@@ -4,7 +4,7 @@ use crate::{
44} ;
55use rustc_middle:: mir:: * ;
66use rustc_middle:: ty:: { Ty , TyCtxt } ;
7- use std:: fmt:: Debug ;
7+ use std:: { borrow :: Cow , fmt:: Debug } ;
88
99use super :: simplify:: simplify_cfg;
1010
@@ -98,22 +98,67 @@ impl<'tcx> MirPass<'tcx> for EarlyOtherwiseBranch {
9898 StatementKind :: Assign ( box ( Place :: from ( not_equal_temp) , not_equal_rvalue) ) ,
9999 ) ;
100100
101- // switch on the NotEqual. If true, then jump to the `otherwise` case.
102- // If false, then jump to a basic block that then jumps to the correct disciminant case
101+ // Switch on the NotEqual. If true, then jump to the `otherwise` case,
102+ // since we know the discriminant values are not the same.
103103 let true_case = opt_to_apply. infos [ 0 ] . first_switch_info . otherwise_bb ;
104- let targets_second_switch =
105- & opt_to_apply. infos [ 0 ] . second_switch_info . targets_with_values ;
106- assert_eq ! (
107- 1 ,
108- targets_second_switch. len( ) ,
109- "We should only have one target besides the otherwise"
110- ) ;
111104
112- // Since we know that the two discriminant values are equal,
113- // we can jump directly to the target in the second switch
114- let false_case = targets_second_switch[ 0 ] . 0 ;
105+ // In the false case we know that the two discriminant values are equal,
106+ // however we still need to account for the following scenario:
107+ // ```rust
108+ // match (x, y) {
109+ // (Some(_), Some(_)) => 0,
110+ // _ => 2
111+ // }
112+ // ```
113+ //
114+ // Here, the two match arms have the same discriminant values, but
115+ // we need to make sure that we did not reach a `(None, None)` pattern.
116+ // We therefore construct a new basic block that can disambiguate where to go.
117+
118+ let mut targets_and_values_to_jump_to = vec ! [ ] ;
119+ for info in opt_to_apply. infos . iter ( ) {
120+ for ( _, value) in info. first_switch_info . targets_with_values . iter ( ) {
121+ // Find corresponding value in second switch info -
122+ // this is where we want to jump to
123+ if let Some ( ( target_to_jump_to, _) ) = info
124+ . second_switch_info
125+ . targets_with_values
126+ . iter ( )
127+ . find ( |( _, second_value) | value == second_value)
128+ {
129+ targets_and_values_to_jump_to. push ( ( target_to_jump_to, value) ) ;
130+ }
131+ }
132+ }
133+
134+ let ( mut targets_to_jump_to, values_to_jump_to) : ( Vec < _ > , Vec < _ > ) =
135+ targets_and_values_to_jump_to. iter ( ) . cloned ( ) . unzip ( ) ;
136+
137+ // add otherwise case in the end
138+ targets_to_jump_to. push ( opt_to_apply. infos [ 0 ] . first_switch_info . otherwise_bb ) ;
139+
140+ // new block that jumps to the correct discriminant case. This block is switched to if the discriminants are equal
141+ let mut new_switch_data = BasicBlockData :: new ( Some ( Terminator {
142+ source_info : opt_to_apply. infos [ 0 ] . second_switch_info . discr_source_info ,
143+ kind : TerminatorKind :: SwitchInt {
144+ // the first and second discriminants are equal, so just pick one
145+ discr : Operand :: Copy ( first_descriminant_place) ,
146+ switch_ty : discr_type,
147+ values : Cow :: from ( values_to_jump_to) ,
148+ targets : targets_to_jump_to,
149+ } ,
150+ } ) ) ;
151+
152+ let basic_block_first_switch = opt_to_apply. basic_block_first_switch ;
153+
154+ // Inherit the is_cleanup from the bb we are jumping from, which is where the first switch is
155+ new_switch_data. is_cleanup = body. basic_blocks ( ) [ basic_block_first_switch] . is_cleanup ;
156+
157+ let new_switch_bb = patch. new_block ( new_switch_data) ;
158+ let false_case = new_switch_bb;
159+
115160 patch. patch_terminator (
116- opt_to_apply . basic_block_first_switch ,
161+ basic_block_first_switch,
117162 TerminatorKind :: if_ (
118163 tcx,
119164 Operand :: Move ( Place :: from ( not_equal_temp) ) ,
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