Rollup merge of #135156 - Zalathar:debuginfo-flags, r=cuviper

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.

3 files changed, 87 insertions, 117 deletions

diff --git a/compiler/rustc_codegen_llvm/Cargo.toml b/compiler/rustc_codegen_llvm/Cargo.toml
index c44d1a5e5c2..94f21ac5f57 100644
--- a/compiler/rustc_codegen_llvm/Cargo.toml
+++ b/compiler/rustc_codegen_llvm/Cargo.toml
@@ -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"
diff --git a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
index 9349ae212d2..009d15a932f 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
@@ -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 {
@@ -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);
@@ -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);
         }
     }
 
diff --git a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp b/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
index dd72ea2497f..35186778671 100644
--- a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
+++ b/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
@@ -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"
@@ -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*