[DWARF][DebugInfo] Fix off-by-one error in size of DW_TAG_base_type types

[Orlando]

Summary

Fix PR53163 by rounding the byte size of DW_TAG_base_type types up. Without
this fix we risk emitting types with a truncated size (including rounding
less-than-byte-sized types' sizes down to zero).

[probinson]

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

1585

You'd think there would be a convenience macro for this, but I'm not finding one. I do have a memory that someone started making some changes to remove the hard-coded assumption about 8-bit bytes, but it's vague and unless someone else can come up with an example of doing this differently, it's not a blocker.

llvm/test/DebugInfo/X86/base-type-size.ll

15

Needs CHECK-NEXT to ensure the name/encoding/byte_size all belong to the same DIE.
(If this isn't the first base_type, that may be slightly tricky...)

[Orlando]

Thanks for taking a look @probinson.

+ Use CHECK-NEXT directives in test
+ Use divideCeil instead of inline maths

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

1585

I had vague memories about hardcoded 8-bit bytes too. Since you mentioned it, I had a look around in DataLayout but I couldn't find anything that would give me the size of a byte and many of the Datalayout methods appear to assume it's 8 bits. In my rummaging around I did find divideCeil at least, which makes this slightly tidier.

[Orlando]

+ Fix comment in test: -g -> -gdwarf-5

[probinson]

LGTM

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

void DwarfCompileUnit::createBaseTypeDIEs() {
   for (auto &Btr : reverse(ExprRefedBaseTypes)) {
     DIE &Die = getUnitDie().addChildFront(
       DIE::get(DIEValueAllocator, dwarf::DW_TAG_base_type));
     SmallString<32> Str;
     addString(Die, dwarf::DW_AT_name,
               Twine(dwarf::AttributeEncodingString(Btr.Encoding) +
                     "_" + Twine(Btr.BitSize)).toStringRef(Str));
     addUInt(Die, dwarf::DW_AT_encoding, dwarf::DW_FORM_data1, Btr.Encoding);
-    addUInt(Die, dwarf::DW_AT_byte_size, None, Btr.BitSize / 8);
+    // Round up to smallest number of bytes that contains this number of bits.
+    addUInt(Die, dwarf::DW_AT_byte_size, None, divideCeil(Btr.BitSize, 8));
 
     Btr.Die = &Die;
   }
 }

llvm/test/DebugInfo/X86/base-type-size.ll

+; RUN: llc %s --filetype=obj -o - | llvm-dwarfdump - -o - | FileCheck %s
+
+;; cat test.cpp
+;; void ext(bool);
+;; void fun(bool b) { ext(b); }
+;; $ clang++ test.cpp -o - -emit-llvm -S -O2 -gdwarf-5
+;;
+;; Check that the DW_TAG_base_type DIE for the 1u conversion in the DIExpression
+;; has a non-zero DW_AT_byte_size attribute.
+
+; CHECK: DW_TAG_base_type
+; CHECK-NEXT: DW_AT_name      ("DW_ATE_unsigned_1")
+; CHECK-NEXT: DW_AT_encoding  (DW_ATE_unsigned)
+; CHECK-NEXT: DW_AT_byte_size (0x01)
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define dso_local void @_Z3funb(i1 zeroext %b) local_unnamed_addr #0 !dbg !7 {
+entry:
+  call void @llvm.dbg.value(metadata i1 %b, metadata !12, metadata !DIExpression(DW_OP_LLVM_convert, 1, DW_ATE_unsigned, DW_OP_LLVM_convert, 8, DW_ATE_unsigned, DW_OP_stack_value)), !dbg !13
+  tail call void @_Z3extb(i1 zeroext %b), !dbg !14
+  ret void, !dbg !15
+}
+
+declare !dbg !16 dso_local void @_Z3extb(i1 zeroext) local_unnamed_addr
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 14.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "test.cpp", directory: "/")
+!2 = !{i32 7, !"Dwarf Version", i32 5}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !{i32 1, !"wchar_size", i32 4}
+!5 = !{i32 7, !"uwtable", i32 1}
+!6 = !{!"clang version 14.0.0"}
+!7 = distinct !DISubprogram(name: "fun", linkageName: "_Z3funb", scope: !1, file: !1, line: 2, type: !8, scopeLine: 2, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !11)
+!8 = !DISubroutineType(types: !9)
+!9 = !{null, !10}
+!10 = !DIBasicType(name: "bool", size: 8, encoding: DW_ATE_boolean)
+!11 = !{!12}
+!12 = !DILocalVariable(name: "b", arg: 1, scope: !7, file: !1, line: 2, type: !10)
+!13 = !DILocation(line: 0, scope: !7)
+!14 = !DILocation(line: 2, column: 20, scope: !7)
+!15 = !DILocation(line: 2, column: 28, scope: !7)
+!16 = !DISubprogram(name: "ext", linkageName: "_Z3extb", scope: !1, file: !1, line: 1, type: !8, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !17)
+!17 = !{}