Non constant size and offset in DWARF (#141106)

In Ada, a record type can have a non-constant size, and a field can
appear at a non-constant bit offset in a record.

To support this, this patch changes DIType to record the size and offset
using metadata, rather than plain integers. In addition to a constant
offset, both DIVariable and DIExpression are now supported here.

One thing of note in this patch is the choice of how exactly to
represent a non-constant bit offset, with the difficulty being that
DWARF 5 does not support this. DWARF 3 did have a way to support a
non-constant byte offset, combined with a constant bit offset within the
byte, but this was deprecated in DWARF 4 and removed from DWARF 5.

This patch takes a simple approach: a DWARF extension allowing the use
of an expression with DW_AT_data_bit_offset. There is a corresponding
DWARF issue, see https://dwarfstd.org/issues/250501.1.html. The main
reason for this approach is that it keeps API simplicity: just a single
value is needed, rather than having separate data describing the byte
offset and the bit within the byte.

1 files changed, 21 insertions, 14 deletions

diff --git a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
index 628b939..2a2dd08 100644
--- a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -1899,10 +1899,11 @@ void ModuleBitcodeWriter::writeDIEnumerator(const DIEnumerator *N,
 void ModuleBitcodeWriter::writeDIBasicType(const DIBasicType *N,
                                            SmallVectorImpl<uint64_t> &Record,
                                            unsigned Abbrev) {
-  Record.push_back(N->isDistinct());
+  const unsigned SizeIsMetadata = 0x2;
+  Record.push_back(SizeIsMetadata | (unsigned)N->isDistinct());
   Record.push_back(N->getTag());
   Record.push_back(VE.getMetadataOrNullID(N->getRawName()));
-  Record.push_back(N->getSizeInBits());
+  Record.push_back(VE.getMetadataOrNullID(N->getRawSizeInBits()));
   Record.push_back(N->getAlignInBits());
   Record.push_back(N->getEncoding());
   Record.push_back(N->getFlags());
@@ -1915,10 +1916,11 @@ void ModuleBitcodeWriter::writeDIBasicType(const DIBasicType *N,
 void ModuleBitcodeWriter::writeDIFixedPointType(
     const DIFixedPointType *N, SmallVectorImpl<uint64_t> &Record,
     unsigned Abbrev) {
-  Record.push_back(N->isDistinct());
+  const unsigned SizeIsMetadata = 0x2;
+  Record.push_back(SizeIsMetadata | (unsigned)N->isDistinct());
   Record.push_back(N->getTag());
   Record.push_back(VE.getMetadataOrNullID(N->getRawName()));
-  Record.push_back(N->getSizeInBits());
+  Record.push_back(VE.getMetadataOrNullID(N->getRawSizeInBits()));
   Record.push_back(N->getAlignInBits());
   Record.push_back(N->getEncoding());
   Record.push_back(N->getFlags());
@@ -1944,13 +1946,14 @@ void ModuleBitcodeWriter::writeDIFixedPointType(
 void ModuleBitcodeWriter::writeDIStringType(const DIStringType *N,
                                             SmallVectorImpl<uint64_t> &Record,
                                             unsigned Abbrev) {
-  Record.push_back(N->isDistinct());
+  const unsigned SizeIsMetadata = 0x2;
+  Record.push_back(SizeIsMetadata | (unsigned)N->isDistinct());
   Record.push_back(N->getTag());
   Record.push_back(VE.getMetadataOrNullID(N->getRawName()));
   Record.push_back(VE.getMetadataOrNullID(N->getStringLength()));
   Record.push_back(VE.getMetadataOrNullID(N->getStringLengthExp()));
   Record.push_back(VE.getMetadataOrNullID(N->getStringLocationExp()));
-  Record.push_back(N->getSizeInBits());
+  Record.push_back(VE.getMetadataOrNullID(N->getRawSizeInBits()));
   Record.push_back(N->getAlignInBits());
   Record.push_back(N->getEncoding());
 
@@ -1961,16 +1964,17 @@ void ModuleBitcodeWriter::writeDIStringType(const DIStringType *N,
 void ModuleBitcodeWriter::writeDIDerivedType(const DIDerivedType *N,
                                              SmallVectorImpl<uint64_t> &Record,
                                              unsigned Abbrev) {
-  Record.push_back(N->isDistinct());
+  const unsigned SizeIsMetadata = 0x2;
+  Record.push_back(SizeIsMetadata | (unsigned)N->isDistinct());
   Record.push_back(N->getTag());
   Record.push_back(VE.getMetadataOrNullID(N->getRawName()));
   Record.push_back(VE.getMetadataOrNullID(N->getFile()));
   Record.push_back(N->getLine());
   Record.push_back(VE.getMetadataOrNullID(N->getScope()));
   Record.push_back(VE.getMetadataOrNullID(N->getBaseType()));
-  Record.push_back(N->getSizeInBits());
+  Record.push_back(VE.getMetadataOrNullID(N->getRawSizeInBits()));
   Record.push_back(N->getAlignInBits());
-  Record.push_back(N->getOffsetInBits());
+  Record.push_back(VE.getMetadataOrNullID(N->getRawOffsetInBits()));
   Record.push_back(N->getFlags());
   Record.push_back(VE.getMetadataOrNullID(N->getExtraData()));
 
@@ -1995,12 +1999,13 @@ void ModuleBitcodeWriter::writeDIDerivedType(const DIDerivedType *N,
 void ModuleBitcodeWriter::writeDISubrangeType(const DISubrangeType *N,
                                               SmallVectorImpl<uint64_t> &Record,
                                               unsigned Abbrev) {
-  Record.push_back(N->isDistinct());
+  const unsigned SizeIsMetadata = 0x2;
+  Record.push_back(SizeIsMetadata | (unsigned)N->isDistinct());
   Record.push_back(VE.getMetadataOrNullID(N->getRawName()));
   Record.push_back(VE.getMetadataOrNullID(N->getFile()));
   Record.push_back(N->getLine());
   Record.push_back(VE.getMetadataOrNullID(N->getScope()));
-  Record.push_back(N->getSizeInBits());
+  Record.push_back(VE.getMetadataOrNullID(N->getRawSizeInBits()));
   Record.push_back(N->getAlignInBits());
   Record.push_back(N->getFlags());
   Record.push_back(VE.getMetadataOrNullID(N->getBaseType()));
@@ -2017,16 +2022,18 @@ void ModuleBitcodeWriter::writeDICompositeType(
     const DICompositeType *N, SmallVectorImpl<uint64_t> &Record,
     unsigned Abbrev) {
   const unsigned IsNotUsedInOldTypeRef = 0x2;
-  Record.push_back(IsNotUsedInOldTypeRef | (unsigned)N->isDistinct());
+  const unsigned SizeIsMetadata = 0x4;
+  Record.push_back(SizeIsMetadata | IsNotUsedInOldTypeRef |
+                   (unsigned)N->isDistinct());
   Record.push_back(N->getTag());
   Record.push_back(VE.getMetadataOrNullID(N->getRawName()));
   Record.push_back(VE.getMetadataOrNullID(N->getFile()));
   Record.push_back(N->getLine());
   Record.push_back(VE.getMetadataOrNullID(N->getScope()));
   Record.push_back(VE.getMetadataOrNullID(N->getBaseType()));
-  Record.push_back(N->getSizeInBits());
+  Record.push_back(VE.getMetadataOrNullID(N->getRawSizeInBits()));
   Record.push_back(N->getAlignInBits());
-  Record.push_back(N->getOffsetInBits());
+  Record.push_back(VE.getMetadataOrNullID(N->getRawOffsetInBits()));
   Record.push_back(N->getFlags());
   Record.push_back(VE.getMetadataOrNullID(N->getElements().get()));
   Record.push_back(N->getRuntimeLang());