forked from OSchip/llvm-project
[BPF] Fix a bug in BPFMISimplifyPatchable pass
LLVM BPF pass SimplifyPatchable is used to do necessary
code conversion for CO-RE operations. When studying bpf
selftest 'exhandler', I found a corner case not handled properly.
The following is the C code, modified from original 'exhandler'
code.
int g;
int test(struct t1 *p) {
struct t2 *q = p->q;
if (q)
return 0;
struct t3 *f = q->f;
if (!f) g = 5;
return 0;
}
For code:
struct t3 *f = q->f;
if (!f) ...
The IR before BPFMISimplifyPatchable pass looks like:
%5:gpr = LD_imm64 @"llvm.t2:0:8$0:1"
%6:gpr = LDD killed %5:gpr, 0
%7:gpr = LDD killed %6:gpr, 0
JNE_ri killed %7:gpr, 0, %bb.3
JMP %bb.2
Note that compiler knows q = 0 based dataflow and value analysis.
The correct generated code after the pass should be
%5:gpr = LD_imm64 @"llvm.t2:0:8$0:1"
%7:gpr = LDD killed %5:gpr, 0
JNE_ri killed %7:gpr, 0, %bb.3
JMP %bb.2
But the current implementation did further optimization for the
above code and generates
%5:gpr = LD_imm64 @"llvm.t2:0:8$0:1"
JNE_ri killed %5:gpr, 0, %bb.3
JMP %bb.2
which is incorrect.
This patch added a cache to remember those load insns not associated
with CO-RE offset value and will skip these load insns during
transformation.
Differential Revision: https://reviews.llvm.org/D123883
This commit is contained in:
Peter Klausler
Yonghong Song
parent
6b0bed7ea5
commit
497a5f0415
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@ -35,6 +35,7 @@
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#include "llvm/CodeGen/MachineInstrBuilder.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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#include "llvm/Support/Debug.h"
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#include <set>
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using namespace llvm;
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@ -53,9 +54,12 @@ struct BPFMISimplifyPatchable : public MachineFunctionPass {
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}
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private:
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std::set<MachineInstr *> SkipInsts;
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// Initialize class variables.
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void initialize(MachineFunction &MFParm);
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bool isLoadInst(unsigned Opcode);
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bool removeLD();
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void processCandidate(MachineRegisterInfo *MRI, MachineBasicBlock &MBB,
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MachineInstr &MI, Register &SrcReg, Register &DstReg,
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@ -89,6 +93,12 @@ void BPFMISimplifyPatchable::initialize(MachineFunction &MFParm) {
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LLVM_DEBUG(dbgs() << "*** BPF simplify patchable insts pass ***\n\n");
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}
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bool BPFMISimplifyPatchable::isLoadInst(unsigned Opcode) {
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return Opcode == BPF::LDD || Opcode == BPF::LDW || Opcode == BPF::LDH ||
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Opcode == BPF::LDB || Opcode == BPF::LDW32 || Opcode == BPF::LDH32 ||
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Opcode == BPF::LDB32;
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}
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void BPFMISimplifyPatchable::checkADDrr(MachineRegisterInfo *MRI,
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MachineOperand *RelocOp, const GlobalValue *GVal) {
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const MachineInstr *Inst = RelocOp->getParent();
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@ -230,6 +240,11 @@ void BPFMISimplifyPatchable::processDstReg(MachineRegisterInfo *MRI,
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void BPFMISimplifyPatchable::processInst(MachineRegisterInfo *MRI,
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MachineInstr *Inst, MachineOperand *RelocOp, const GlobalValue *GVal) {
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unsigned Opcode = Inst->getOpcode();
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if (isLoadInst(Opcode)) {
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SkipInsts.insert(Inst);
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return;
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}
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if (Opcode == BPF::ADD_rr)
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checkADDrr(MRI, RelocOp, GVal);
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else if (Opcode == BPF::SLL_rr)
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@ -254,10 +269,10 @@ bool BPFMISimplifyPatchable::removeLD() {
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}
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// Ensure the register format is LOAD <reg>, <reg>, 0
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if (MI.getOpcode() != BPF::LDD && MI.getOpcode() != BPF::LDW &&
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MI.getOpcode() != BPF::LDH && MI.getOpcode() != BPF::LDB &&
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MI.getOpcode() != BPF::LDW32 && MI.getOpcode() != BPF::LDH32 &&
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MI.getOpcode() != BPF::LDB32)
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if (!isLoadInst(MI.getOpcode()))
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continue;
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if (SkipInsts.find(&MI) != SkipInsts.end())
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continue;
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if (!MI.getOperand(0).isReg() || !MI.getOperand(1).isReg())
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@ -0,0 +1,136 @@
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; RUN: llc -O2 -march=bpf -mcpu=v3 < %s | FileCheck %s
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; Source code:
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; struct t3 {
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; int i;
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; } __attribute__((preserve_access_index));
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; struct t2 {
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; void *pad;
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; struct t3 *f;
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; } __attribute__((preserve_access_index));
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; struct t1 {
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; void *pad;
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; struct t2 *q;
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; } __attribute__((preserve_access_index));
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;
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; int g;
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; int test(struct t1 *p) {
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; struct t2 *q = p->q;
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; if (q)
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; return 0;
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; struct t3 *f = q->f;
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; if (!f) g = 5;
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; return 0;
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; }
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; Compilation flag:
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; clang -target bpf -O2 -g -S -emit-llvm t.c
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@g = dso_local local_unnamed_addr global i32 0, align 4, !dbg !0
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@"llvm.t2:0:8$0:1" = external global i64, !llvm.preserve.access.index !6 #0
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@"llvm.t1:0:8$0:1" = external global i64, !llvm.preserve.access.index !15 #0
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; Function Attrs: mustprogress nofree nosync nounwind willreturn
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define dso_local i32 @test(ptr noundef readonly %p) local_unnamed_addr #1 !dbg !25 {
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entry:
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call void @llvm.dbg.value(metadata ptr %p, metadata !30, metadata !DIExpression()), !dbg !33
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%0 = load i64, ptr @"llvm.t1:0:8$0:1", align 8
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%1 = getelementptr i8, ptr %p, i64 %0
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%2 = tail call ptr @llvm.bpf.passthrough.p0.p0(i32 1, ptr %1)
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%3 = load ptr, ptr %2, align 8, !dbg !34, !tbaa !35
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call void @llvm.dbg.value(metadata ptr %3, metadata !31, metadata !DIExpression()), !dbg !33
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%tobool.not = icmp eq ptr %3, null, !dbg !40
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br i1 %tobool.not, label %if.end, label %cleanup, !dbg !42
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; CHECK-LABEL: test
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; CHECK: r1 = *(u64 *)(r1 + 8)
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; CHECK: if r1 != 0 goto
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if.end: ; preds = %entry
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%4 = load i64, ptr @"llvm.t2:0:8$0:1", align 8
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%5 = getelementptr i8, ptr null, i64 %4
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%6 = tail call ptr @llvm.bpf.passthrough.p0.p0(i32 0, ptr %5)
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%7 = load ptr, ptr %6, align 8, !dbg !43, !tbaa !44
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call void @llvm.dbg.value(metadata ptr %7, metadata !32, metadata !DIExpression()), !dbg !33
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%tobool1.not = icmp eq ptr %7, null, !dbg !46
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br i1 %tobool1.not, label %if.then2, label %cleanup, !dbg !48
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; CHECK: r1 = 8
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; CHECK: r1 = *(u64 *)(r1 + 0)
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; CHECK: if r1 != 0 goto
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if.then2: ; preds = %if.end
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store i32 5, ptr @g, align 4, !dbg !49, !tbaa !50
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br label %cleanup, !dbg !52
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cleanup: ; preds = %if.end, %if.then2, %entry
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ret i32 0, !dbg !53
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}
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; Function Attrs: nofree nosync nounwind readnone
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declare ptr @llvm.bpf.passthrough.p0.p0(i32, ptr) #2
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; Function Attrs: nocallback nofree nosync nounwind readnone speculatable willreturn
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declare void @llvm.dbg.value(metadata, metadata, metadata) #3
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attributes #0 = { "btf_ama" }
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attributes #1 = { mustprogress nofree nosync nounwind willreturn "frame-pointer"="all" "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" }
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attributes #2 = { nofree nosync nounwind readnone }
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attributes #3 = { nocallback nofree nosync nounwind readnone speculatable willreturn }
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!llvm.dbg.cu = !{!2}
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!llvm.module.flags = !{!20, !21, !22, !23}
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!llvm.ident = !{!24}
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!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
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!1 = distinct !DIGlobalVariable(name: "g", scope: !2, file: !3, line: 13, type: !5, isLocal: false, isDefinition: true)
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!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 15.0.0 (https://github.com/llvm/llvm-project.git ca2be81e34a6d87edb8e555dfac94ab68ee20f70)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, globals: !4, splitDebugInlining: false, nameTableKind: None)
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!3 = !DIFile(filename: "t.c", directory: "/tmp/home/yhs/work/tests/llvm/nullptr", checksumkind: CSK_MD5, checksum: "2c0ea9b3c647baf31f56992f9142b0df")
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!4 = !{!0}
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!5 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
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!6 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "t2", file: !3, line: 4, size: 128, elements: !7)
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!7 = !{!8, !10}
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!8 = !DIDerivedType(tag: DW_TAG_member, name: "pad", scope: !6, file: !3, line: 5, baseType: !9, size: 64)
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!9 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null, size: 64)
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!10 = !DIDerivedType(tag: DW_TAG_member, name: "f", scope: !6, file: !3, line: 6, baseType: !11, size: 64, offset: 64)
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!11 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !12, size: 64)
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!12 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "t3", file: !3, line: 1, size: 32, elements: !13)
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!13 = !{!14}
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!14 = !DIDerivedType(tag: DW_TAG_member, name: "i", scope: !12, file: !3, line: 2, baseType: !5, size: 32)
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!15 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "t1", file: !3, line: 8, size: 128, elements: !16)
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!16 = !{!17, !18}
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!17 = !DIDerivedType(tag: DW_TAG_member, name: "pad", scope: !15, file: !3, line: 9, baseType: !9, size: 64)
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!18 = !DIDerivedType(tag: DW_TAG_member, name: "q", scope: !15, file: !3, line: 10, baseType: !19, size: 64, offset: 64)
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!19 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !6, size: 64)
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!20 = !{i32 7, !"Dwarf Version", i32 5}
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!21 = !{i32 2, !"Debug Info Version", i32 3}
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!22 = !{i32 1, !"wchar_size", i32 4}
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!23 = !{i32 7, !"frame-pointer", i32 2}
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!24 = !{!"clang version 15.0.0 (https://github.com/llvm/llvm-project.git ca2be81e34a6d87edb8e555dfac94ab68ee20f70)"}
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!25 = distinct !DISubprogram(name: "test", scope: !3, file: !3, line: 14, type: !26, scopeLine: 14, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !29)
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!26 = !DISubroutineType(types: !27)
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!27 = !{!5, !28}
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!28 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !15, size: 64)
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!29 = !{!30, !31, !32}
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!30 = !DILocalVariable(name: "p", arg: 1, scope: !25, file: !3, line: 14, type: !28)
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!31 = !DILocalVariable(name: "q", scope: !25, file: !3, line: 15, type: !19)
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!32 = !DILocalVariable(name: "f", scope: !25, file: !3, line: 18, type: !11)
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!33 = !DILocation(line: 0, scope: !25)
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!34 = !DILocation(line: 15, column: 21, scope: !25)
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!35 = !{!36, !37, i64 8}
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!36 = !{!"t1", !37, i64 0, !37, i64 8}
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!37 = !{!"any pointer", !38, i64 0}
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!38 = !{!"omnipotent char", !39, i64 0}
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!39 = !{!"Simple C/C++ TBAA"}
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!40 = !DILocation(line: 16, column: 7, scope: !41)
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!41 = distinct !DILexicalBlock(scope: !25, file: !3, line: 16, column: 7)
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!42 = !DILocation(line: 16, column: 7, scope: !25)
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!43 = !DILocation(line: 18, column: 21, scope: !25)
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!44 = !{!45, !37, i64 8}
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!45 = !{!"t2", !37, i64 0, !37, i64 8}
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!46 = !DILocation(line: 19, column: 8, scope: !47)
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!47 = distinct !DILexicalBlock(scope: !25, file: !3, line: 19, column: 7)
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!48 = !DILocation(line: 19, column: 7, scope: !25)
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!49 = !DILocation(line: 19, column: 13, scope: !47)
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!50 = !{!51, !51, i64 0}
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!51 = !{!"int", !38, i64 0}
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!52 = !DILocation(line: 19, column: 11, scope: !47)
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!53 = !DILocation(line: 21, column: 1, scope: !25)
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