diff options
Diffstat (limited to 'compiler/rustc_mir_transform/src/coverage/graph.rs')
| -rw-r--r-- | compiler/rustc_mir_transform/src/coverage/graph.rs | 29 |
1 files changed, 7 insertions, 22 deletions
diff --git a/compiler/rustc_mir_transform/src/coverage/graph.rs b/compiler/rustc_mir_transform/src/coverage/graph.rs index 986d2fd190d..ea1223fbca6 100644 --- a/compiler/rustc_mir_transform/src/coverage/graph.rs +++ b/compiler/rustc_mir_transform/src/coverage/graph.rs @@ -9,6 +9,7 @@ use rustc_index::{IndexSlice, IndexVec}; use rustc_middle::mir::coverage::*; use rustc_middle::mir::{self, BasicBlock, BasicBlockData, Terminator, TerminatorKind}; +use std::cmp::Ordering; use std::ops::{Index, IndexMut}; const ID_SEPARATOR: &str = ","; @@ -212,8 +213,12 @@ impl CoverageGraph { } #[inline(always)] - pub fn dominators(&self) -> &Dominators<BasicCoverageBlock> { - self.dominators.as_ref().unwrap() + pub fn rank_partial_cmp( + &self, + a: BasicCoverageBlock, + b: BasicCoverageBlock, + ) -> Option<Ordering> { + self.dominators.as_ref().unwrap().rank_partial_cmp(a, b) } } @@ -650,26 +655,6 @@ pub(super) fn find_loop_backedges( let mut backedges = IndexVec::from_elem_n(Vec::<BasicCoverageBlock>::new(), num_bcbs); // Identify loops by their backedges. - // - // The computational complexity is bounded by: n(s) x d where `n` is the number of - // `BasicCoverageBlock` nodes (the simplified/reduced representation of the CFG derived from the - // MIR); `s` is the average number of successors per node (which is most likely less than 2, and - // independent of the size of the function, so it can be treated as a constant); - // and `d` is the average number of dominators per node. - // - // The average number of dominators depends on the size and complexity of the function, and - // nodes near the start of the function's control flow graph typically have less dominators - // than nodes near the end of the CFG. Without doing a detailed mathematical analysis, I - // think the resulting complexity has the characteristics of O(n log n). - // - // The overall complexity appears to be comparable to many other MIR transform algorithms, and I - // don't expect that this function is creating a performance hot spot, but if this becomes an - // issue, there may be ways to optimize the `dominates` algorithm (as indicated by an - // existing `FIXME` comment in that code), or possibly ways to optimize it's usage here, perhaps - // by keeping track of results for visited `BasicCoverageBlock`s if they can be used to short - // circuit downstream `dominates` checks. - // - // For now, that kind of optimization seems unnecessarily complicated. for (bcb, _) in basic_coverage_blocks.iter_enumerated() { for &successor in &basic_coverage_blocks.successors[bcb] { if basic_coverage_blocks.dominates(successor, bcb) { |