[PATCH] D82881: [DEBUGINFO]Fix debug info for packed bitfields.

[Alexey Bataev via Phabricator via llvm-commits]

ABataev created this revision.
ABataev added reviewers: aprantl, probinson.
Herald added a subscriber: hiraditya.
Herald added a project: LLVM.

For the packed bitfields, the compiler emits not quite correct debug
info. Packed bitfield may use more bytes than the base type of the
bitfield. In this case, DW_AT_byte_size and DW_AT_bit_offset attributes
may have incorrect values.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D82881

Files:
  llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
  llvm/test/DebugInfo/X86/packed_bitfields.ll


Index: llvm/test/DebugInfo/X86/packed_bitfields.ll
===================================================================
--- llvm/test/DebugInfo/X86/packed_bitfields.ll
+++ llvm/test/DebugInfo/X86/packed_bitfields.ll
@@ -13,9 +13,9 @@
 ; CHECK: DW_TAG_member
 ; CHECK-NEXT: DW_AT_name{{.*}}"a"
 ; CHECK-NOT: DW_TAG_member
-; CHECK:      DW_AT_byte_size  {{.*}} (0x01)
+; CHECK:      DW_AT_byte_size  {{.*}} (0x02)
 ; CHECK-NEXT: DW_AT_bit_size   {{.*}} (0x06)
-; CHECK-NEXT: DW_AT_bit_offset {{.*}} (0xffffffffffffffff)
+; CHECK-NEXT: DW_AT_bit_offset {{.*}} (0x07)
 ; CHECK-NEXT: DW_AT_data_member_location {{.*}} (DW_OP_plus_uconst 0x0)
 
 ; ModuleID = 'repro.c'
Index: llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
===================================================================
--- llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
+++ llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
@@ -1541,12 +1541,15 @@
 
     bool IsBitfield = FieldSize && Size != FieldSize;
     if (IsBitfield) {
+      uint64_t Offset = DT->getOffsetInBits();
       // Handle bitfield, assume bytes are 8 bits.
+      uint64_t StorageSize = ((Offset + Size + 7) / 8 - Offset / 8) * 8;
+      if (StorageSize > FieldSize)
+        FieldSize = StorageSize;
       if (DD->useDWARF2Bitfields())
         addUInt(MemberDie, dwarf::DW_AT_byte_size, None, FieldSize/8);
       addUInt(MemberDie, dwarf::DW_AT_bit_size, None, Size);
 
-      uint64_t Offset = DT->getOffsetInBits();
       // We can't use DT->getAlignInBits() here: AlignInBits for member type
       // is non-zero if and only if alignment was forced (e.g. _Alignas()),
       // which can't be done with bitfields. Thus we use FieldSize here.


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