cg_llvm/debuginfo: scalable vectors

Generate debuginfo for scalable vectors, following the structure that
Clang generates for scalable vectors.

Author: davidtwco

compiler/rustc_abi/src/lib.rs

@@ -1763,6 +1763,16 @@ impl NumScalableVectors {
             _ => None,
         }
     }
+
+    /// Returns number of scalable vectors as a `u64`.
+    pub fn as_u64(self) -> u64 {
+        match self {
+            NumScalableVectors::One => 1,
+            NumScalableVectors::Two => 2,
+            NumScalableVectors::Three => 3,
+            NumScalableVectors::Four => 4,
+        }
+    }
 }
 
 /// The way we represent values to the backend

compiler/rustc_codegen_gcc/src/common.rs

@@ -144,6 +144,10 @@ impl<'gcc, 'tcx> ConstCodegenMethods for CodegenCx<'gcc, 'tcx> {
         self.const_int(self.type_i32(), i as i64)
     }
 
+    fn const_i64(&self, i: i64) -> RValue<'gcc> {
+        self.const_int(self.type_i64(), i)
+    }
+
     fn const_int(&self, typ: Type<'gcc>, int: i64) -> RValue<'gcc> {
         self.gcc_int(typ, int)
     }

compiler/rustc_codegen_llvm/src/common.rs

@@ -159,6 +159,10 @@ impl<'ll, 'tcx> ConstCodegenMethods for CodegenCx<'ll, 'tcx> {
         self.const_int(self.type_i32(), i as i64)
     }
 
+    fn const_i64(&self, i: i64) -> &'ll Value {
+        self.const_int(self.type_i64(), i as i64)
+    }
+
     fn const_int(&self, t: &'ll Type, i: i64) -> &'ll Value {
         debug_assert!(
             self.type_kind(t) == TypeKind::Integer,

compiler/rustc_codegen_llvm/src/debuginfo/dwarf_const.rs

@@ -35,6 +35,14 @@ declare_constant!(DW_OP_plus_uconst: u64);
 /// Double-checked by a static assertion in `RustWrapper.cpp`.
 #[allow(non_upper_case_globals)]
 pub(crate) const DW_OP_LLVM_fragment: u64 = 0x1000;
+#[allow(non_upper_case_globals)]
+pub(crate) const DW_OP_constu: u64 = 0x10;
+#[allow(non_upper_case_globals)]
+pub(crate) const DW_OP_minus: u64 = 0x1c;
+#[allow(non_upper_case_globals)]
+pub(crate) const DW_OP_mul: u64 = 0x1e;
+#[allow(non_upper_case_globals)]
+pub(crate) const DW_OP_bregx: u64 = 0x92;
 // It describes the actual value of a source variable which might not exist in registers or in memory.
 #[allow(non_upper_case_globals)]
 pub(crate) const DW_OP_stack_value: u64 = 0x9f;

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -6,7 +6,7 @@ use std::sync::Arc;
 use std::{iter, ptr};
 
 use libc::{c_longlong, c_uint};
-use rustc_abi::{Align, Size};
+use rustc_abi::{Align, Layout, NumScalableVectors, Size};
 use rustc_codegen_ssa::debuginfo::type_names::{VTableNameKind, cpp_like_debuginfo};
 use rustc_codegen_ssa::traits::*;
 use rustc_hir::def::{CtorKind, DefKind};
@@ -16,7 +16,7 @@ use rustc_middle::ty::layout::{
     HasTypingEnv, LayoutOf, TyAndLayout, WIDE_PTR_ADDR, WIDE_PTR_EXTRA,
 };
 use rustc_middle::ty::{
-    self, AdtKind, CoroutineArgsExt, ExistentialTraitRef, Instance, Ty, TyCtxt, Visibility,
+    self, AdtDef, AdtKind, CoroutineArgsExt, ExistentialTraitRef, Instance, Ty, TyCtxt, Visibility,
 };
 use rustc_session::config::{self, DebugInfo, Lto};
 use rustc_span::{DUMMY_SP, FileName, RemapPathScopeComponents, SourceFile, Span, Symbol, hygiene};
@@ -33,7 +33,7 @@ use super::type_names::{compute_debuginfo_type_name, compute_debuginfo_vtable_na
 use super::utils::{DIB, debug_context, get_namespace_for_item, is_node_local_to_unit};
 use crate::common::{AsCCharPtr, CodegenCx};
 use crate::debuginfo::metadata::type_map::build_type_with_children;
-use crate::debuginfo::utils::{WidePtrKind, wide_pointer_kind};
+use crate::debuginfo::utils::{WidePtrKind, create_DIArray, wide_pointer_kind};
 use crate::debuginfo::{DIBuilderExt, dwarf_const};
 use crate::llvm::debuginfo::{
     DIBasicType, DIBuilder, DICompositeType, DIDescriptor, DIFile, DIFlags, DILexicalBlock,
@@ -1040,6 +1040,7 @@ fn build_struct_type_di_node<'ll, 'tcx>(
     span: Span,
 ) -> DINodeCreationResult<'ll> {
     let struct_type = unique_type_id.expect_ty();
+
     let ty::Adt(adt_def, _) = struct_type.kind() else {
         bug!("build_struct_type_di_node() called with non-struct-type: {:?}", struct_type);
     };
@@ -1052,14 +1053,29 @@ fn build_struct_type_di_node<'ll, 'tcx>(
     } else {
         None
     };
+    let name = compute_debuginfo_type_name(cx.tcx, struct_type, false);
+
+    if struct_type.is_scalable_vector() {
+        let parts = struct_type.scalable_vector_parts(cx.tcx).unwrap();
+        return build_scalable_vector_di_node(
+            cx,
+            unique_type_id,
+            name,
+            *adt_def,
+            parts,
+            struct_type_and_layout.layout,
+            def_location,
+            containing_scope,
+        );
+    }
 
     type_map::build_type_with_children(
         cx,
         type_map::stub(
             cx,
             Stub::Struct,
             unique_type_id,
-            &compute_debuginfo_type_name(cx.tcx, struct_type, false),
+            &name,
             def_location,
             size_and_align_of(struct_type_and_layout),
             Some(containing_scope),
@@ -1102,6 +1118,97 @@ fn build_struct_type_di_node<'ll, 'tcx>(
     )
 }
 
+/// Generate debuginfo for a `#[rustc_scalable_vector]` type.
+///
+/// Debuginfo for a scalable vector takes the form of a derived type with a composite base type
+/// with `DIFlagVector` that itself has a base type of whatever the element of the scalable vector
+/// is. The composite type has a subrange from 0 to an expression that calculates the number of
+/// elements in the vector.
+///
+/// ```text, ignore
+/// !1 = !DIDerivedType(tag: DW_TAG_typedef, name: "svint16_t", ..., baseType: !2, ...)
+/// !2 = !DICompositeType(tag: DW_TAG_array_type, baseType: !3, ..., flags: DIFlagVector, elements: !4)
+/// !3 = !DIBasicType(name: "i16", size: 16, encoding: DW_ATE_signed)
+/// !4 = !{!5}
+/// !5 = !DISubrange(lowerBound: 0, upperBound: !DIExpression(DW_OP_constu, 4, DW_OP_bregx, 46, 0, DW_OP_mul, DW_OP_constu, 1, DW_OP_minus))
+/// ```
+///
+/// See the `CodegenType::CreateType(const BuiltinType *BT)` implementation in Clang for how this
+/// is generated for C and C++.
+fn build_scalable_vector_di_node<'ll, 'tcx>(
+    cx: &CodegenCx<'ll, 'tcx>,
+    unique_type_id: UniqueTypeId<'tcx>,
+    name: String,
+    adt_def: AdtDef<'tcx>,
+    (element_count, element_ty, number_of_vectors): (u16, Ty<'tcx>, NumScalableVectors),
+    layout: Layout<'tcx>,
+    def_location: Option<DefinitionLocation<'ll>>,
+    containing_scope: &'ll DIScope,
+) -> DINodeCreationResult<'ll> {
+    use dwarf_const::{DW_OP_bregx, DW_OP_constu, DW_OP_minus, DW_OP_mul};
+    assert!(adt_def.repr().scalable());
+
+    let (file_metadata, line_number) = if let Some(def_location) = def_location {
+        (def_location.0, def_location.1)
+    } else {
+        (unknown_file_metadata(cx), UNKNOWN_LINE_NUMBER)
+    };
+
+    let (bitstride, element_di_node) = if element_ty.is_bool() {
+        (Some(llvm::LLVMValueAsMetadata(cx.const_i64(1))), type_di_node(cx, cx.tcx.types.u8))
+    } else {
+        (None, type_di_node(cx, element_ty))
+    };
+
+    let number_of_elements: u64 = (element_count as u64) * number_of_vectors.as_u64();
+    let number_of_elements_per_vg = number_of_elements / 2;
+    let mut expr = smallvec::SmallVec::<[u64; 9]>::new();
+    // `($number_of_elements_per_vector_granule * (value_of_register(AArch64::VG) + 0)) - 1`
+    expr.push(DW_OP_constu); // Push a constant onto the stack
+    expr.push(number_of_elements_per_vg);
+    expr.push(DW_OP_bregx); // Push the value of a register + offset on to the stack
+    expr.push(/* AArch64::VG */ 46u64);
+    expr.push(0u64);
+    expr.push(DW_OP_mul); // Multiply top two values on stack
+    expr.push(DW_OP_constu); // Push a constant onto the stack
+    expr.push(1u64);
+    expr.push(DW_OP_minus); // Subtract top two values on stack
+
+    let di_builder = DIB(cx);
+    let metadata = unsafe {
+        let upper = llvm::LLVMDIBuilderCreateExpression(di_builder, expr.as_ptr(), expr.len());
+        let subrange = llvm::LLVMRustDIGetOrCreateSubrange(
+            di_builder,
+            /* CountNode */ None,
+            llvm::LLVMValueAsMetadata(cx.const_i64(0)),
+            upper,
+            /* Stride */ None,
+        );
+        let subscripts = create_DIArray(di_builder, &[Some(subrange)]);
+        let vector_ty = llvm::LLVMRustDICreateVectorType(
+            di_builder,
+            /* Size */ 0,
+            layout.align.bits() as u32,
+            element_di_node,
+            subscripts,
+            bitstride,
+        );
+        llvm::LLVMDIBuilderCreateTypedef(
+            di_builder,
+            vector_ty,
+            name.as_ptr(),
+            name.len(),
+            file_metadata,
+            line_number,
+            Some(containing_scope),
+            layout.align.bits() as u32,
+        )
+    };
+
+    debug_context(cx).type_map.insert(unique_type_id, metadata);
+    DINodeCreationResult { di_node: metadata, already_stored_in_typemap: true }
+}
+
 //=-----------------------------------------------------------------------------
 // Tuples
 //=-----------------------------------------------------------------------------

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -2302,6 +2302,23 @@ unsafe extern "C" {
         Params: Option<&'a DIArray>,
     );
 
+    pub(crate) fn LLVMRustDIGetOrCreateSubrange<'a>(
+        Builder: &DIBuilder<'a>,
+        CountNode: Option<&'a Metadata>,
+        LB: &'a Metadata,
+        UB: &'a Metadata,
+        Stride: Option<&'a Metadata>,
+    ) -> &'a Metadata;
+
+    pub(crate) fn LLVMRustDICreateVectorType<'a>(
+        Builder: &DIBuilder<'a>,
+        Size: u64,
+        AlignInBits: u32,
+        Type: &'a DIType,
+        Subscripts: &'a DIArray,
+        BitStride: Option<&'a Metadata>,
+    ) -> &'a Metadata;
+
     pub(crate) fn LLVMRustDILocationCloneWithBaseDiscriminator<'a>(
         Location: &'a DILocation,
         BD: c_uint,

compiler/rustc_codegen_ssa/src/traits/consts.rs

@@ -20,6 +20,7 @@ pub trait ConstCodegenMethods: BackendTypes {
     fn const_i8(&self, i: i8) -> Self::Value;
     fn const_i16(&self, i: i16) -> Self::Value;
     fn const_i32(&self, i: i32) -> Self::Value;
+    fn const_i64(&self, i: i64) -> Self::Value;
     fn const_int(&self, t: Self::Type, i: i64) -> Self::Value;
     fn const_u8(&self, i: u8) -> Self::Value;
     fn const_u32(&self, i: u32) -> Self::Value;

compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp

@@ -70,6 +70,10 @@ 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);
+static_assert(dwarf::DW_OP_constu == 0x10);
+static_assert(dwarf::DW_OP_minus == 0x1c);
+static_assert(dwarf::DW_OP_mul == 0x1e);
+static_assert(dwarf::DW_OP_bregx == 0x92);
 static_assert(dwarf::DW_OP_stack_value == 0x9f);
 
 static LLVM_THREAD_LOCAL char *LastError;
@@ -734,7 +738,7 @@ extern "C" bool LLVMRustInlineAsmVerify(LLVMTypeRef Ty, char *Constraints,
 }
 
 template <typename DIT> DIT *unwrapDIPtr(LLVMMetadataRef Ref) {
-  return (DIT *)(Ref ? unwrap<MDNode>(Ref) : nullptr);
+  return (DIT *)(Ref ? unwrap<Metadata>(Ref) : nullptr);
 }
 
 #define DIDescriptor DIScope
@@ -1210,6 +1214,24 @@ extern "C" void LLVMRustDICompositeTypeReplaceArrays(
                                  DINodeArray(unwrap<MDTuple>(Params)));
 }
 
+// LLVM's C FFI bindings don't expose the overload of `GetOrCreateSubrange` which takes a metadata
+// node as the upper bound.
+extern "C" LLVMMetadataRef LLVMRustDIGetOrCreateSubrange(
+    LLVMDIBuilderRef Builder, LLVMMetadataRef CountNode, LLVMMetadataRef LB, LLVMMetadataRef UB,
+    LLVMMetadataRef Stride) {
+  return wrap(unwrap(Builder)->getOrCreateSubrange(
+      unwrapDI<Metadata>(CountNode), unwrapDI<Metadata>(LB),
+      unwrapDI<Metadata>(UB), unwrapDI<Metadata>(Stride)));
+}
+
+// LLVM's CI FFI bindings don't expose the `BitStride` parameter of `createVectorType`.
+extern "C" LLVMMetadataRef LLVMRustDICreateVectorType(
+    LLVMDIBuilderRef Builder, uint64_t Size, uint32_t AlignInBits,
+    LLVMMetadataRef Type, LLVMMetadataRef Subscripts, LLVMMetadataRef BitStride) {
+  return wrap(unwrap(Builder)->createVectorType(Size, AlignInBits, unwrapDI<DIType>(Type),
+      DINodeArray(unwrapDI<MDTuple>(Subscripts)), unwrapDI<Metadata>(BitStride)));
+}
+
 extern "C" LLVMMetadataRef
 LLVMRustDILocationCloneWithBaseDiscriminator(LLVMMetadataRef Location,
                                              unsigned BD) {