, align 1, !dbg !10
; Function Attrs: norecurse nounwind
define dso_local i32 @foo() local_unnamed_addr #0 !dbg !2 {
%1 = load volatile i8, i8* @a, align 1, !dbg !20, !tbaa !21
%2 = sext i8 %1 to i32, !dbg !20
%3 = load volatile i16, i16* @foo.b, align 2, !dbg !24, !tbaa !25
%4 = sext i16 %3 to i32, !dbg !24
%5 = add nsw i32 %4, %2, !dbg !27
ret i32 %5, !dbg !28
}
; CHECK: .section .BTF,"",@progbits
; CHECK-NEXT: .short 60319 # 0xeb9f
; CHECK-NEXT: .byte 1
; CHECK-NEXT: .byte 0
; CHECK-NEXT: .long 24
; CHECK-NEXT: .long 0
; CHECK-NEXT: .long 96
; CHECK-NEXT: .long 96
; CHECK-NEXT: .long 63
; CHECK-NEXT: .long 0 # BTF_KIND_FUNC_PROTO(id = 1)
; CHECK-NEXT: .long 218103808 # 0xd000000
; CHECK-NEXT: .long 2
; CHECK-NEXT: .long 44 # BTF_KIND_INT(id = 2)
; CHECK-NEXT: .long 16777216 # 0x1000000
; CHECK-NEXT: .long 4
; CHECK-NEXT: .long 16777248 # 0x1000020
; CHECK-NEXT: .long 48 # BTF_KIND_FUNC(id = 3)
; CHECK-NEXT: .long 201326592 # 0xc000000
; CHECK-NEXT: .long 1
; CHECK-NEXT: .long 0 # BTF_KIND_VOLATILE(id = 4)
; CHECK-NEXT: .long 150994944 # 0x9000000
; CHECK-NEXT: .long 5
; CHECK-NEXT: .long 52 # BTF_KIND_INT(id = 5)
; CHECK-NEXT: .long 16777216 # 0x1000000
; CHECK-NEXT: .long 2
; CHECK-NEXT: .long 16777232 # 0x1000010
; CHECK-NEXT: .long 0 # BTF_KIND_VOLATILE(id = 6)
; CHECK-NEXT: .long 150994944 # 0x9000000
; CHECK-NEXT: .long 7
; CHECK-NEXT: .long 58 # BTF_KIND_INT(id = 7)
; CHECK-NEXT: .long 16777216 # 0x1000000
; CHECK-NEXT: .long 1
; CHECK-NEXT: .long 16777224 # 0x1000008
; CHECK-NEXT: .byte 0 # string offset=0
; CHECK-NEXT: .ascii ".text" # string offset=1
; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii "/home/yhs/work/tests/llvm/bug/test.c" # string offset=7
; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii "int" # string offset=44
; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii "foo" # string offset=48
; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii "short" # string offset=52
; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii "char" # string offset=58
; CHECK-NEXT: .byte 0
attributes #0 = { norecurse nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
!llvm.dbg.cu = !{!7}
!llvm.module.flags = !{!16, !17, !18}
!llvm.ident = !{!19}
!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
!1 = distinct !DIGlobalVariable(name: "b", scope: !2, file: !3, line: 3, type: !14, isLocal: true, isDefinition: true)
!2 = distinct !DISubprogram(name: "foo", scope: !3, file: !3, line: 2, type: !4, isLocal: false, isDefinition: true, scopeLine: 2, isOptimized: true, unit: !7, retainedNodes: !8)
!3 = !DIFile(filename: "test.c", directory: "/home/yhs/work/tests/llvm/bug")
!4 = !DISubroutineType(types: !5)
!5 = !{!6}
!6 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
!7 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 8.0.20181009 ", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !8, globals: !9, nameTableKind: None)
!8 = !{}
!9 = !{!0, !10}
!10 = !DIGlobalVariableExpression(var: !11, expr: !DIExpression())
!11 = distinct !DIGlobalVariable(name: "a", scope: !7, file: !3, line: 1, type: !12, isLocal: true, isDefinition: true)
!12 = !DIDerivedType(tag: DW_TAG_volatile_type, baseType: !13)
!13 = !DIBasicType(name: "char", size: 8, encoding: DW_ATE_signed_char)
!14 = !DIDerivedType(tag: DW_TAG_volatile_type, baseType: !15)
!15 = !DIBasicType(name: "short", size: 16, encoding: DW_ATE_signed)
!16 = !{i32 2, !"Dwarf Version", i32 4}
!17 = !{i32 2, !"Debug Info Version", i32 3}
!18 = !{i32 1, !"wchar_size", i32 4}
!19 = !{!"clang version 8.0.20181009 "}
!20 = !DILocation(line: 4, column: 10, scope: !2)
!21 = !{!22, !22, i64 0}
!22 = !{!"omnipotent char", !23, i64 0}
!23 = !{!"Simple C/C++ TBAA"}
!24 = !DILocation(line: 4, column: 14, scope: !2)
!25 = !{!26, !26, i64 0}
!26 = !{!"short", !22, i64 0}
!27 = !DILocation(line: 4, column: 12, scope: !2)
!28 = !DILocation(line: 4, column: 3, scope: !2)