Prevent frontend function confusion (#383)

Function symbols can clash as we compile multiple YUL `object`
definition into the same `LLVM` module.
- Disambiguate via unique function symbols based its location (runtime
or deploy code).
- Use `LinkOnceODR` linkage for compiler builtin helpers.

---------

Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>

crates/llvm-context/src/polkavm/context/runtime.rs

@@ -30,8 +30,9 @@ pub trait RuntimeFunction {
             Self::NAME,
             Self::r#type(context),
             0,
-            Some(inkwell::module::Linkage::External), // TODO: `Private` emits unrelocated AUIPC?
+            Some(inkwell::module::Linkage::LinkOnceODR),
             None,
+            false,
         )?;
 
         let mut attributes = Self::ATTRIBUTES.to_vec();
@@ -45,6 +46,12 @@ pub trait RuntimeFunction {
             &attributes,
             true,
         );
+        let function = function.borrow().declaration().function_value();
+        let comdat = context
+            .module()
+            .get_or_insert_comdat(&format!("{}_comdat", Self::NAME));
+        comdat.set_selection_kind(inkwell::comdat::ComdatSelectionKind::NoDuplicates);
+        function.as_global_value().set_comdat(comdat);
 
         Ok(())
     }
@@ -52,7 +59,7 @@ pub trait RuntimeFunction {
     /// Get the function declaration.
     fn declaration<'ctx>(context: &Context<'ctx>) -> Declaration<'ctx> {
         context
-            .get_function(Self::NAME)
+            .get_function(Self::NAME, false)
             .unwrap_or_else(|| panic!("runtime function {} should be declared", Self::NAME))
             .borrow()
             .declaration()
@@ -60,7 +67,7 @@ pub trait RuntimeFunction {
 
     /// Emit the function.
     fn emit(&self, context: &mut Context) -> anyhow::Result<()> {
-        context.set_current_function(Self::NAME, None)?;
+        context.set_current_function(Self::NAME, None, false)?;
         context.set_basic_block(context.current_function().borrow().entry_block());
 
         let return_value = self.emit_body(context)?;
@@ -99,7 +106,7 @@ pub trait RuntimeFunction {
     ) -> inkwell::values::BasicValueEnum<'ctx> {
         let name = Self::NAME;
         context
-            .get_function(name)
+            .get_function(name, false)
             .unwrap_or_else(|| panic!("runtime function {name} should be declared"))
             .borrow()
             .declaration()