Auto merge of #79109 - richkadel:llvm-coverage-counters-2.0.5, r=tmandry

Coverage tests for remaining TerminatorKinds and async, improve Assert

Tested and validate results for panic unwind, panic abort, assert!()
macro, TerminatorKind::Assert (for example, numeric overflow), and
async/await.

Implemented a previous documented idea to change Assert handling to be
the same as FalseUnwind and Goto, so it doesn't get its own
BasicCoverageBlock anymore. This changed a couple of coverage regions,
but I validated those changes are not any worse than the prior results,
and probably help assure some consistency (even if some people might
disagree with how the code region is consistently computed).

Fixed issue with async/await. AggregateKind::Generator needs to be
handled like AggregateKind::Closure; coverage span for the outer async
function should not "cover" the async body, which is actually executed
in a separate "closure" MIR.

1 files changed, 12 insertions, 10 deletions

diff --git a/compiler/rustc_mir/src/transform/coverage/graph.rs b/compiler/rustc_mir/src/transform/coverage/graph.rs
index 9d375633dcf..f79f0d32538 100644
--- a/compiler/rustc_mir/src/transform/coverage/graph.rs
+++ b/compiler/rustc_mir/src/transform/coverage/graph.rs
@@ -118,18 +118,8 @@ impl CoverageGraph {
 
             match term.kind {
                 TerminatorKind::Return { .. }
-                // FIXME(richkadel): Add test(s) for `Abort` coverage.
                 | TerminatorKind::Abort
-                // FIXME(richkadel): Add test(s) for `Assert` coverage.
-                // Should `Assert` be handled like `FalseUnwind` instead? Since we filter out unwind
-                // branches when creating the BCB CFG, aren't `Assert`s (without unwinds) just like
-                // `FalseUnwinds` (which are kind of like `Goto`s)?
-                | TerminatorKind::Assert { .. }
-                // FIXME(richkadel): Add test(s) for `Yield` coverage, and confirm coverage is
-                // sensible for code using the `yield` keyword.
                 | TerminatorKind::Yield { .. }
-                // FIXME(richkadel): Also add coverage tests using async/await, and threading.
-
                 | TerminatorKind::SwitchInt { .. } => {
                     // The `bb` has more than one _outgoing_ edge, or exits the function. Save the
                     // current sequence of `basic_blocks` gathered to this point, as a new
@@ -147,6 +137,16 @@ impl CoverageGraph {
                     // `Terminator`s `successors()` list) checking the number of successors won't
                     // work.
                 }
+
+                // The following `TerminatorKind`s are either not expected outside an unwind branch,
+                // or they should not (under normal circumstances) branch. Coverage graphs are
+                // simplified by assuring coverage results are accurate for program executions that
+                // don't panic.
+                //
+                // Programs that panic and unwind may record slightly inaccurate coverage results
+                // for a coverage region containing the `Terminator` that began the panic. This
+                // is as intended. (See Issue #78544 for a possible future option to support
+                // coverage in test programs that panic.)
                 TerminatorKind::Goto { .. }
                 | TerminatorKind::Resume
                 | TerminatorKind::Unreachable
@@ -154,6 +154,7 @@ impl CoverageGraph {
                 | TerminatorKind::DropAndReplace { .. }
                 | TerminatorKind::Call { .. }
                 | TerminatorKind::GeneratorDrop
+                | TerminatorKind::Assert { .. }
                 | TerminatorKind::FalseEdge { .. }
                 | TerminatorKind::FalseUnwind { .. }
                 | TerminatorKind::InlineAsm { .. } => {}
@@ -278,6 +279,7 @@ rustc_index::newtype_index! {
     /// A node in the [control-flow graph][CFG] of CoverageGraph.
     pub(super) struct BasicCoverageBlock {
         DEBUG_FORMAT = "bcb{}",
+        const START_BCB = 0,
     }
 }