11use std:: collections:: VecDeque ;
22
33use rustc_data_structures:: fx:: FxIndexMap ;
4+ use rustc_index:: IndexVec ;
45use rustc_middle:: bug;
56use rustc_middle:: mir:: coverage:: {
67 BlockMarkerId , ConditionId , ConditionInfo , DecisionId , MCDCBranchMarkers , MCDCBranchSpan ,
@@ -14,10 +15,9 @@ use rustc_span::Span;
1415use crate :: build:: Builder ;
1516use crate :: errors:: { MCDCExceedsConditionLimit , MCDCExceedsDecisionDepth } ;
1617
17- /// The MCDC bitmap scales exponentially (2^n) based on the number of conditions seen,
18- /// So llvm sets a maximum value prevents the bitmap footprint from growing too large without the user's knowledge.
19- /// This limit may be relaxed if the [upstream change](https://github.com/llvm/llvm-project/pull/82448) is merged.
20- const MAX_CONDITIONS_IN_DECISION : usize = 6 ;
18+ /// LLVM uses `i16` to represent condition id. Hence `i16::MAX` is the hard limit for number of
19+ /// conditions in a decision.
20+ const MAX_CONDITIONS_IN_DECISION : usize = i16:: MAX as usize ;
2121
2222/// MCDC allocates an i32 variable on stack for each depth. Ignore decisions nested too much to prevent it
2323/// consuming excessive memory.
@@ -41,6 +41,7 @@ impl BooleanDecisionCtx {
4141 span : Span :: default ( ) ,
4242 end_markers : vec ! [ ] ,
4343 decision_depth : 0 ,
44+ num_test_vectors : 0 ,
4445 } ,
4546 decision_stack : VecDeque :: new ( ) ,
4647 conditions : vec ! [ ] ,
@@ -158,11 +159,11 @@ impl BooleanDecisionCtx {
158159 self . decision_info . end_markers . push ( false_marker) ;
159160 }
160161
161- self . conditions . push ( MCDCBranchSpan {
162+ self . conditions . push ( MCDCBranchSpan :: new (
162163 span,
163164 condition_info,
164- markers : MCDCBranchMarkers :: Boolean ( true_marker, false_marker) ,
165- } ) ;
165+ MCDCBranchMarkers :: Boolean ( true_marker, false_marker) ,
166+ ) ) ;
166167 }
167168
168169 fn is_finished ( & self ) -> bool {
@@ -257,9 +258,86 @@ struct MCDCTargetInfo {
257258}
258259
259260impl MCDCTargetInfo {
261+ fn new ( decision : MCDCDecisionSpan , conditions : Vec < MCDCBranchSpan > ) -> Self {
262+ let mut this = Self { decision, conditions, nested_decisions_id : vec ! [ ] } ;
263+ this. calc_test_vectors_index ( ) ;
264+ this
265+ }
266+
260267 fn set_depth ( & mut self , depth : u16 ) {
261268 self . decision . decision_depth = depth;
262269 }
270+
271+ // LLVM checks the executed test vector by accumulate indices of tested branches.
272+ // We calculate number of all possible test vectors of the decision and assign indices
273+ // for each branch here.
274+ // See https://discourse.llvm.org/t/rfc-coverage-new-algorithm-and-file-format-for-mc-dc/76798/ for
275+ // more details of the algorithm.
276+ // The process of this function is mostly like `TVIdxBuilder` at
277+ // https://github.com/llvm/llvm-project/blob/d594d9f7f4dc6eb748b3261917db689fdc348b96/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp#L226
278+ fn calc_test_vectors_index ( & mut self ) {
279+ let Self { decision, conditions, .. } = self ;
280+ let mut indegree_stats = IndexVec :: < ConditionId , usize > :: from_elem_n ( 0 , conditions. len ( ) ) ;
281+ // `num_paths` is `width` described at the llvm RFC, which indicates how many paths reaching the condition.
282+ let mut num_paths_stats = IndexVec :: < ConditionId , usize > :: from_elem_n ( 0 , conditions. len ( ) ) ;
283+ let mut next_conditions = conditions
284+ . iter_mut ( )
285+ . map ( |branch| {
286+ let ConditionInfo { condition_id, true_next_id, false_next_id } =
287+ branch. condition_info ;
288+ [ true_next_id, false_next_id]
289+ . into_iter ( )
290+ . filter_map ( std:: convert:: identity)
291+ . for_each ( |next_id| indegree_stats[ next_id] += 1 ) ;
292+ ( condition_id, branch)
293+ } )
294+ . collect :: < FxIndexMap < _ , _ > > ( ) ;
295+
296+ let mut queue =
297+ VecDeque :: from_iter ( next_conditions. swap_remove ( & ConditionId :: START ) . into_iter ( ) ) ;
298+ num_paths_stats[ ConditionId :: START ] = 1 ;
299+ let mut decision_end_nodes = Vec :: new ( ) ;
300+ while let Some ( branch) = queue. pop_front ( ) {
301+ let MCDCBranchSpan {
302+ span : _,
303+ condition_info : ConditionInfo { condition_id, true_next_id, false_next_id } ,
304+ markers : _,
305+ false_index,
306+ true_index,
307+ } = branch;
308+ let this_paths_count = num_paths_stats[ * condition_id] ;
309+ for ( next, index) in [ ( false_next_id, false_index) , ( true_next_id, true_index) ] {
310+ if let Some ( next_id) = next {
311+ let next_paths_count = & mut num_paths_stats[ * next_id] ;
312+ * index = * next_paths_count;
313+ * next_paths_count = next_paths_count. saturating_add ( this_paths_count) ;
314+ let next_indegree = & mut indegree_stats[ * next_id] ;
315+ * next_indegree -= 1 ;
316+ if * next_indegree == 0 {
317+ queue. push_back ( next_conditions. swap_remove ( next_id) . expect (
318+ "conditions with non-zero indegree before must be in next_conditions" ,
319+ ) ) ;
320+ }
321+ } else {
322+ decision_end_nodes. push ( ( this_paths_count, * condition_id, index) ) ;
323+ }
324+ }
325+ }
326+ assert ! ( next_conditions. is_empty( ) , "the decision tree has untouched nodes" ) ;
327+ let mut cur_idx = 0 ;
328+ // LLVM hopes the end nodes is sorted in ascending order by `num_paths`.
329+ decision_end_nodes. sort_by_key ( |( num_paths, _, _) | usize:: MAX - * num_paths) ;
330+ for ( num_paths, condition_id, index) in decision_end_nodes {
331+ assert_eq ! (
332+ num_paths, num_paths_stats[ condition_id] ,
333+ "end nodes should not be updated since they were visited"
334+ ) ;
335+ assert_eq ! ( * index, usize :: MAX , "end nodes should not be assigned index before" ) ;
336+ * index = cur_idx;
337+ cur_idx += num_paths;
338+ }
339+ decision. num_test_vectors = cur_idx;
340+ }
263341}
264342
265343#[ derive( Default ) ]
@@ -323,7 +401,7 @@ impl MCDCInfoBuilder {
323401 }
324402 // Ignore decisions with only one condition given that mcdc for them is completely equivalent to branch coverage.
325403 2 ..=MAX_CONDITIONS_IN_DECISION => {
326- let info = MCDCTargetInfo { decision, conditions, nested_decisions_id : vec ! [ ] } ;
404+ let info = MCDCTargetInfo :: new ( decision, conditions) ;
327405 Some ( self . mcdc_targets . entry ( id) . or_insert ( info) )
328406 }
329407 _ => {
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