Skip to content

Commit

Permalink
Rollup merge of #135156 - Zalathar:debuginfo-flags, r=cuviper
Browse files Browse the repository at this point in the history 
Make our `DIFlags` match `LLVMDIFlags` in the LLVM-C API

In order to be able to use a mixture of LLVM-C and C++ bindings for debuginfo, our Rust-side `DIFlags` needs to have the same layout as LLVM-C's `LLVMDIFlags`, and we also need to be able to convert it to the `DIFlags` accepted by LLVM's C++ API.

Internally, LLVM converts between the two types with a simple cast. We can't necessarily rely on that always being true, and LLVM doesn't expose a conversion function, so we have two potential options:
- Convert each bit/subvalue individually
- Statically assert that doing a cast is actually fine

As long as both types do remain the same under the hood (which seems likely), the static-assert-and-cast approach is easier and faster. If the static assertions ever start failing against some future version of LLVM, we'll have to switch over to the convert-each-subvalue approach, which is a bit more error-prone.

---

Extracted from #134009, though this PR ended up choosing the static-assert-and-cast approach over the convert-each-subvalue approach.
  • Loading branch information
@matthiaskrgr
matthiaskrgr authored Jan 22, 2025
2 parents df01040 + d10bdaf commit e0d74c0
Show file tree
Hide file tree
Showing 3 changed files with 87 additions and 117 deletions.
2 changes: 2 additions & 0 deletions compiler/rustc_codegen_llvm/Cargo.toml
View file
Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,8 @@ test = false
[dependencies]
# tidy-alphabetical-start
bitflags = "2.4.1"
# To avoid duplicate dependencies, this should match the version of gimli used
# by `rustc_codegen_ssa` via its `thorin-dwp` dependency.
gimli = "0.30"
itertools = "0.12"
libc = "0.2"
Expand Down
20 changes: 17 additions & 3 deletions compiler/rustc_codegen_llvm/src/llvm/ffi.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -741,8 +741,11 @@ pub mod debuginfo {
pub type DIEnumerator = DIDescriptor;
pub type DITemplateTypeParameter = DIDescriptor;

// These values **must** match with LLVMRustDIFlags!!
bitflags! {
/// Must match the layout of `LLVMDIFlags` in the LLVM-C API.
///
/// Each value declared here must also be covered by the static
/// assertions in `RustWrapper.cpp` used by `fromRust(LLVMDIFlags)`.
#[repr(transparent)]
#[derive(Clone, Copy, Default)]
pub struct DIFlags: u32 {
Expand All @@ -752,7 +755,7 @@ pub mod debuginfo {
const FlagPublic = 3;
const FlagFwdDecl = (1 << 2);
const FlagAppleBlock = (1 << 3);
const FlagBlockByrefStruct = (1 << 4);
const FlagReservedBit4 = (1 << 4);
const FlagVirtual = (1 << 5);
const FlagArtificial = (1 << 6);
const FlagExplicit = (1 << 7);
Expand All @@ -763,10 +766,21 @@ pub mod debuginfo {
const FlagStaticMember = (1 << 12);
const FlagLValueReference = (1 << 13);
const FlagRValueReference = (1 << 14);
const FlagExternalTypeRef = (1 << 15);
const FlagReserved = (1 << 15);
const FlagSingleInheritance = (1 << 16);
const FlagMultipleInheritance = (2 << 16);
const FlagVirtualInheritance = (3 << 16);
const FlagIntroducedVirtual = (1 << 18);
const FlagBitField = (1 << 19);
const FlagNoReturn = (1 << 20);
// The bit at (1 << 21) is unused, but was `LLVMDIFlagMainSubprogram`.
const FlagTypePassByValue = (1 << 22);
const FlagTypePassByReference = (1 << 23);
const FlagEnumClass = (1 << 24);
const FlagThunk = (1 << 25);
const FlagNonTrivial = (1 << 26);
const FlagBigEndian = (1 << 27);
const FlagLittleEndian = (1 << 28);
}
}

Expand Down
182 changes: 68 additions & 114 deletions compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@

#include "llvm-c/Analysis.h"
#include "llvm-c/Core.h"
#include "llvm-c/DebugInfo.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
Expand Down Expand Up @@ -676,120 +677,73 @@ template <typename DIT> DIT *unwrapDIPtr(LLVMMetadataRef Ref) {
#define DIArray DINodeArray
#define unwrapDI unwrapDIPtr

// These values **must** match debuginfo::DIFlags! They also *happen*
// to match LLVM, but that isn't required as we do giant sets of
// matching below. The value shouldn't be directly passed to LLVM.
enum class LLVMRustDIFlags : uint32_t {
FlagZero = 0,
FlagPrivate = 1,
FlagProtected = 2,
FlagPublic = 3,
FlagFwdDecl = (1 << 2),
FlagAppleBlock = (1 << 3),
FlagBlockByrefStruct = (1 << 4),
FlagVirtual = (1 << 5),
FlagArtificial = (1 << 6),
FlagExplicit = (1 << 7),
FlagPrototyped = (1 << 8),
FlagObjcClassComplete = (1 << 9),
FlagObjectPointer = (1 << 10),
FlagVector = (1 << 11),
FlagStaticMember = (1 << 12),
FlagLValueReference = (1 << 13),
FlagRValueReference = (1 << 14),
FlagExternalTypeRef = (1 << 15),
FlagIntroducedVirtual = (1 << 18),
FlagBitField = (1 << 19),
FlagNoReturn = (1 << 20),
// Do not add values that are not supported by the minimum LLVM
// version we support! see llvm/include/llvm/IR/DebugInfoFlags.def
};

inline LLVMRustDIFlags operator&(LLVMRustDIFlags A, LLVMRustDIFlags B) {
return static_cast<LLVMRustDIFlags>(static_cast<uint32_t>(A) &
static_cast<uint32_t>(B));
}

inline LLVMRustDIFlags operator|(LLVMRustDIFlags A, LLVMRustDIFlags B) {
return static_cast<LLVMRustDIFlags>(static_cast<uint32_t>(A) |
static_cast<uint32_t>(B));
}

inline LLVMRustDIFlags &operator|=(LLVMRustDIFlags &A, LLVMRustDIFlags B) {
return A = A | B;
}

inline bool isSet(LLVMRustDIFlags F) { return F != LLVMRustDIFlags::FlagZero; }

inline LLVMRustDIFlags visibility(LLVMRustDIFlags F) {
return static_cast<LLVMRustDIFlags>(static_cast<uint32_t>(F) & 0x3);
}

static DINode::DIFlags fromRust(LLVMRustDIFlags Flags) {
DINode::DIFlags Result = DINode::DIFlags::FlagZero;

switch (visibility(Flags)) {
case LLVMRustDIFlags::FlagPrivate:
Result |= DINode::DIFlags::FlagPrivate;
break;
case LLVMRustDIFlags::FlagProtected:
Result |= DINode::DIFlags::FlagProtected;
break;
case LLVMRustDIFlags::FlagPublic:
Result |= DINode::DIFlags::FlagPublic;
break;
default:
// The rest are handled below
break;
}

if (isSet(Flags & LLVMRustDIFlags::FlagFwdDecl)) {
Result |= DINode::DIFlags::FlagFwdDecl;
}
if (isSet(Flags & LLVMRustDIFlags::FlagAppleBlock)) {
Result |= DINode::DIFlags::FlagAppleBlock;
}
if (isSet(Flags & LLVMRustDIFlags::FlagVirtual)) {
Result |= DINode::DIFlags::FlagVirtual;
}
if (isSet(Flags & LLVMRustDIFlags::FlagArtificial)) {
Result |= DINode::DIFlags::FlagArtificial;
}
if (isSet(Flags & LLVMRustDIFlags::FlagExplicit)) {
Result |= DINode::DIFlags::FlagExplicit;
}
if (isSet(Flags & LLVMRustDIFlags::FlagPrototyped)) {
Result |= DINode::DIFlags::FlagPrototyped;
}
if (isSet(Flags & LLVMRustDIFlags::FlagObjcClassComplete)) {
Result |= DINode::DIFlags::FlagObjcClassComplete;
}
if (isSet(Flags & LLVMRustDIFlags::FlagObjectPointer)) {
Result |= DINode::DIFlags::FlagObjectPointer;
}
if (isSet(Flags & LLVMRustDIFlags::FlagVector)) {
Result |= DINode::DIFlags::FlagVector;
}
if (isSet(Flags & LLVMRustDIFlags::FlagStaticMember)) {
Result |= DINode::DIFlags::FlagStaticMember;
}
if (isSet(Flags & LLVMRustDIFlags::FlagLValueReference)) {
Result |= DINode::DIFlags::FlagLValueReference;
}
if (isSet(Flags & LLVMRustDIFlags::FlagRValueReference)) {
Result |= DINode::DIFlags::FlagRValueReference;
}
if (isSet(Flags & LLVMRustDIFlags::FlagIntroducedVirtual)) {
Result |= DINode::DIFlags::FlagIntroducedVirtual;
}
if (isSet(Flags & LLVMRustDIFlags::FlagBitField)) {
Result |= DINode::DIFlags::FlagBitField;
}
if (isSet(Flags & LLVMRustDIFlags::FlagNoReturn)) {
Result |= DINode::DIFlags::FlagNoReturn;
}

return Result;
// FIXME(Zalathar): This is a temporary typedef to avoid churning dozens of
// bindings that are going to be deleted and replaced with their LLVM-C
// equivalents, as part of #134009. After that happens, the remaining bindings
// can be adjusted to use `LLVMDIFlags` instead of relying on this typedef.
typedef LLVMDIFlags LLVMRustDIFlags;

// Statically assert that `LLVMDIFlags` (C) and `DIFlags` (C++) have the same
// layout, at least for the flags we know about. This isn't guaranteed, but is
// likely to remain true, and as long as it is true it makes conversions easy.
#define ASSERT_DIFLAG_VALUE(FLAG, VALUE) \
static_assert((LLVMDI##FLAG == (VALUE)) && (DINode::DIFlags::FLAG == (VALUE)))
ASSERT_DIFLAG_VALUE(FlagZero, 0);
ASSERT_DIFLAG_VALUE(FlagPrivate, 1);
ASSERT_DIFLAG_VALUE(FlagProtected, 2);
ASSERT_DIFLAG_VALUE(FlagPublic, 3);
// Bit (1 << 1) is part of the private/protected/public values above.
ASSERT_DIFLAG_VALUE(FlagFwdDecl, 1 << 2);
ASSERT_DIFLAG_VALUE(FlagAppleBlock, 1 << 3);
ASSERT_DIFLAG_VALUE(FlagReservedBit4, 1 << 4);
ASSERT_DIFLAG_VALUE(FlagVirtual, 1 << 5);
ASSERT_DIFLAG_VALUE(FlagArtificial, 1 << 6);
ASSERT_DIFLAG_VALUE(FlagExplicit, 1 << 7);
ASSERT_DIFLAG_VALUE(FlagPrototyped, 1 << 8);
ASSERT_DIFLAG_VALUE(FlagObjcClassComplete, 1 << 9);
ASSERT_DIFLAG_VALUE(FlagObjectPointer, 1 << 10);
ASSERT_DIFLAG_VALUE(FlagVector, 1 << 11);
ASSERT_DIFLAG_VALUE(FlagStaticMember, 1 << 12);
ASSERT_DIFLAG_VALUE(FlagLValueReference, 1 << 13);
ASSERT_DIFLAG_VALUE(FlagRValueReference, 1 << 14);
// Bit (1 << 15) has been recycled, but the C API value hasn't been renamed.
static_assert((LLVMDIFlagReserved == (1 << 15)) &&
(DINode::DIFlags::FlagExportSymbols == (1 << 15)));
ASSERT_DIFLAG_VALUE(FlagSingleInheritance, 1 << 16);
ASSERT_DIFLAG_VALUE(FlagMultipleInheritance, 2 << 16);
ASSERT_DIFLAG_VALUE(FlagVirtualInheritance, 3 << 16);
// Bit (1 << 17) is part of the inheritance values above.
ASSERT_DIFLAG_VALUE(FlagIntroducedVirtual, 1 << 18);
ASSERT_DIFLAG_VALUE(FlagBitField, 1 << 19);
ASSERT_DIFLAG_VALUE(FlagNoReturn, 1 << 20);
// Bit (1 << 21) is unused, but was `LLVMDIFlagMainSubprogram`.
ASSERT_DIFLAG_VALUE(FlagTypePassByValue, 1 << 22);
ASSERT_DIFLAG_VALUE(FlagTypePassByReference, 1 << 23);
ASSERT_DIFLAG_VALUE(FlagEnumClass, 1 << 24);
ASSERT_DIFLAG_VALUE(FlagThunk, 1 << 25);
ASSERT_DIFLAG_VALUE(FlagNonTrivial, 1 << 26);
ASSERT_DIFLAG_VALUE(FlagBigEndian, 1 << 27);
ASSERT_DIFLAG_VALUE(FlagLittleEndian, 1 << 28);
ASSERT_DIFLAG_VALUE(FlagIndirectVirtualBase, (1 << 2) | (1 << 5));
#undef ASSERT_DIFLAG_VALUE

// There are two potential ways to convert `LLVMDIFlags` to `DIFlags`:
// - Check and copy every individual bit/subvalue from input to output.
// - Statically assert that both have the same layout, and cast.
// As long as the static assertions succeed, a cast is easier and faster.
// In the (hopefully) unlikely event that the assertions do fail someday, and
// LLVM doesn't expose its own conversion function, we'll have to switch over
// to copying each bit/subvalue.
static DINode::DIFlags fromRust(LLVMDIFlags Flags) {
// Check that all set bits are covered by the static assertions above.
const unsigned UNKNOWN_BITS = (1 << 31) | (1 << 30) | (1 << 29) | (1 << 21);
if (Flags & UNKNOWN_BITS) {
report_fatal_error("bad LLVMDIFlags");
}

// As long as the static assertions are satisfied and no unknown bits are
// present, we can convert from `LLVMDIFlags` to `DIFlags` with a cast.
return static_cast<DINode::DIFlags>(Flags);
}

// These values **must** match debuginfo::DISPFlags! They also *happen*
Expand Down

0 comments on commit e0d74c0

Please sign in to comment.