Rollup merge of #136375 - Zalathar:llvm-di-builder, r=workingjubilee

cg_llvm: Replace some DIBuilder wrappers with LLVM-C API bindings (part 1)

Part of #134001, follow-up to #136326, extracted from #134009.

This PR performs an arbitrary subset of the LLVM-C binding migrations from #134009, which should make it less tedious to review. The remaining migrations can occur in one or more subsequent PRs.

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -1,3 +1,15 @@
+//! Bindings to the LLVM-C API (`LLVM*`), and to our own `extern "C"` wrapper
+//! functions around the unstable LLVM C++ API (`LLVMRust*`).
+//!
+//! ## Passing pointer/length strings as `*const c_uchar`
+//!
+//! Normally it's a good idea for Rust-side bindings to match the corresponding
+//! C-side function declarations as closely as possible. But when passing `&str`
+//! or `&[u8]` data as a pointer/length pair, it's more convenient to declare
+//! the Rust-side pointer as `*const c_uchar` instead of `*const c_char`.
+//! Both pointer types have the same ABI, and using `*const c_uchar` avoids
+//! the need for an extra cast from `*const u8` on the Rust side.
+
 #![allow(non_camel_case_types)]
 #![allow(non_upper_case_globals)]
 
@@ -5,17 +17,18 @@ use std::fmt::Debug;
 use std::marker::PhantomData;
 use std::ptr;
 
-use libc::{c_char, c_int, c_uint, c_ulonglong, c_void, size_t};
+use bitflags::bitflags;
+use libc::{c_char, c_int, c_uchar, c_uint, c_ulonglong, c_void, size_t};
 use rustc_macros::TryFromU32;
 use rustc_target::spec::SymbolVisibility;
 
 use super::RustString;
 use super::debuginfo::{
     DIArray, DIBasicType, DIBuilder, DICompositeType, DIDerivedType, DIDescriptor, DIEnumerator,
-    DIFile, DIFlags, DIGlobalVariableExpression, DILexicalBlock, DILocation, DINameSpace,
-    DISPFlags, DIScope, DISubprogram, DISubrange, DITemplateTypeParameter, DIType, DIVariable,
-    DebugEmissionKind, DebugNameTableKind,
+    DIFile, DIFlags, DIGlobalVariableExpression, DILocation, DISPFlags, DIScope, DISubprogram,
+    DISubrange, DITemplateTypeParameter, DIType, DIVariable, DebugEmissionKind, DebugNameTableKind,
 };
+use crate::llvm;
 
 /// In the LLVM-C API, boolean values are passed as `typedef int LLVMBool`,
 /// which has a different ABI from Rust or C++ `bool`.
@@ -789,12 +802,50 @@ pub type DiagnosticHandlerTy = unsafe extern "C" fn(&DiagnosticInfo, *mut c_void
 pub type InlineAsmDiagHandlerTy = unsafe extern "C" fn(&SMDiagnostic, *const c_void, c_uint);
 
 pub mod debuginfo {
+    use std::ptr;
+
     use bitflags::bitflags;
 
     use super::{InvariantOpaque, Metadata};
+    use crate::llvm::{self, Module};
 
+    /// Opaque target type for references to an LLVM debuginfo builder.
+    ///
+    /// `&'_ DIBuilder<'ll>` corresponds to `LLVMDIBuilderRef`, which is the
+    /// LLVM-C wrapper for `DIBuilder *`.
+    ///
+    /// Debuginfo builders are created and destroyed during codegen, so the
+    /// builder reference typically has a shorter lifetime than the LLVM
+    /// session (`'ll`) that it participates in.
     #[repr(C)]
-    pub struct DIBuilder<'a>(InvariantOpaque<'a>);
+    pub struct DIBuilder<'ll>(InvariantOpaque<'ll>);
+
+    /// Owning pointer to a `DIBuilder<'ll>` that will dispose of the builder
+    /// when dropped. Use `.as_ref()` to get the underlying `&DIBuilder`
+    /// needed for debuginfo FFI calls.
+    pub(crate) struct DIBuilderBox<'ll> {
+        raw: ptr::NonNull<DIBuilder<'ll>>,
+    }
+
+    impl<'ll> DIBuilderBox<'ll> {
+        pub(crate) fn new(llmod: &'ll Module) -> Self {
+            let raw = unsafe { llvm::LLVMCreateDIBuilder(llmod) };
+            let raw = ptr::NonNull::new(raw).unwrap();
+            Self { raw }
+        }
+
+        pub(crate) fn as_ref(&self) -> &DIBuilder<'ll> {
+            // SAFETY: This is an owning pointer, so `&DIBuilder` is valid
+            // for as long as `&self` is.
+            unsafe { self.raw.as_ref() }
+        }
+    }
+
+    impl<'ll> Drop for DIBuilderBox<'ll> {
+        fn drop(&mut self) {
+            unsafe { llvm::LLVMDisposeDIBuilder(self.raw) };
+        }
+    }
 
     pub type DIDescriptor = Metadata;
     pub type DILocation = Metadata;
@@ -914,7 +965,6 @@ pub mod debuginfo {
     }
 }
 
-use bitflags::bitflags;
 // These values **must** match with LLVMRustAllocKindFlags
 bitflags! {
     #[repr(transparent)]
@@ -1675,6 +1725,50 @@ unsafe extern "C" {
     ) -> &'a Value;
 }
 
+// FFI bindings for `DIBuilder` functions in the LLVM-C API.
+// Try to keep these in the same order as in `llvm/include/llvm-c/DebugInfo.h`.
+//
+// FIXME(#134001): Audit all `Option` parameters, especially in lists, to check
+// that they really are nullable on the C/C++ side. LLVM doesn't appear to
+// actually document which ones are nullable.
+unsafe extern "C" {
+    pub(crate) fn LLVMCreateDIBuilder<'ll>(M: &'ll Module) -> *mut DIBuilder<'ll>;
+    pub(crate) fn LLVMDisposeDIBuilder<'ll>(Builder: ptr::NonNull<DIBuilder<'ll>>);
+
+    pub(crate) fn LLVMDIBuilderFinalize<'ll>(Builder: &DIBuilder<'ll>);
+
+    pub(crate) fn LLVMDIBuilderCreateNameSpace<'ll>(
+        Builder: &DIBuilder<'ll>,
+        ParentScope: Option<&'ll Metadata>,
+        Name: *const c_uchar,
+        NameLen: size_t,
+        ExportSymbols: llvm::Bool,
+    ) -> &'ll Metadata;
+
+    pub(crate) fn LLVMDIBuilderCreateLexicalBlock<'ll>(
+        Builder: &DIBuilder<'ll>,
+        Scope: &'ll Metadata,
+        File: &'ll Metadata,
+        Line: c_uint,
+        Column: c_uint,
+    ) -> &'ll Metadata;
+
+    pub(crate) fn LLVMDIBuilderCreateLexicalBlockFile<'ll>(
+        Builder: &DIBuilder<'ll>,
+        Scope: &'ll Metadata,
+        File: &'ll Metadata,
+        Discriminator: c_uint, // (optional "DWARF path discriminator"; default is 0)
+    ) -> &'ll Metadata;
+
+    pub(crate) fn LLVMDIBuilderCreateDebugLocation<'ll>(
+        Ctx: &'ll Context,
+        Line: c_uint,
+        Column: c_uint,
+        Scope: &'ll Metadata,
+        InlinedAt: Option<&'ll Metadata>,
+    ) -> &'ll Metadata;
+}
+
 #[link(name = "llvm-wrapper", kind = "static")]
 unsafe extern "C" {
     pub fn LLVMRustInstallErrorHandlers();
@@ -1942,12 +2036,6 @@ unsafe extern "C" {
         ValueLen: size_t,
     );
 
-    pub fn LLVMRustDIBuilderCreate(M: &Module) -> &mut DIBuilder<'_>;
-
-    pub fn LLVMRustDIBuilderDispose<'a>(Builder: &'a mut DIBuilder<'a>);
-
-    pub fn LLVMRustDIBuilderFinalize(Builder: &DIBuilder<'_>);
-
     pub fn LLVMRustDIBuilderCreateCompileUnit<'a>(
         Builder: &DIBuilder<'a>,
         Lang: c_uint,
@@ -2110,20 +2198,6 @@ unsafe extern "C" {
         Type: &'a DIType,
     ) -> &'a DIDerivedType;
 
-    pub fn LLVMRustDIBuilderCreateLexicalBlock<'a>(
-        Builder: &DIBuilder<'a>,
-        Scope: &'a DIScope,
-        File: &'a DIFile,
-        Line: c_uint,
-        Col: c_uint,
-    ) -> &'a DILexicalBlock;
-
-    pub fn LLVMRustDIBuilderCreateLexicalBlockFile<'a>(
-        Builder: &DIBuilder<'a>,
-        Scope: &'a DIScope,
-        File: &'a DIFile,
-    ) -> &'a DILexicalBlock;
-
     pub fn LLVMRustDIBuilderCreateStaticVariable<'a>(
         Builder: &DIBuilder<'a>,
         Context: Option<&'a DIScope>,
@@ -2248,14 +2322,6 @@ unsafe extern "C" {
         Ty: &'a DIType,
     ) -> &'a DITemplateTypeParameter;
 
-    pub fn LLVMRustDIBuilderCreateNameSpace<'a>(
-        Builder: &DIBuilder<'a>,
-        Scope: Option<&'a DIScope>,
-        Name: *const c_char,
-        NameLen: size_t,
-        ExportSymbols: bool,
-    ) -> &'a DINameSpace;
-
     pub fn LLVMRustDICompositeTypeReplaceArrays<'a>(
         Builder: &DIBuilder<'a>,
         CompositeType: &'a DIType,
@@ -2263,12 +2329,6 @@ unsafe extern "C" {
         Params: Option<&'a DIArray>,
     );
 
-    pub fn LLVMRustDIBuilderCreateDebugLocation<'a>(
-        Line: c_uint,
-        Column: c_uint,
-        Scope: &'a DIScope,
-        InlinedAt: Option<&'a DILocation>,
-    ) -> &'a DILocation;
     pub fn LLVMRustDILocationCloneWithBaseDiscriminator<'a>(
         Location: &'a DILocation,
         BD: c_uint,