codegen_llvm: avoid Deref impls w/ extern type

`rustc_codegen_llvm` relied on `Deref` impls where `Deref::Target` was
or contained an extern type - in my experimental implementation of
rust-lang/rfcs#3729, this isn't possible as the `Target` associated
type's `?Sized` bound cannot be relaxed backwards compatibly (unless we
come up with some way of doing this).

In later pull requests with the rust-lang/rfcs#3729 implementation,
breakage like this could only occur for nightly users relying on the
`extern_types` feature.

Upstreaming this to avoid needing to keep carrying this patch locally,
and I think it'll necessarily need to change eventually.

Author: davidtwco

compiler/rustc_codegen_llvm/src/back/lto.rs

@@ -793,7 +793,9 @@ pub(crate) unsafe fn optimize_thin_module(
         {
             let _timer =
                 cgcx.prof.generic_activity_with_arg("LLVM_thin_lto_rename", thin_module.name());
-            unsafe { llvm::LLVMRustPrepareThinLTORename(thin_module.shared.data.0, llmod, target) };
+            unsafe {
+                llvm::LLVMRustPrepareThinLTORename(thin_module.shared.data.0, llmod, target.raw())
+            };
             save_temp_bitcode(cgcx, &module, "thin-lto-after-rename");
         }
 
@@ -823,7 +825,7 @@ pub(crate) unsafe fn optimize_thin_module(
             let _timer =
                 cgcx.prof.generic_activity_with_arg("LLVM_thin_lto_import", thin_module.name());
             if unsafe {
-                !llvm::LLVMRustPrepareThinLTOImport(thin_module.shared.data.0, llmod, target)
+                !llvm::LLVMRustPrepareThinLTOImport(thin_module.shared.data.0, llmod, target.raw())
             } {
                 return Err(write::llvm_err(dcx, LlvmError::PrepareThinLtoModule));
             }

compiler/rustc_codegen_llvm/src/back/owned_target_machine.rs

@@ -1,6 +1,5 @@
 use std::ffi::{CStr, c_char};
 use std::marker::PhantomData;
-use std::ops::Deref;
 use std::ptr::NonNull;
 
 use rustc_data_structures::small_c_str::SmallCStr;
@@ -80,12 +79,12 @@ impl OwnedTargetMachine {
             .map(|tm_unique| Self { tm_unique, phantom: PhantomData })
             .ok_or_else(|| LlvmError::CreateTargetMachine { triple: SmallCStr::from(triple) })
     }
-}
-
-impl Deref for OwnedTargetMachine {
-    type Target = llvm::TargetMachine;
 
-    fn deref(&self) -> &Self::Target {
+    /// Returns inner `llvm::TargetMachine` type.
+    ///
+    /// This could be a `Deref` implementation, but `llvm::TargetMachine` is an extern type and
+    /// `Deref::Target: ?Sized`.
+    pub fn raw(&self) -> &llvm::TargetMachine {
         // SAFETY: constructing ensures we have a valid pointer created by
         // llvm::LLVMRustCreateTargetMachine.
         unsafe { self.tm_unique.as_ref() }

compiler/rustc_codegen_llvm/src/back/write.rs

@@ -637,7 +637,7 @@ pub(crate) unsafe fn llvm_optimize(
     let result = unsafe {
         llvm::LLVMRustOptimize(
             module.module_llvm.llmod(),
-            &*module.module_llvm.tm,
+            &*module.module_llvm.tm.raw(),
             to_pass_builder_opt_level(opt_level),
             opt_stage,
             cgcx.opts.cg.linker_plugin_lto.enabled(),
@@ -875,7 +875,7 @@ pub(crate) unsafe fn codegen(
             };
             write_output_file(
                 dcx,
-                tm,
+                tm.raw(),
                 config.no_builtins,
                 llmod,
                 &path,
@@ -909,7 +909,7 @@ pub(crate) unsafe fn codegen(
 
                 write_output_file(
                     dcx,
-                    tm,
+                    tm.raw(),
                     config.no_builtins,
                     llmod,
                     &obj_out,

compiler/rustc_codegen_llvm/src/builder.rs

@@ -405,7 +405,7 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
 
         // Emit KCFI operand bundle
         let kcfi_bundle = self.kcfi_operand_bundle(fn_attrs, fn_abi, instance, llfn);
-        if let Some(kcfi_bundle) = kcfi_bundle.as_deref() {
+        if let Some(kcfi_bundle) = kcfi_bundle.as_ref().map(|b| b.raw()) {
             bundles.push(kcfi_bundle);
         }
 
@@ -1433,7 +1433,7 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
 
         // Emit KCFI operand bundle
         let kcfi_bundle = self.kcfi_operand_bundle(fn_attrs, fn_abi, instance, llfn);
-        if let Some(kcfi_bundle) = kcfi_bundle.as_deref() {
+        if let Some(kcfi_bundle) = kcfi_bundle.as_ref().map(|b| b.raw()) {
             bundles.push(kcfi_bundle);
         }
 
@@ -1782,7 +1782,7 @@ impl<'a, 'll, 'tcx> Builder<'a, 'll, 'tcx> {
 
         // Emit KCFI operand bundle
         let kcfi_bundle = self.kcfi_operand_bundle(fn_attrs, fn_abi, instance, llfn);
-        if let Some(kcfi_bundle) = kcfi_bundle.as_deref() {
+        if let Some(kcfi_bundle) = kcfi_bundle.as_ref().map(|b| b.raw()) {
             bundles.push(kcfi_bundle);
         }
 

compiler/rustc_codegen_llvm/src/common.rs

@@ -77,7 +77,7 @@ impl<'ll> Funclet<'ll> {
     }
 
     pub(crate) fn bundle(&self) -> &llvm::OperandBundle<'ll> {
-        &self.operand
+        self.operand.raw()
     }
 }
 

compiler/rustc_codegen_llvm/src/context.rs

@@ -205,7 +205,7 @@ pub(crate) unsafe fn create_module<'ll>(
     {
         let tm = crate::back::write::create_informational_target_machine(tcx.sess, false);
         unsafe {
-            llvm::LLVMRustSetDataLayoutFromTargetMachine(llmod, &tm);
+            llvm::LLVMRustSetDataLayoutFromTargetMachine(llmod, tm.raw());
         }
 
         let llvm_data_layout = unsafe { llvm::LLVMGetDataLayoutStr(llmod) };

compiler/rustc_codegen_llvm/src/llvm/mod.rs

@@ -1,7 +1,6 @@
 #![allow(non_snake_case)]
 
 use std::ffi::{CStr, CString};
-use std::ops::Deref;
 use std::ptr;
 use std::str::FromStr;
 use std::string::FromUtf8Error;
@@ -355,6 +354,16 @@ impl<'a> OperandBundleOwned<'a> {
         };
         OperandBundleOwned { raw: ptr::NonNull::new(raw).unwrap() }
     }
+
+    /// Returns inner `OperandBundle` type.
+    ///
+    /// This could be a `Deref` implementation, but `OperandBundle` contains an extern type and
+    /// `Deref::Target: ?Sized`.
+    pub(crate) fn raw(&self) -> &OperandBundle<'a> {
+        // SAFETY: The returned reference is opaque and can only used for FFI.
+        // It is valid for as long as `&self` is.
+        unsafe { self.raw.as_ref() }
+    }
 }
 
 impl Drop for OperandBundleOwned<'_> {
@@ -365,16 +374,6 @@ impl Drop for OperandBundleOwned<'_> {
     }
 }
 
-impl<'a> Deref for OperandBundleOwned<'a> {
-    type Target = OperandBundle<'a>;
-
-    fn deref(&self) -> &Self::Target {
-        // SAFETY: The returned reference is opaque and can only used for FFI.
-        // It is valid for as long as `&self` is.
-        unsafe { self.raw.as_ref() }
-    }
-}
-
 pub(crate) fn add_module_flag_u32(
     module: &Module,
     merge_behavior: ModuleFlagMergeBehavior,

compiler/rustc_codegen_llvm/src/llvm_util.rs

@@ -331,7 +331,8 @@ pub(crate) fn target_features_cfg(sess: &Session, allow_unstable: bool) -> Vec<S
                 if let Some(feat) = to_llvm_features(sess, feature) {
                     for llvm_feature in feat {
                         let cstr = SmallCStr::new(llvm_feature);
-                        if !unsafe { llvm::LLVMRustHasFeature(&target_machine, cstr.as_ptr()) } {
+                        if !unsafe { llvm::LLVMRustHasFeature(target_machine.raw(), cstr.as_ptr()) }
+                        {
                             return false;
                         }
                     }
@@ -453,8 +454,8 @@ pub(crate) fn print(req: &PrintRequest, out: &mut String, sess: &Session) {
     require_inited();
     let tm = create_informational_target_machine(sess, false);
     match req.kind {
-        PrintKind::TargetCPUs => print_target_cpus(sess, &tm, out),
-        PrintKind::TargetFeatures => print_target_features(sess, &tm, out),
+        PrintKind::TargetCPUs => print_target_cpus(sess, tm.raw(), out),
+        PrintKind::TargetFeatures => print_target_features(sess, tm.raw(), out),
         _ => bug!("rustc_codegen_llvm can't handle print request: {:?}", req),
     }
 }