33/// This pass demotes 'by-value' function return types to 'by-reference` pointer types, based on
44/// target specific parameters.
55///
6- /// An extra argument pointer is added to the function and this pointer is also returned. The
7- /// return value is mem_copied to the new argument instead of being returned by value.
6+ /// An extra argument pointer is added to the function.
7+ /// The return value is mem_copied to the new argument instead of being returned by value.
88use crate :: {
9- AnalysisResults , BlockArgument , Context , Function , InstOp , Instruction , InstructionInserter ,
10- IrError , Module , Pass , PassMutability , ScopedPass , Type , Value ,
9+ AnalysisResults , BlockArgument , ConstantContent , Context , Function , InstOp , Instruction ,
10+ InstructionInserter , IrError , Module , Pass , PassMutability , ScopedPass , Type , Value ,
1111} ;
1212
1313pub const RET_DEMOTION_NAME : & str = "ret-demotion" ;
@@ -23,7 +23,7 @@ pub fn create_ret_demotion_pass() -> Pass {
2323
2424pub fn ret_val_demotion (
2525 context : & mut Context ,
26- _ : & AnalysisResults ,
26+ _analyses : & AnalysisResults ,
2727 module : Module ,
2828) -> Result < bool , IrError > {
2929 // This is a module pass because we need to update all the callers of a function if we change
@@ -39,14 +39,18 @@ pub fn ret_val_demotion(
3939
4040 changed = true ;
4141
42- // Change the function signature. It now returns a pointer.
42+ // Change the function signature.
4343 let ptr_ret_type = Type :: new_typed_pointer ( context, ret_type) ;
44- function . set_return_type ( context, ptr_ret_type ) ;
44+ let unit_ty = Type :: get_unit ( context) ;
4545
4646 // The storage for the return value must be determined. For entry-point functions it's a new
4747 // local and otherwise it's an extra argument.
4848 let entry_block = function. get_entry_block ( context) ;
4949 let ptr_arg_val = if function. is_entry ( context) {
50+ // Entry functions return a pointer to the original return type.
51+ function. set_return_type ( context, ptr_ret_type) ;
52+
53+ // Create a local variable to hold the return value.
5054 let ret_var = function. new_unique_local_var (
5155 context,
5256 "__ret_value" . to_owned ( ) ,
@@ -61,6 +65,9 @@ pub fn ret_val_demotion(
6165 entry_block. prepend_instructions ( context, vec ! [ get_ret_var] ) ;
6266 get_ret_var
6367 } else {
68+ // non-entry functions now return unit.
69+ function. set_return_type ( context, unit_ty) ;
70+
6471 let ptr_arg_val = Value :: new_argument (
6572 context,
6673 BlockArgument {
@@ -102,10 +109,20 @@ pub fn ret_val_demotion(
102109 . append ( context)
103110 . store ( ptr_arg_val, ret_val)
104111 . add_metadatum ( context, md_idx) ;
105- ret_block
106- . append ( context)
107- . ret ( ptr_arg_val, ptr_ret_type)
108- . add_metadatum ( context, md_idx) ;
112+
113+ if !function. is_entry ( context) {
114+ let unit_ret = ConstantContent :: get_unit ( context) ;
115+ ret_block
116+ . append ( context)
117+ . ret ( unit_ret, unit_ty)
118+ . add_metadatum ( context, md_idx) ;
119+ } else {
120+ // Entry functions still return the pointer to the return value.
121+ ret_block
122+ . append ( context)
123+ . ret ( ptr_arg_val, ptr_ret_type)
124+ . add_metadatum ( context, md_idx) ;
125+ }
109126 }
110127
111128 // If the function isn't an entry point we need to update all the callers to pass the extra
@@ -180,7 +197,7 @@ fn update_callers(context: &mut Context, function: Function, ret_type: Type) {
180197 Value :: new_instruction ( context, calling_block, InstOp :: Call ( function, new_args) ) ;
181198
182199 // And finally load the value from the new local var.
183- let load_val = Value :: new_instruction ( context, calling_block, InstOp :: Load ( new_call_val ) ) ;
200+ let load_val = Value :: new_instruction ( context, calling_block, InstOp :: Load ( get_loc_val ) ) ;
184201
185202 calling_block
186203 . replace_instruction ( context, call_val, get_loc_val, false )
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