Add comments about address spaces

1 files changed, 13 insertions, 0 deletions

diff --git a/compiler/rustc_codegen_llvm/src/consts.rs b/compiler/rustc_codegen_llvm/src/consts.rs
index b88fd133e8e..771ebf2057f 100644
--- a/compiler/rustc_codegen_llvm/src/consts.rs
+++ b/compiler/rustc_codegen_llvm/src/consts.rs
@@ -214,6 +214,10 @@ impl<'ll> CodegenCx<'ll, '_> {
         unsafe { llvm::LLVMConstPointerCast(val, ty) }
     }
 
+    /// Create a global variable.
+    ///
+    /// The returned global variable is a pointer in the default address space for globals.
+    /// Fails if a symbol with the given name already exists.
     pub(crate) fn static_addr_of_mut(
         &self,
         cv: &'ll Value,
@@ -237,6 +241,9 @@ impl<'ll> CodegenCx<'ll, '_> {
         gv
     }
 
+    /// Create a global constant.
+    ///
+    /// The returned global variable is a pointer in the default address space for globals.
     pub(crate) fn static_addr_of_impl(
         &self,
         cv: &'ll Value,
@@ -534,8 +541,14 @@ impl<'ll> CodegenCx<'ll, '_> {
 }
 
 impl<'ll> StaticCodegenMethods for CodegenCx<'ll, '_> {
+    /// Get a pointer to a global variable.
+    ///
+    /// The pointer will always be in the default address space. If global variables default to a
+    /// different address space, an addrspacecast is inserted.
     fn static_addr_of(&self, cv: &'ll Value, align: Align, kind: Option<&str>) -> &'ll Value {
         let gv = self.static_addr_of_impl(cv, align, kind);
+        // static_addr_of_impl returns the bare global variable, which might not be in the default
+        // address space. Cast to the default address space if necessary.
         self.const_pointercast(gv, self.type_ptr())
     }