Use constants for DWARF opcodes, instead of FFI calls

Author: Zalathar

compiler/rustc_codegen_llvm/src/debuginfo/dwarf_const.rs

@@ -16,3 +16,11 @@ pub(crate) const DW_ATE_float: c_uint = 0x04;
 pub(crate) const DW_ATE_signed: c_uint = 0x05;
 pub(crate) const DW_ATE_unsigned: c_uint = 0x07;
 pub(crate) const DW_ATE_UTF: c_uint = 0x10;
+
+// DWARF expression operators
+
+pub(crate) const DW_OP_deref: u64 = 0x06;
+pub(crate) const DW_OP_plus_uconst: u64 = 0x23;
+/// Defined by LLVM in `llvm/include/llvm/BinaryFormat/Dwarf.h`.
+/// Double-checked by a static assertion in `RustWrapper.cpp`.
+pub(crate) const DW_OP_LLVM_fragment: u64 = 0x1000;

compiler/rustc_codegen_llvm/src/debuginfo/mod.rs

@@ -153,29 +153,26 @@ impl<'ll> DebugInfoBuilderMethods for Builder<'_, 'll, '_> {
         indirect_offsets: &[Size],
         fragment: Option<Range<Size>>,
     ) {
+        use dwarf_const::{DW_OP_LLVM_fragment, DW_OP_deref, DW_OP_plus_uconst};
+
         // Convert the direct and indirect offsets and fragment byte range to address ops.
-        // FIXME(eddyb) use `const`s instead of getting the values via FFI,
-        // the values should match the ones in the DWARF standard anyway.
-        let op_deref = || unsafe { llvm::LLVMRustDIBuilderCreateOpDeref() };
-        let op_plus_uconst = || unsafe { llvm::LLVMRustDIBuilderCreateOpPlusUconst() };
-        let op_llvm_fragment = || unsafe { llvm::LLVMRustDIBuilderCreateOpLLVMFragment() };
         let mut addr_ops = SmallVec::<[u64; 8]>::new();
 
         if direct_offset.bytes() > 0 {
-            addr_ops.push(op_plus_uconst());
+            addr_ops.push(DW_OP_plus_uconst);
             addr_ops.push(direct_offset.bytes() as u64);
         }
         for &offset in indirect_offsets {
-            addr_ops.push(op_deref());
+            addr_ops.push(DW_OP_deref);
             if offset.bytes() > 0 {
-                addr_ops.push(op_plus_uconst());
+                addr_ops.push(DW_OP_plus_uconst);
                 addr_ops.push(offset.bytes() as u64);
             }
         }
         if let Some(fragment) = fragment {
             // `DW_OP_LLVM_fragment` takes as arguments the fragment's
             // offset and size, both of them in bits.
-            addr_ops.push(op_llvm_fragment());
+            addr_ops.push(DW_OP_LLVM_fragment);
             addr_ops.push(fragment.start.bits() as u64);
             addr_ops.push((fragment.end - fragment.start).bits() as u64);
         }

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -2171,9 +2171,6 @@ unsafe extern "C" {
         Location: &'a DILocation,
         BD: c_uint,
     ) -> Option<&'a DILocation>;
-    pub fn LLVMRustDIBuilderCreateOpDeref() -> u64;
-    pub fn LLVMRustDIBuilderCreateOpPlusUconst() -> u64;
-    pub fn LLVMRustDIBuilderCreateOpLLVMFragment() -> u64;
 
     pub fn LLVMRustWriteTypeToString(Type: &Type, s: &RustString);
     pub fn LLVMRustWriteValueToString(value_ref: &Value, s: &RustString);

compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp

@@ -54,6 +54,12 @@ using namespace llvm;
 using namespace llvm::sys;
 using namespace llvm::object;
 
+// This opcode is an LLVM detail that could hypothetically change, so verify
+// that the hard-coded value in `dwarf_const.rs` still agrees with LLVM.
+static_assert(
+    dwarf::DW_OP_LLVM_fragment == 0x1000,
+    "DW_OP_LLVM_fragment has changed from the value used by Rust-side code");
+
 // LLVMAtomicOrdering is already an enum - don't create another
 // one.
 static AtomicOrdering fromRust(LLVMAtomicOrdering Ordering) {
@@ -1390,18 +1396,6 @@ LLVMRustDILocationCloneWithBaseDiscriminator(LLVMMetadataRef Location,
   return wrap(NewLoc.has_value() ? NewLoc.value() : nullptr);
 }
 
-extern "C" uint64_t LLVMRustDIBuilderCreateOpDeref() {
-  return dwarf::DW_OP_deref;
-}
-
-extern "C" uint64_t LLVMRustDIBuilderCreateOpPlusUconst() {
-  return dwarf::DW_OP_plus_uconst;
-}
-
-extern "C" uint64_t LLVMRustDIBuilderCreateOpLLVMFragment() {
-  return dwarf::DW_OP_LLVM_fragment;
-}
-
 extern "C" void LLVMRustWriteTypeToString(LLVMTypeRef Ty, RustStringRef Str) {
   auto OS = RawRustStringOstream(Str);
   unwrap<llvm::Type>(Ty)->print(OS);