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Added comments on remapping expression IDs, and URL to spanviews

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This commit is contained in:
Rich Kadel 2020-10-25 01:53:44 -07:00
parent 198ba3bd1c
commit 5545c56e9d
111 changed files with 1189 additions and 118 deletions
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20
compiler/rustc_codegen_ssa/src/coverageinfo/map.rs
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@ -157,7 +157,25 @@ impl<'tcx> FunctionCoverage<'tcx> {
let mut counter_expressions = Vec::with_capacity(self.expressions.len());
let mut expression_regions = Vec::with_capacity(self.expressions.len());
let mut new_indexes = IndexVec::from_elem_n(None, self.expressions.len());
// Note that an `Expression`s at any given index can include other expressions as
// This closure converts any `Expression` operand (`lhs` or `rhs` of the `Op::Add` or
// `Op::Subtract` operation) into its native `llvm::coverage::Counter::CounterKind` type
// and value. Operand ID value `0` maps to `CounterKind::Zero`; values in the known range
// of injected LLVM counters map to `CounterKind::CounterValueReference` (and the value
// matches the injected counter index); and any other value is converted into a
// `CounterKind::Expression` with the expression's `new_index`.
//
// Expressions will be returned from this function in a sequential vector (array) of
// `CounterExpression`, so the expression IDs must be mapped from their original,
// potentially sparse set of indexes, originally in reverse order from `u32::MAX`.
//
// An `Expression` as an operand will have already been encountered as an `Expression` with
// operands, so its new_index will already have been generated (as a 1-up index value).
// (If an `Expression` as an operand does not have a corresponding new_index, it was
// probably optimized out, after the expression was injected into the MIR, so it will
// get a `CounterKind::Zero` instead.)
//
// In other words, an `Expression`s at any given index can include other expressions as
// operands, but expression operands can only come from the subset of expressions having
// `expression_index`s lower than the referencing `Expression`. Therefore, it is
// reasonable to look up the new index of an expression operand while the `new_indexes`