[BPF] fix a bug in __builtin_preserve_field_info() with FIELD_BYTE_SIZE

[yonghong-song]

Summary

During deriving proper bitfield access FIELD_BYTE_SIZE,
function Member->getStorageOffsetInBits() is used to
get llvm IR type storage offset in bits so that
the byte size can permit aligned loads/stores with previously
derived FIELD_BYTE_OFFSET.

The function should only be used with bitfield members and it will
assert if ASSERT is turned on during cmake build.

Constant *getStorageOffsetInBits() const {
  assert(getTag() == dwarf::DW_TAG_member && isBitField());
  if (auto *C = cast_or_null<ConstantAsMetadata>(getExtraData()))
    return C->getValue();
  return nullptr;
}

This patch fixed the issue by using Member->isBitField()
directly and a test case is added to cover this missing case.
This issue is discovered when running Andrii's linux kernel CO-RE
tests.

llvm/lib/Target/BPF/BPFAbstractMemberAccess.cpp

void BPFAbstractMemberAccess::GetStorageBitRange(DICompositeType *CTy,
   auto SOff = dyn_cast<ConstantInt>(MemberTy->getStorageOffsetInBits());
   assert(SOff);
   StartBitOffset = SOff->getZExtValue();
 
   EndBitOffset = CTy->getSizeInBits();
   uint32_t Index = AccessIndex + 1;
   for (; Index < CTy->getElements().size(); ++Index) {
     auto Member = cast<DIDerivedType>(CTy->getElements()[Index]);
-    if (!Member->getStorageOffsetInBits()) {
+    if (!Member->isBitField()) {
       EndBitOffset = Member->getOffsetInBits();
       break;
     }
     SOff = dyn_cast<ConstantInt>(Member->getStorageOffsetInBits());
     assert(SOff);
     unsigned BitOffset = SOff->getZExtValue();
     if (BitOffset != StartBitOffset) {
       EndBitOffset = BitOffset;

llvm/test/CodeGen/BPF/CORE/intrinsic-fieldinfo-byte-size-4.ll

+; 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
+; RUN: llc -march=bpfel -mattr=+alu32 -filetype=asm -o - %s | FileCheck -check-prefixes=CHECK %s
+; RUN: llc -march=bpfeb -mattr=+alu32 -filetype=asm -o - %s | FileCheck -check-prefixes=CHECK %s
+; Source code:
+;   typedef struct s1 { int a1; int a2:4; int a3;} __s1;
+;   enum { FIELD_BYTE_SIZE = 1, };
+;   int test(__s1 *arg) {
+;     return __builtin_preserve_field_info(arg->a2, FIELD_BYTE_SIZE);
+;   }
+; Compilation flag:
+;   clang -target bpf -O2 -g -S -emit-llvm test.c
+
+%struct.s1 = type { i32, i8, i32 }
+
+; Function Attrs: nounwind readnone
+define dso_local i32 @test(%struct.s1* readnone %arg) local_unnamed_addr #0 !dbg !11 {
+entry:
+  call void @llvm.dbg.value(metadata %struct.s1* %arg, metadata !23, metadata !DIExpression()), !dbg !24
+  %0 = tail call i8* @llvm.preserve.struct.access.index.p0i8.p0s_struct.s1s(%struct.s1* %arg, i32 1, i32 1), !dbg !25, !llvm.preserve.access.index !17
+  %1 = tail call i32 @llvm.bpf.preserve.field.info.p0i8(i8* %0, i64 1), !dbg !26
+  ret i32 %1, !dbg !27
+}
+
+; CHECK:             r0 = 4
+; CHECK:             exit
+
+; CHECK:             .long   6                       # BTF_KIND_STRUCT(id = 3)
+
+; CHECK:             .ascii  "s1"                    # string offset=6
+; CHECK:             .ascii  ".text"                 # string offset=31
+; CHECK:             .ascii  "0:1"                   # string offset=37
+
+; CHECK:             .long   16                      # FieldReloc
+; CHECK-NEXT:        .long   31                      # Field reloc section string offset=31
+; CHECK-NEXT:        .long   1
+; CHECK-NEXT:        .long   .Ltmp{{[0-9]+}}
+; CHECK-NEXT:        .long   3
+; CHECK-NEXT:        .long   37
+; CHECK-NEXT:        .long   1
+
+; Function Attrs: nounwind readnone
+declare i8* @llvm.preserve.struct.access.index.p0i8.p0s_struct.s1s(%struct.s1*, i32, i32) #1
+
+; Function Attrs: nounwind readnone
+declare i32 @llvm.bpf.preserve.field.info.p0i8(i8*, i64) #1
+
+; Function Attrs: nounwind readnone speculatable
+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"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { nounwind readnone }
+attributes #2 = { nounwind readnone speculatable }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!7, !8, !9}
+!llvm.ident = !{!10}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 10.0.0 (https://github.com/llvm/llvm-project.git 6c63b5d6a1cb84a75807804337c855a41c976260)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, 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: 2, baseType: !4, size: 32, elements: !5)
+!4 = !DIBasicType(name: "unsigned int", size: 32, encoding: DW_ATE_unsigned)
+!5 = !{!6}
+!6 = !DIEnumerator(name: "FIELD_BYTE_SIZE", value: 1, isUnsigned: true)
+!7 = !{i32 2, !"Dwarf Version", i32 4}
+!8 = !{i32 2, !"Debug Info Version", i32 3}
+!9 = !{i32 1, !"wchar_size", i32 4}
+!10 = !{!"clang version 10.0.0 (https://github.com/llvm/llvm-project.git 6c63b5d6a1cb84a75807804337c855a41c976260)"}
+!11 = distinct !DISubprogram(name: "test", scope: !1, file: !1, line: 3, type: !12, scopeLine: 3, flags: DIFlagPrototyped, isDefinition: true, isOptimized: true, unit: !0, retainedNodes: !22)
+!12 = !DISubroutineType(types: !13)
+!13 = !{!14, !15}
+!14 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!15 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !16, size: 64)
+!16 = !DIDerivedType(tag: DW_TAG_typedef, name: "__s1", file: !1, line: 1, baseType: !17)
+!17 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "s1", file: !1, line: 1, size: 96, elements: !18)
+!18 = !{!19, !20, !21}
+!19 = !DIDerivedType(tag: DW_TAG_member, name: "a1", scope: !17, file: !1, line: 1, baseType: !14, size: 32)
+!20 = !DIDerivedType(tag: DW_TAG_member, name: "a2", scope: !17, file: !1, line: 1, baseType: !14, size: 4, offset: 32, flags: DIFlagBitField, extraData: i64 32)
+!21 = !DIDerivedType(tag: DW_TAG_member, name: "a3", scope: !17, file: !1, line: 1, baseType: !14, size: 32, offset: 64)
+!22 = !{!23}
+!23 = !DILocalVariable(name: "arg", arg: 1, scope: !11, file: !1, line: 3, type: !15)
+!24 = !DILocation(line: 0, scope: !11)
+!25 = !DILocation(line: 4, column: 45, scope: !11)
+!26 = !DILocation(line: 4, column: 10, scope: !11)
+!27 = !DILocation(line: 4, column: 3, scope: !11)