WIP - Changes to try to fix and reland cover unreachable statements #85210
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Fixes: rust-lang#84018 With `-Z instrument-coverage`, coverage reporting of dead blocks (for example, blocks dropped because a conditional branch is dropped, based on const evaluation) is now supported. If `instrument-coverage` is enabled, `simplify::remove_dead_blocks()` finds all dropped coverage `Statement`s and adds their `code_region`s as `Unreachable` coverage `Statement`s to the `START_BLOCK`, so they are still included in the coverage map. Check out the resulting changes in the test coverage reports in this PR.
...by saving dead counters/expressions.
Unfortunately, I'm still getting the same result, when trying to get
coverage from Fuchsia apps (at least those using fuchsia_async, but that
may not be the specific cause):
When running `llvm-cov` to get the coverage report, I get the well known
and still useless message:
```
Failed to load coverage: Malformed instrumentation profile data
```
I can change CoverageMappingReader.cpp to avoid failing and I will see
some coverage results (maybe most of the coverage results) but there is
missing coverage as well. I don't know why the function name is not
found.
The "hack" is, change this:
```c++
if (Error Err = CFR->template getFuncName<Endian>(ProfileNames, FuncName))
return Err;
if (FuncName.empty())
return make_error<InstrProfError>(instrprof_error::malformed);
++CovMapNumUsedRecords;
```
to this:
```c++
if (Error Err = CFR->template getFuncName<Endian>(ProfileNames, FuncName))
return Err;
if (FuncName.empty())
FuncName = "MissingFuncNameForCoverage";
++CovMapNumUsedRecords;
```
I did learn that the original implementation (replacing counters and
expressions with Zero/unreachable counters), so this PR addresses that
issue. I hoped that it would fix the problem, but it didn't.
Specifically regarding the LLVM coverage adjustment (improvement?) made
in this version, compared to the reverted PR (rust-lang#84797):
LLVM requires all counters with code regions be added to the coverage
map. The original dead block fix replaced the counters and expressions
with a Zero (unreachable) code region. This commit saves the original
counter or expression, without adding a statement to increment the
counter for the eliminated dead block.
I ran into an error trying to fix dead block coverage and realized the `coverageinfo` query is getting a different MIR compared to the codegenned MIR, which can sometimes be a problem during mapgen. I changed that query to use the `InstandeDef` (which includes the generic parameter substitutions, prosibly specific to const params) instead of the `DefId` (without unknown/default const substitutions).
rust-highfive
added
the
S-waiting-on-review
Collaborator
|
☔ The latest upstream changes (presumably #85328) made this pull request unmergeable. Please resolve the merge conflicts. |
Contributor
Author
|
Abandoned in lieu of #85385 |
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WIP attempt to add coverage
0of dead blocks...by saving dead counters/expressions.
Unfortunately, I'm still getting the same result, when trying to get
coverage from Fuchsia apps (at least those using fuchsia_async, but that
may not be the specific cause):
When running
llvm-covto get the coverage report, I get the well knownand still useless message:
I can change CoverageMappingReader.cpp to avoid failing and I will see
some coverage results (maybe most of the coverage results) but there is
missing coverage as well. I don't know why the function name is not
found.
The "hack" is, change this:
to this:
I did learn that the original implementation (replacing counters and
expressions with Zero/unreachable counters), so this PR addresses that
issue. I hoped that it would fix the problem, but it didn't.
Specifically regarding the LLVM coverage adjustment (improvement?) made
in this version, compared to the reverted PR (#84797):
LLVM requires all counters with code regions be added to the coverage
map. The original dead block fix replaced the counters and expressions
with a Zero (unreachable) code region. This commit saves the original
counter or expression, without adding a statement to increment the
counter for the eliminated dead block.
r? @tmandry