Fix static relocation model for PowerPC64

We now also use `should_assume_dso_local()` for declarations and port two
additional cases from clang:
- Exclude PPC64 [1]
- Exclude thread-local variables [2]

[1]: https://github.com/llvm/llvm-project/blob/033138ea452f5f493fb5095e5963419905ad12e1/clang/lib/CodeGen/CodeGenModule.cpp#L1038-L1040
[2]: https://github.com/llvm/llvm-project/blob/033138ea452f5f493fb5095e5963419905ad12e1/clang/lib/CodeGen/CodeGenModule.cpp#L1048-L1050

5 files changed, 37 insertions, 44 deletions

diff --git a/compiler/rustc_codegen_llvm/src/base.rs b/compiler/rustc_codegen_llvm/src/base.rs
index b296db64ee9..893c909b204 100644
--- a/compiler/rustc_codegen_llvm/src/base.rs
+++ b/compiler/rustc_codegen_llvm/src/base.rs
@@ -218,27 +218,3 @@ pub fn visibility_to_llvm(linkage: Visibility) -> llvm::Visibility {
         Visibility::Protected => llvm::Visibility::Protected,
     }
 }
-
-pub fn linkage_from_llvm(linkage: llvm::Linkage) -> Linkage {
-    match linkage {
-        llvm::Linkage::ExternalLinkage => Linkage::External,
-        llvm::Linkage::AvailableExternallyLinkage => Linkage::AvailableExternally,
-        llvm::Linkage::LinkOnceAnyLinkage => Linkage::LinkOnceAny,
-        llvm::Linkage::LinkOnceODRLinkage => Linkage::LinkOnceODR,
-        llvm::Linkage::WeakAnyLinkage => Linkage::WeakAny,
-        llvm::Linkage::WeakODRLinkage => Linkage::WeakODR,
-        llvm::Linkage::AppendingLinkage => Linkage::Appending,
-        llvm::Linkage::InternalLinkage => Linkage::Internal,
-        llvm::Linkage::PrivateLinkage => Linkage::Private,
-        llvm::Linkage::ExternalWeakLinkage => Linkage::ExternalWeak,
-        llvm::Linkage::CommonLinkage => Linkage::Common,
-    }
-}
-
-pub fn visibility_from_llvm(linkage: llvm::Visibility) -> Visibility {
-    match linkage {
-        llvm::Visibility::Default => Visibility::Default,
-        llvm::Visibility::Hidden => Visibility::Hidden,
-        llvm::Visibility::Protected => Visibility::Protected,
-    }
-}
diff --git a/compiler/rustc_codegen_llvm/src/callee.rs b/compiler/rustc_codegen_llvm/src/callee.rs
index b26969a5012..bb16c90cd12 100644
--- a/compiler/rustc_codegen_llvm/src/callee.rs
+++ b/compiler/rustc_codegen_llvm/src/callee.rs
@@ -14,7 +14,6 @@ use tracing::debug;
 
 use rustc_middle::ty::layout::{FnAbiExt, HasTyCtxt};
 use rustc_middle::ty::{self, Instance, TypeFoldable};
-use rustc_target::spec::RelocModel;
 
 /// Codegens a reference to a fn/method item, monomorphizing and
 /// inlining as it goes.
@@ -181,7 +180,7 @@ pub fn get_fn(cx: &CodegenCx<'ll, 'tcx>, instance: Instance<'tcx>) -> &'ll Value
                 llvm::LLVMSetDLLStorageClass(llfn, llvm::DLLStorageClass::DllImport);
             }
 
-            if cx.tcx.sess.relocation_model() == RelocModel::Static {
+            if cx.should_assume_dso_local(llfn, true) {
                 llvm::LLVMRustSetDSOLocal(llfn, true);
             }
         }
diff --git a/compiler/rustc_codegen_llvm/src/consts.rs b/compiler/rustc_codegen_llvm/src/consts.rs
index 245842df1b0..e50d5506e22 100644
--- a/compiler/rustc_codegen_llvm/src/consts.rs
+++ b/compiler/rustc_codegen_llvm/src/consts.rs
@@ -17,7 +17,6 @@ use rustc_middle::mir::mono::MonoItem;
 use rustc_middle::ty::{self, Instance, Ty};
 use rustc_middle::{bug, span_bug};
 use rustc_target::abi::{AddressSpace, Align, HasDataLayout, LayoutOf, Primitive, Scalar, Size};
-use rustc_target::spec::RelocModel;
 use tracing::debug;
 
 pub fn const_alloc_to_llvm(cx: &CodegenCx<'ll, '_>, alloc: &Allocation) -> &'ll Value {
@@ -283,8 +282,8 @@ impl CodegenCx<'ll, 'tcx> {
             }
         }
 
-        if self.tcx.sess.relocation_model() == RelocModel::Static {
-            unsafe {
+        unsafe {
+            if self.should_assume_dso_local(g, true) {
                 llvm::LLVMRustSetDSOLocal(g, true);
             }
         }
@@ -370,9 +369,7 @@ impl StaticMethods for CodegenCx<'ll, 'tcx> {
             set_global_alignment(&self, g, self.align_of(ty));
             llvm::LLVMSetInitializer(g, v);
 
-            let linkage = base::linkage_from_llvm(llvm::LLVMRustGetLinkage(g));
-            let visibility = base::visibility_from_llvm(llvm::LLVMRustGetVisibility(g));
-            if self.should_assume_dso_local(linkage, visibility) {
+            if self.should_assume_dso_local(g, true) {
                 llvm::LLVMRustSetDSOLocal(g, true);
             }
 
diff --git a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
index 966be4a53fd..8b1dcea3fa2 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
@@ -72,7 +72,7 @@ pub enum Linkage {
 
 // LLVMRustVisibility
 #[repr(C)]
-#[derive(Copy, Clone)]
+#[derive(Copy, Clone, PartialEq)]
 pub enum Visibility {
     Default = 0,
     Hidden = 1,
@@ -1035,6 +1035,7 @@ extern "C" {
     pub fn LLVMDeleteGlobal(GlobalVar: &Value);
     pub fn LLVMGetInitializer(GlobalVar: &Value) -> Option<&Value>;
     pub fn LLVMSetInitializer(GlobalVar: &'a Value, ConstantVal: &'a Value);
+    pub fn LLVMIsThreadLocal(GlobalVar: &Value) -> Bool;
     pub fn LLVMSetThreadLocal(GlobalVar: &Value, IsThreadLocal: Bool);
     pub fn LLVMSetThreadLocalMode(GlobalVar: &Value, Mode: ThreadLocalMode);
     pub fn LLVMIsGlobalConstant(GlobalVar: &Value) -> Bool;
diff --git a/compiler/rustc_codegen_llvm/src/mono_item.rs b/compiler/rustc_codegen_llvm/src/mono_item.rs
index fc1f364e9c6..93456443aa0 100644
--- a/compiler/rustc_codegen_llvm/src/mono_item.rs
+++ b/compiler/rustc_codegen_llvm/src/mono_item.rs
@@ -37,7 +37,7 @@ impl PreDefineMethods<'tcx> for CodegenCx<'ll, 'tcx> {
         unsafe {
             llvm::LLVMRustSetLinkage(g, base::linkage_to_llvm(linkage));
             llvm::LLVMRustSetVisibility(g, base::visibility_to_llvm(visibility));
-            if self.should_assume_dso_local(linkage, visibility) {
+            if self.should_assume_dso_local(g, false) {
                 llvm::LLVMRustSetDSOLocal(g, true);
             }
         }
@@ -85,7 +85,7 @@ impl PreDefineMethods<'tcx> for CodegenCx<'ll, 'tcx> {
         attributes::from_fn_attrs(self, lldecl, instance);
 
         unsafe {
-            if self.should_assume_dso_local(linkage, visibility) {
+            if self.should_assume_dso_local(lldecl, false) {
                 llvm::LLVMRustSetDSOLocal(lldecl, true);
             }
         }
@@ -95,28 +95,48 @@ impl PreDefineMethods<'tcx> for CodegenCx<'ll, 'tcx> {
 }
 
 impl CodegenCx<'ll, 'tcx> {
-    /// Whether a definition (NB: not declaration!) can be assumed to be local to a group of
+    /// Whether a definition or declaration can be assumed to be local to a group of
     /// libraries that form a single DSO or executable.
     pub(crate) unsafe fn should_assume_dso_local(
         &self,
-        linkage: Linkage,
-        visibility: Visibility,
+        llval: &llvm::Value,
+        is_declaration: bool,
     ) -> bool {
-        if matches!(linkage, Linkage::Internal | Linkage::Private) {
+        let linkage = llvm::LLVMRustGetLinkage(llval);
+        let visibility = llvm::LLVMRustGetVisibility(llval);
+
+        if matches!(linkage, llvm::Linkage::InternalLinkage | llvm::Linkage::PrivateLinkage) {
             return true;
         }
 
-        if visibility != Visibility::Default && linkage != Linkage::ExternalWeak {
+        if visibility != llvm::Visibility::Default && linkage != llvm::Linkage::ExternalWeakLinkage
+        {
             return true;
         }
 
-        // Static relocation model should force copy relocations everywhere.
-        if self.tcx.sess.relocation_model() == RelocModel::Static {
+        // Symbols from executables can't really be imported any further.
+        let all_exe = self.tcx.sess.crate_types().iter().all(|ty| *ty == CrateType::Executable);
+        let is_declaration_for_linker =
+            is_declaration || linkage == llvm::Linkage::AvailableExternallyLinkage;
+        if all_exe && !is_declaration_for_linker {
             return true;
         }
 
-        // Symbols from executables can't really be imported any further.
-        if self.tcx.sess.crate_types().iter().all(|ty| *ty == CrateType::Executable) {
+        // PowerPC64 prefers TOC indirection to avoid copy relocations.
+        if matches!(&*self.tcx.sess.target.arch, "powerpc64" | "powerpc64le") {
+            return false;
+        }
+
+        // Thread-local variables generally don't support copy relocations.
+        let is_thread_local_var = llvm::LLVMIsAGlobalVariable(llval)
+            .map(|v| llvm::LLVMIsThreadLocal(v) == llvm::True)
+            .unwrap_or(false);
+        if is_thread_local_var {
+            return false;
+        }
+
+        // Static relocation model should force copy relocations everywhere.
+        if self.tcx.sess.relocation_model() == RelocModel::Static {
             return true;
         }