Auto merge of #102424 - sunfishcode:sunfishcode/hidden-main, r=nagisa

Declare `main` as visibility hidden on targets that default to hidden.

On targets with `default_hidden_visibility` set, which is currrently just WebAssembly, declare the generated `main` function with visibility hidden. This makes it consistent with clang's WebAssembly target, where `main` is just a user function that gets the same visibility as any other user function, which is hidden on WebAssembly unless explicitly overridden.

This will help simplify use cases which in the future may want to automatically wasm-export all visibility-"default" symbols. `main` isn't intended to be wasm-exported, and marking it hidden prevents it from being wasm-exported in that scenario.

1 files changed, 11 insertions, 1 deletions

diff --git a/compiler/rustc_codegen_llvm/src/declare.rs b/compiler/rustc_codegen_llvm/src/declare.rs
index 0f663a26732..f79ef11720d 100644
--- a/compiler/rustc_codegen_llvm/src/declare.rs
+++ b/compiler/rustc_codegen_llvm/src/declare.rs
@@ -32,6 +32,7 @@ fn declare_raw_fn<'ll>(
     name: &str,
     callconv: llvm::CallConv,
     unnamed: llvm::UnnamedAddr,
+    visibility: llvm::Visibility,
     ty: &'ll Type,
 ) -> &'ll Value {
     debug!("declare_raw_fn(name={:?}, ty={:?})", name, ty);
@@ -41,6 +42,7 @@ fn declare_raw_fn<'ll>(
 
     llvm::SetFunctionCallConv(llfn, callconv);
     llvm::SetUnnamedAddress(llfn, unnamed);
+    llvm::set_visibility(llfn, visibility);
 
     let mut attrs = SmallVec::<[_; 4]>::new();
 
@@ -78,7 +80,14 @@ impl<'ll, 'tcx> CodegenCx<'ll, 'tcx> {
         unnamed: llvm::UnnamedAddr,
         fn_type: &'ll Type,
     ) -> &'ll Value {
-        declare_raw_fn(self, name, llvm::CCallConv, unnamed, fn_type)
+        // Declare C ABI functions with the visibility used by C by default.
+        let visibility = if self.tcx.sess.target.default_hidden_visibility {
+            llvm::Visibility::Hidden
+        } else {
+            llvm::Visibility::Default
+        };
+
+        declare_raw_fn(self, name, llvm::CCallConv, unnamed, visibility, fn_type)
     }
 
     /// Declare a Rust function.
@@ -95,6 +104,7 @@ impl<'ll, 'tcx> CodegenCx<'ll, 'tcx> {
             name,
             fn_abi.llvm_cconv(),
             llvm::UnnamedAddr::Global,
+            llvm::Visibility::Default,
             fn_abi.llvm_type(self),
         );
         fn_abi.apply_attrs_llfn(self, llfn);