ffd57408ef
Previous btf field relocation is always at assignment like
r1 = 4
which is converted from an ld_imm64 instruction.
This patch did an optimization such that relocation
instruction might be load/store/shift. Specically, the
following insns may also have relocation, except BPF_MOV:
LDB, LDH, LDW, LDD, STB, STH, STW, STD,
LDB32, LDH32, LDW32, STB32, STH32, STW32,
SLL, SRL, SRA
To accomplish this, a few BPF target specific
codegen only instructions are invented. They
are generated at backend BPF SimplifyPatchable phase,
which is at early llc phase when SSA form is available.
The new codegen only instructions will be converted to
real proper instructions at the codegen and BTF emission stage.
Note that, as revealed by a few tests, this optimization might
be actual generating more relocations:
Scenario 1:
if (...) {
... __builtin_preserve_field_info(arg->b2, 0) ...
} else {
... __builtin_preserve_field_info(arg->b2, 0) ...
}
Compiler could do CSE to only have one relocation. But if both
of the above is translated into codegen internal instructions,
the compiler will not be able to do that.
Scenario 2:
offset = ... __builtin_preserve_field_info(arg->b2, 0) ...
...
... offset ...
... offset ...
... offset ...
For whatever reason, the compiler might be temporarily do copy
propagation of the righthand of "offset" assignment like
... __builtin_preserve_field_info(arg->b2, 0) ...
... __builtin_preserve_field_info(arg->b2, 0) ...
and CSE will be able to deduplicate later.
But if these intrinsics are converted to BPF pseudo instructions,
they will not be able to get deduplicated.
I do not expect we have big instruction count difference.
It may actually reduce instruction count since now relocation
is in deeper insn dependency chain.
For example, for test offset-reloc-fieldinfo-2.ll, this patch
generates 7 instead of 6 relocations for non-alu32 mode, but it
actually reduced instruction count from 29 to 26.
Differential Revision: https://reviews.llvm.org/D71790
84 lines
4.3 KiB
LLVM
84 lines
4.3 KiB
LLVM
; RUN: llc -march=bpfel -filetype=asm -o - %s | FileCheck -check-prefixes=CHECK,CHECK-ALU64 %s
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; RUN: llc -march=bpfel -mattr=+alu32 -filetype=asm -o - %s | FileCheck -check-prefixes=CHECK,CHECK-ALU32 %s
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;
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; Source Code:
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; #define _(x) (__builtin_preserve_access_index(x))
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; struct s {int a; int b;};
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; int test(struct s *arg) { return *(const int *)_(&arg->b); }
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; Compiler flag to generate IR:
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; clang -target bpf -S -O2 -g -emit-llvm test.c
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%struct.s = type { i32, i32 }
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; Function Attrs: nounwind readonly
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define dso_local i32 @test(%struct.s* readonly %arg) local_unnamed_addr #0 !dbg !11 {
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entry:
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call void @llvm.dbg.value(metadata %struct.s* %arg, metadata !20, metadata !DIExpression()), !dbg !21
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%0 = tail call i32* @llvm.preserve.struct.access.index.p0i32.p0s_struct.ss(%struct.s* %arg, i32 1, i32 1), !dbg !22, !llvm.preserve.access.index !15
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%1 = load i32, i32* %0, align 4, !dbg !23, !tbaa !24
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ret i32 %1, !dbg !28
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}
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; CHECK-LABEL: test
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; CHECK-ALU64: r0 = *(u32 *)(r1 + 4)
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; CHECK-ALU32: w0 = *(u32 *)(r1 + 4)
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; CHECK: exit
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;
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; CHECK: .long 1 # BTF_KIND_STRUCT(id = 2)
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;
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; CHECK: .byte 115 # string offset=1
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; CHECK: .ascii ".text" # string offset=20
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; CHECK: .ascii "0:1" # string offset=26
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;
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; CHECK: .long 16 # FieldReloc
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; CHECK-NEXT: .long 20 # Field reloc section string offset=20
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; CHECK-NEXT: .long 1
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; CHECK-NEXT: .long .Ltmp{{[0-9]+}}
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; CHECK-NEXT: .long 2
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; CHECK-NEXT: .long 26
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; CHECK-NEXT: .long 0
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; Function Attrs: nounwind readnone
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declare i32* @llvm.preserve.struct.access.index.p0i32.p0s_struct.ss(%struct.s*, i32, i32) #1
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; Function Attrs: nounwind readnone speculatable willreturn
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declare void @llvm.dbg.value(metadata, metadata, metadata) #2
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attributes #0 = { nounwind readonly "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="all" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "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" }
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attributes #1 = { nounwind readnone }
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attributes #2 = { nounwind readnone speculatable willreturn }
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!llvm.dbg.cu = !{!0}
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!llvm.module.flags = !{!7, !8, !9}
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!llvm.ident = !{!10}
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!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 10.0.0 (https://github.com/llvm/llvm-project.git 6e353b4df3aa452ed4741a5e5caea02b1a876d8c)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !3, nameTableKind: None)
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!1 = !DIFile(filename: "test.c", directory: "/tmp/home/yhs/work/tests/core")
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!2 = !{}
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!3 = !{!4}
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!4 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !5, size: 64)
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!5 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !6)
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!6 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
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!7 = !{i32 2, !"Dwarf Version", i32 4}
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!8 = !{i32 2, !"Debug Info Version", i32 3}
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!9 = !{i32 1, !"wchar_size", i32 4}
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!10 = !{!"clang version 10.0.0 (https://github.com/llvm/llvm-project.git 6e353b4df3aa452ed4741a5e5caea02b1a876d8c)"}
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!11 = distinct !DISubprogram(name: "test", scope: !1, file: !1, line: 3, type: !12, scopeLine: 3, flags: DIFlagPrototyped, isDefinition: true, isOptimized: true, unit: !0, retainedNodes: !19)
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!12 = !DISubroutineType(types: !13)
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!13 = !{!6, !14}
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!14 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !15, size: 64)
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!15 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "s", file: !1, line: 2, size: 64, elements: !16)
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!16 = !{!17, !18}
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!17 = !DIDerivedType(tag: DW_TAG_member, name: "a", scope: !15, file: !1, line: 2, baseType: !6, size: 32)
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!18 = !DIDerivedType(tag: DW_TAG_member, name: "b", scope: !15, file: !1, line: 2, baseType: !6, size: 32, offset: 32)
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!19 = !{!20}
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!20 = !DILocalVariable(name: "arg", arg: 1, scope: !11, file: !1, line: 3, type: !14)
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!21 = !DILocation(line: 0, scope: !11)
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!22 = !DILocation(line: 3, column: 48, scope: !11)
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!23 = !DILocation(line: 3, column: 34, scope: !11)
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!24 = !{!25, !25, i64 0}
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!25 = !{!"int", !26, i64 0}
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!26 = !{!"omnipotent char", !27, i64 0}
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!27 = !{!"Simple C/C++ TBAA"}
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!28 = !DILocation(line: 3, column: 27, scope: !11)
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