[BPF] Fix a bug for __builtin_preserve_field_info() processing

Andrii discovered a problem where a simple case similar to below
will generate wrong relocation kind:
  enum { FIELD_EXISTENCE = 2, };
  struct s1 { int a1; };
  int test() {
    struct s1 *v = 0;
    return __builtin_preserve_field_info(v[0], FIELD_EXISTENCE);
  }
The expected relocation kind should be FIELD_EXISTENCE, but
recorded reloc kind in the final object file is FIELD_BYTE_OFFSET,
which is incorrect.

This exposed a bug in generating access strings from intrinsics.
The current access string generation has two steps:
  step 1: find the base struct/union type,
  step 2: traverse members in the base type.

The current implementation relies on at lease one member access
in step 2 to get the correct relocation kind, which is true
in typical cases. But if there is no member accesses, the current
implementation falls to the default info kind FIELD_BYTE_OFFSET.
This is incorrect, we should still record the reloc kind
based on the user input. This patch fixed this issue by properly
recording the reloc kind in such cases.

Differential Revision: https://reviews.llvm.org/D82932

diff --git a/llvm/lib/Target/BPF/BPFAbstractMemberAccess.cpp b/llvm/lib/Target/BPF/BPFAbstractMemberAccess.cpp
index b213b15..5b42d91 100644 (file)
--- a/llvm/lib/Target/BPF/BPFAbstractMemberAccess.cpp
+++ b/llvm/lib/Target/BPF/BPFAbstractMemberAccess.cpp
@@ -808,8 +808,10 @@ Value *BPFAbstractMemberAccess::computeBaseAndAccessKey(CallInst *Call,
     CInfo = StackElem.second;
     CallStack.pop();
 
-    if (CInfo.Kind == BPFPreserveFieldInfoAI)
+    if (CInfo.Kind == BPFPreserveFieldInfoAI) {
+      InfoKind = CInfo.AccessIndex;
       break;
+    }
 
     // If the next Call (the top of the stack) is a BPFPreserveFieldInfoAI,
     // the action will be extracting field info.

diff --git a/llvm/test/CodeGen/BPF/CORE/intrinsic-array-2.ll b/llvm/test/CodeGen/BPF/CORE/intrinsic-array-2.ll
new file mode 100644 (file)
index 0000000..8c8ee09
--- /dev/null
+++ b/llvm/test/CodeGen/BPF/CORE/intrinsic-array-2.ll
@@ -0,0 +1,82 @@
+; RUN: llc -march=bpfel -filetype=asm -o - %s | FileCheck -check-prefixes=CHECK,CHECK-ALU64 %s
+; RUN: llc -march=bpfeb -filetype=asm -o - %s | FileCheck -check-prefixes=CHECK,CHECK-ALU64 %s
+; RUN: llc -march=bpfel -mattr=+alu32 -filetype=asm -o - %s | FileCheck -check-prefixes=CHECK,CHECK-ALU32 %s
+; RUN: llc -march=bpfeb -mattr=+alu32 -filetype=asm -o - %s | FileCheck -check-prefixes=CHECK,CHECK-ALU32 %s
+; Source:
+;   enum { FIELD_EXISTENCE = 2, };
+;   struct s1 { int a1; };
+;   int test() {
+;     struct s1 *v = 0;
+;     return __builtin_preserve_field_info(v[0], FIELD_EXISTENCE);
+;   }
+; Compilation flag:
+;   clang -target bpf -O2 -g -S -emit-llvm test.c
+
+%struct.s1 = type { i32 }
+
+; Function Attrs: nounwind readnone
+define dso_local i32 @test() local_unnamed_addr #0 !dbg !17 {
+entry:
+  call void @llvm.dbg.value(metadata %struct.s1* null, metadata !21, metadata !DIExpression()), !dbg !22
+  %0 = tail call %struct.s1* @llvm.preserve.array.access.index.p0s_struct.s1s.p0s_struct.s1s(%struct.s1* null, i32 0, i32 0), !dbg !23, !llvm.preserve.access.index !8
+  %1 = tail call i32 @llvm.bpf.preserve.field.info.p0s_struct.s1s(%struct.s1* %0, i64 2), !dbg !24
+  ret i32 %1, !dbg !25
+}
+
+; CHECK:             .long   16                      # BTF_KIND_STRUCT(id = 4)
+
+; CHECK:             .ascii  ".text"                 # string offset=10
+; CHECK:             .ascii  "s1"                    # string offset=16
+; CHECK:             .byte   48                      # string offset=22
+
+; CHECK:             .long   16                      # FieldReloc
+; CHECK-NEXT:        .long   10                      # Field reloc section string offset=10
+; CHECK-NEXT:        .long   1
+; CHECK-NEXT:        .long   .Ltmp{{[0-9]+}}
+; CHECK-NEXT:        .long   4
+; CHECK-NEXT:        .long   22
+; CHECK-NEXT:        .long   2
+
+; Function Attrs: nounwind readnone
+declare %struct.s1* @llvm.preserve.array.access.index.p0s_struct.s1s.p0s_struct.s1s(%struct.s1*, i32 immarg, i32 immarg) #1
+
+; Function Attrs: nounwind readnone
+declare i32 @llvm.bpf.preserve.field.info.p0s_struct.s1s(%struct.s1*, i64 immarg) #1
+
+; Function Attrs: nounwind readnone speculatable willreturn
+declare void @llvm.dbg.value(metadata, metadata, metadata) #2
+
+attributes #0 = { nounwind readnone "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"="true" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { nounwind readnone }
+attributes #2 = { nounwind readnone speculatable willreturn }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!13, !14, !15}
+!llvm.ident = !{!16}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 11.0.0 (https://github.com/llvm/llvm-project.git 32791937d7aceb0a5e1eaabf1bb1a6dbe1639792)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !7, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "test.c", directory: "/tmp/home/yhs/work/tests/core")
+!2 = !{!3}
+!3 = !DICompositeType(tag: DW_TAG_enumeration_type, file: !1, line: 1, baseType: !4, size: 32, elements: !5)
+!4 = !DIBasicType(name: "unsigned int", size: 32, encoding: DW_ATE_unsigned)
+!5 = !{!6}
+!6 = !DIEnumerator(name: "FIELD_EXISTENCE", value: 2, isUnsigned: true)
+!7 = !{!8}
+!8 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !9, size: 64)
+!9 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "s1", file: !1, line: 2, size: 32, elements: !10)
+!10 = !{!11}
+!11 = !DIDerivedType(tag: DW_TAG_member, name: "a1", scope: !9, file: !1, line: 2, baseType: !12, size: 32)
+!12 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!13 = !{i32 7, !"Dwarf Version", i32 4}
+!14 = !{i32 2, !"Debug Info Version", i32 3}
+!15 = !{i32 1, !"wchar_size", i32 4}
+!16 = !{!"clang version 11.0.0 (https://github.com/llvm/llvm-project.git 32791937d7aceb0a5e1eaabf1bb1a6dbe1639792)"}
+!17 = distinct !DISubprogram(name: "test", scope: !1, file: !1, line: 3, type: !18, scopeLine: 3, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !20)
+!18 = !DISubroutineType(types: !19)
+!19 = !{!12}
+!20 = !{!21}
+!21 = !DILocalVariable(name: "v", scope: !17, file: !1, line: 4, type: !8)
+!22 = !DILocation(line: 0, scope: !17)
+!23 = !DILocation(line: 5, column: 40, scope: !17)
+!24 = !DILocation(line: 5, column: 10, scope: !17)
+!25 = !DILocation(line: 5, column: 3, scope: !17)