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.

5 files changed, 46 insertions, 9 deletions

diff --git a/compiler/rustc_codegen_llvm/src/builder.rs b/compiler/rustc_codegen_llvm/src/builder.rs
index 59b1c7fb5db..a6cd1059dc7 100644
--- a/compiler/rustc_codegen_llvm/src/builder.rs
+++ b/compiler/rustc_codegen_llvm/src/builder.rs
@@ -1458,7 +1458,12 @@ impl<'a, 'll, 'tcx> Builder<'a, 'll, 'tcx> {
         } else {
             format!("llvm.{}.sat.i{}.f{}", instr, int_width, float_width)
         };
-        let f = self.declare_cfn(&name, llvm::UnnamedAddr::No, self.type_func(&[src_ty], dest_ty));
+        let f = self.declare_cfn(
+            &name,
+            llvm::UnnamedAddr::No,
+            llvm::Visibility::Default,
+            self.type_func(&[src_ty], dest_ty),
+        );
         self.call(self.type_func(&[src_ty], dest_ty), f, &[val], None)
     }
 
diff --git a/compiler/rustc_codegen_llvm/src/context.rs b/compiler/rustc_codegen_llvm/src/context.rs
index 67ffc7cb951..6aeb56eb5ad 100644
--- a/compiler/rustc_codegen_llvm/src/context.rs
+++ b/compiler/rustc_codegen_llvm/src/context.rs
@@ -528,7 +528,12 @@ impl<'ll, 'tcx> MiscMethods<'tcx> for CodegenCx<'ll, 'tcx> {
                     llfn
                 } else {
                     let fty = self.type_variadic_func(&[], self.type_i32());
-                    let llfn = self.declare_cfn(name, llvm::UnnamedAddr::Global, fty);
+                    let llfn = self.declare_cfn(
+                        name,
+                        llvm::UnnamedAddr::Global,
+                        llvm::Visibility::Default,
+                        fty,
+                    );
                     let target_cpu = attributes::target_cpu_attr(self);
                     attributes::apply_to_llfn(llfn, llvm::AttributePlace::Function, &[target_cpu]);
                     llfn
@@ -585,7 +590,13 @@ impl<'ll, 'tcx> MiscMethods<'tcx> for CodegenCx<'ll, 'tcx> {
 
     fn declare_c_main(&self, fn_type: Self::Type) -> Option<Self::Function> {
         if self.get_declared_value("main").is_none() {
-            Some(self.declare_cfn("main", llvm::UnnamedAddr::Global, fn_type))
+            let visibility = if self.sess().target.default_hidden_visibility {
+                llvm::Visibility::Hidden
+            } else {
+                llvm::Visibility::Default
+            };
+
+            Some(self.declare_cfn("main", llvm::UnnamedAddr::Global, visibility, fn_type))
         } else {
             // If the symbol already exists, it is an error: for example, the user wrote
             // #[no_mangle] extern "C" fn main(..) {..}
@@ -615,7 +626,7 @@ impl<'ll> CodegenCx<'ll, '_> {
         } else {
             self.type_variadic_func(&[], ret)
         };
-        let f = self.declare_cfn(name, llvm::UnnamedAddr::No, fn_ty);
+        let f = self.declare_cfn(name, llvm::UnnamedAddr::No, llvm::Visibility::Default, fn_ty);
         self.intrinsics.borrow_mut().insert(name, (fn_ty, f));
         (fn_ty, f)
     }
diff --git a/compiler/rustc_codegen_llvm/src/declare.rs b/compiler/rustc_codegen_llvm/src/declare.rs
index 0f663a26732..21c466ddc24 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::SetVisibility(llfn, visibility);
 
     let mut attrs = SmallVec::<[_; 4]>::new();
 
@@ -76,9 +78,10 @@ impl<'ll, 'tcx> CodegenCx<'ll, 'tcx> {
         &self,
         name: &str,
         unnamed: llvm::UnnamedAddr,
+        visibility: llvm::Visibility,
         fn_type: &'ll Type,
     ) -> &'ll Value {
-        declare_raw_fn(self, name, llvm::CCallConv, unnamed, fn_type)
+        declare_raw_fn(self, name, llvm::CCallConv, unnamed, visibility, fn_type)
     }
 
     /// Declare a Rust function.
@@ -95,6 +98,7 @@ 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);
diff --git a/compiler/rustc_codegen_llvm/src/intrinsic.rs b/compiler/rustc_codegen_llvm/src/intrinsic.rs
index a640de42a6a..4e1e6371ad4 100644
--- a/compiler/rustc_codegen_llvm/src/intrinsic.rs
+++ b/compiler/rustc_codegen_llvm/src/intrinsic.rs
@@ -1216,7 +1216,7 @@ fn generic_simd_intrinsic<'ll, 'tcx>(
             _ => return_error!("unrecognized intrinsic `{}`", name),
         };
         let llvm_name = &format!("llvm.{0}.v{1}{2}", intr_name, in_len, elem_ty_str);
-        let f = bx.declare_cfn(llvm_name, llvm::UnnamedAddr::No, fn_ty);
+        let f = bx.declare_cfn(llvm_name, llvm::UnnamedAddr::No, llvm::Visibility::Default, fn_ty);
         let c =
             bx.call(fn_ty, f, &args.iter().map(|arg| arg.immediate()).collect::<Vec<_>>(), None);
         Ok(c)
@@ -1416,7 +1416,12 @@ fn generic_simd_intrinsic<'ll, 'tcx>(
             &[llvm_pointer_vec_ty, alignment_ty, mask_ty, llvm_elem_vec_ty],
             llvm_elem_vec_ty,
         );
-        let f = bx.declare_cfn(&llvm_intrinsic, llvm::UnnamedAddr::No, fn_ty);
+        let f = bx.declare_cfn(
+            &llvm_intrinsic,
+            llvm::UnnamedAddr::No,
+            llvm::Visibility::Default,
+            fn_ty,
+        );
         let v =
             bx.call(fn_ty, f, &[args[1].immediate(), alignment, mask, args[0].immediate()], None);
         return Ok(v);
@@ -1542,7 +1547,12 @@ fn generic_simd_intrinsic<'ll, 'tcx>(
             format!("llvm.masked.scatter.{}.{}", llvm_elem_vec_str, llvm_pointer_vec_str);
         let fn_ty =
             bx.type_func(&[llvm_elem_vec_ty, llvm_pointer_vec_ty, alignment_ty, mask_ty], ret_t);
-        let f = bx.declare_cfn(&llvm_intrinsic, llvm::UnnamedAddr::No, fn_ty);
+        let f = bx.declare_cfn(
+            &llvm_intrinsic,
+            llvm::UnnamedAddr::No,
+            llvm::Visibility::Default,
+            fn_ty,
+        );
         let v =
             bx.call(fn_ty, f, &[args[0].immediate(), args[1].immediate(), alignment, mask], None);
         return Ok(v);
@@ -1991,7 +2001,8 @@ unsupported {} from `{}` with element `{}` of size `{}` to `{}`"#,
         let vec_ty = bx.cx.type_vector(elem_ty, in_len as u64);
 
         let fn_ty = bx.type_func(&[vec_ty, vec_ty], vec_ty);
-        let f = bx.declare_cfn(llvm_intrinsic, llvm::UnnamedAddr::No, fn_ty);
+        let f =
+            bx.declare_cfn(llvm_intrinsic, llvm::UnnamedAddr::No, llvm::Visibility::Default, fn_ty);
         let v = bx.call(fn_ty, f, &[lhs, rhs], None);
         return Ok(v);
     }
diff --git a/compiler/rustc_codegen_llvm/src/llvm/mod.rs b/compiler/rustc_codegen_llvm/src/llvm/mod.rs
index 6602a4ab863..942e7e0427c 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/mod.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm/mod.rs
@@ -172,6 +172,12 @@ pub fn SetUnnamedAddress(global: &Value, unnamed: UnnamedAddr) {
     }
 }
 
+pub fn SetVisibility(global: &Value, visibility: Visibility) {
+    unsafe {
+        LLVMRustSetVisibility(global, visibility);
+    }
+}
+
 pub fn set_thread_local_mode(global: &Value, mode: ThreadLocalMode) {
     unsafe {
         LLVMSetThreadLocalMode(global, mode);