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1650f1b3d7f97ca95eb930984e74bdfd91b02b4e
clang-p2996/llvm/test/CodeGen/BPF/CORE/simplify-patchable-liveness-bug.ll
Eduard Zingerman 27026fe563 [BPF] Reset machine register kill mark in BPFMISimplifyPatchable 
When LLVM is build with `LLVM_ENABLE_EXPENSIVE_CHECKS=ON` option
the following C code snippet:

    struct t {
      unsigned long a;
    } __attribute__((preserve_access_index));

    void foo(volatile struct t *t, volatile unsigned long *p) {
      *p = t->a;
      *p = t->a;
    }

Causes an assertion:

    $ clang -g -O2 -c --target=bpf -mcpu=v2 t2.c -o /dev/null

    # After BPF PreEmit SimplifyPatchable
    # Machine code for function foo: IsSSA, TracksLiveness
    Function Live Ins: $r1 in %0, $r2 in %1

    bb.0.entry:
      liveins: $r1, $r2
      DBG_VALUE $r1, $noreg, !"t", !DIExpression()
      DBG_VALUE $r2, $noreg, !"p", !DIExpression()
      %1:gpr = COPY $r2
      DBG_VALUE %1:gpr, $noreg, !"p", !DIExpression()
      %0:gpr = COPY $r1
      DBG_VALUE %0:gpr, $noreg, !"t", !DIExpression()
      %2:gpr = LD_imm64 @"llvm.t:0:0$0:0"
      %4:gpr = ADD_rr %0:gpr(tied-def 0), killed %2:gpr
      %5:gpr = CORE_LD 344, %0:gpr, @"llvm.t:0:0$0:0"
      STD killed %5:gpr, %1:gpr, 0
      %7:gpr = ADD_rr %0:gpr(tied-def 0), killed %2:gpr
      %8:gpr = CORE_LD 344, %0:gpr, @"llvm.t:0:0$0:0"
      STD killed %8:gpr, %1:gpr, 0
      RET

    # End machine code for function foo.

    *** Bad machine code: Using a killed virtual register ***
    - function:    foo
    - basic block: %bb.0 entry (0x6210000e6690)
    - instruction: %7:gpr = ADD_rr %0:gpr(tied-def 0), killed %2:gpr
    - operand 2:   killed %2:gpr

This happens because of the way
BPFMISimplifyPatchable::processDstReg() updates second operand of the
`ADD_rr` instruction. Code before `BPFMISimplifyPatchable`:

    .-> %2:gpr = LD_imm64 @"llvm.t:0:0$0:0"
    |
    |`----------------.
    |   %3:gpr = LDD %2:gpr, 0
    |   %4:gpr = ADD_rr %0:gpr(tied-def 0), killed %3:gpr <--- (1)
    |   %5:gpr = LDD killed %4:gpr, 0       ^^^^^^^^^^^^^
    |   STD killed %5:gpr, %1:gpr, 0        this is updated
     `----------------.
        %6:gpr = LDD %2:gpr, 0
        %7:gpr = ADD_rr %0:gpr(tied-def 0), killed %6:gpr <--- (2)
        %8:gpr = LDD killed %7:gpr, 0       ^^^^^^^^^^^^^
        STD killed %8:gpr, %1:gpr, 0        this is updated

Instructions (1) and (2) would be updated to:

    ADD_rr %0:gpr(tied-def 0), killed %2:gpr

The `killed` mark is inherited from machine operands `killed %3:gpr`
and `killed %6:gpr` which are updated inplace by `processDstReg()`.

This commit updates `processDstReg()` reset kill marks for updated
machine operands to keep liveness information conservatively correct.

Differential Revision: https://reviews.llvm.org/D157805
2023-08-15 02:23:38 +03:00

122 lines
5.2 KiB
LLVM
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; RUN: llc -mtriple=bpf -mcpu=v2 < %s | FileCheck -check-prefixes=CHECK %s
; Test for machine register liveness update bug in
; BPFMISimplifyPatchable::processDstReg.
;
; Generated from the following source code:
; struct t {
; unsigned long a;
; } __attribute__((preserve_access_index));
;
; void foo(volatile struct t *t, volatile unsigned long *p) {
; *p = t->a;
; *p = t->a;
; }
;
; Using the following command:
; clang -g -O2 -S -emit-llvm --target=bpf t.c -o t.ll
@"llvm.t:0:0$0:0" = external global i64, !llvm.preserve.access.index !0 #0
; Function Attrs: nofree nounwind
define dso_local void @foo(ptr noundef %t, ptr noundef %p) local_unnamed_addr #1 !dbg !12 {
entry:
call void @llvm.dbg.value(metadata ptr %t, metadata !20, metadata !DIExpression()), !dbg !22
call void @llvm.dbg.value(metadata ptr %p, metadata !21, metadata !DIExpression()), !dbg !22
%0 = load i64, ptr @"llvm.t:0:0$0:0", align 8
%1 = getelementptr i8, ptr %t, i64 %0
%2 = tail call ptr @llvm.bpf.passthrough.p0.p0(i32 0, ptr %1)
%3 = load volatile i64, ptr %2, align 8, !dbg !23, !tbaa !24
store volatile i64 %3, ptr %p, align 8, !dbg !29, !tbaa !30
%4 = load i64, ptr @"llvm.t:0:0$0:0", align 8
%5 = getelementptr i8, ptr %t, i64 %4
%6 = tail call ptr @llvm.bpf.passthrough.p0.p0(i32 1, ptr %5)
%7 = load volatile i64, ptr %6, align 8, !dbg !31, !tbaa !24
store volatile i64 %7, ptr %p, align 8, !dbg !32, !tbaa !30
ret void, !dbg !33
}
; CHECK: foo:
; CHECK: prologue_end
; CHECK-NEXT: .Ltmp[[LABEL1:.*]]:
; CHECK-NEXT: .Ltmp
; CHECK-NEXT: r[[#A:]] = *(u64 *)(r1 + 0)
; CHECK-NEXT: .loc
; CHECK-NEXT: .Ltmp
; CHECK-NEXT: *(u64 *)(r2 + 0) = r[[#A]]
; CHECK-NEXT: .loc
; CHECK-NEXT: .Ltmp[[LABEL2:.*]]:
; CHECK-NEXT: .Ltmp
; CHECK-NEXT: r[[#B:]] = *(u64 *)(r1 + 0)
; CHECK-NEXT: .Ltmp
; CHECK-NEXT: .Ltmp
; CHECK-NEXT: .loc
; CHECK-NEXT: .Ltmp
; CHECK-NEXT: *(u64 *)(r2 + 0) = r[[#B]]
; CHECK: .section .BTF
; CHECK: .long [[STR_T:.*]] # BTF_KIND_STRUCT(id = [[ID:.*]])
; CHECK: .byte 116 # string offset=[[STR_T]]
; CHECK: .ascii "0:0" # string offset=[[STR_A:.*]]
; CHECK: # FieldReloc
; CHECK: .long .Ltmp[[LABEL1]]
; CHECK-NEXT: .long [[ID]]
; CHECK-NEXT: .long [[STR_A]]
; CHECK-NEXT: .long 0
; CHECK: .long .Ltmp[[LABEL2]]
; CHECK-NEXT: .long [[ID]]
; CHECK-NEXT: .long [[STR_A]]
; CHECK-NEXT: .long 0
; Function Attrs: nofree nosync nounwind memory(none)
declare ptr @llvm.bpf.passthrough.p0.p0(i32, ptr) #2
; Function Attrs: nocallback nofree nosync nounwind speculatable willreturn memory(none)
declare void @llvm.dbg.value(metadata, metadata, metadata) #3
attributes #0 = { "btf_ama" }
attributes #1 = { nofree nounwind "frame-pointer"="all" "no-trapping-math"="true" "stack-protector-buffer-size"="8" }
attributes #2 = { nofree nosync nounwind memory(none) }
attributes #3 = { nocallback nofree nosync nounwind speculatable willreturn memory(none) }
!llvm.dbg.cu = !{!5}
!llvm.module.flags = !{!6, !7, !8, !9, !10}
!llvm.ident = !{!11}
!0 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "t", file: !1, line: 1, size: 64, elements: !2)
!1 = !DIFile(filename: "some.file", directory: "/some/dir", checksumkind: CSK_MD5, checksum: "a149cfaf65a83125e7f2b2f47e5c7287")
!2 = !{!3}
!3 = !DIDerivedType(tag: DW_TAG_member, name: "a", scope: !0, file: !1, line: 2, baseType: !4, size: 64)
!4 = !DIBasicType(name: "unsigned long", size: 64, encoding: DW_ATE_unsigned)
!5 = distinct !DICompileUnit(language: DW_LANG_C11, file: !1, producer: "clang version 18.0.0 (/home/eddy/work/llvm-project/clang 3810f2eb4382d5e2090ce5cd47f45379cb453c35)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
!6 = !{i32 7, !"Dwarf Version", i32 5}
!7 = !{i32 2, !"Debug Info Version", i32 3}
!8 = !{i32 1, !"wchar_size", i32 4}
!9 = !{i32 7, !"frame-pointer", i32 2}
!10 = !{i32 7, !"debug-info-assignment-tracking", i1 true}
!11 = !{!"clang version 18.0.0 (/home/eddy/work/llvm-project/clang 3810f2eb4382d5e2090ce5cd47f45379cb453c35)"}
!12 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 4, type: !13, scopeLine: 4, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !5, retainedNodes: !19)
!13 = !DISubroutineType(types: !14)
!14 = !{null, !15, !17}
!15 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !16, size: 64)
!16 = !DIDerivedType(tag: DW_TAG_volatile_type, baseType: !0)
!17 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !18, size: 64)
!18 = !DIDerivedType(tag: DW_TAG_volatile_type, baseType: !4)
!19 = !{!20, !21}
!20 = !DILocalVariable(name: "t", arg: 1, scope: !12, file: !1, line: 4, type: !15)
!21 = !DILocalVariable(name: "p", arg: 2, scope: !12, file: !1, line: 4, type: !17)
!22 = !DILocation(line: 0, scope: !12)
!23 = !DILocation(line: 5, column: 11, scope: !12)
!24 = !{!25, !26, i64 0}
!25 = !{!"t", !26, i64 0}
!26 = !{!"long", !27, i64 0}
!27 = !{!"omnipotent char", !28, i64 0}
!28 = !{!"Simple C/C++ TBAA"}
!29 = !DILocation(line: 5, column: 6, scope: !12)
!30 = !{!26, !26, i64 0}
!31 = !DILocation(line: 6, column: 11, scope: !12)
!32 = !DILocation(line: 6, column: 6, scope: !12)
!33 = !DILocation(line: 7, column: 1, scope: !12)
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