Currently both True/False counts were folded. It lost the information,
"It is True or False before folding." It prevented recalling branch
counts in merging template instantiations.
In `llvm-cov`, a folded branch is shown as:
- `[True: n, Folded]`
- `[Folded, False n]`
In the case If `n` is zero, a branch is reported as "uncovered". This is
distinguished from "folded" branch. When folded branches are merged,
`Folded` may be dissolved.
In the coverage map, either `Counter` is `Zero`. Currently both were
`Zero`.
Since "partial fold" has been introduced, either case in `switch` is
omitted as `Folded`.
Each `case:` in `switch` is reported as `[True: n, Folded]`, since
`False` count doesn't show meaningful value.
When `switch` doesn't have `default:`, `switch (Cond)` is reported as
`[Folded, False: n]`, since `True` count was just the sum of `case`(s).
`switch` with `default` can be considered as "the statement that doesn't
have any `False`(s)".
By storing possible test vectors instead of combinations of conditions,
the restriction is dramatically relaxed.
This introduces two options to `cc1`:
* `-fmcdc-max-conditions=32767`
* `-fmcdc-max-test-vectors=2147483646`
This change makes coverage mapping, profraw, and profdata incompatible
with Clang-18.
- Bitmap semantics changed. It is incompatible with previous format.
- `BitmapIdx` in `Decision` points to the end of the bitmap.
- Bitmap is packed per function.
- `llvm-cov` can understand `profdata` generated by `llvm-profdata-18`.
RFC:
https://discourse.llvm.org/t/rfc-coverage-new-algorithm-and-file-format-for-mc-dc/76798
--
Change(s) since llvmorg-19-init-14288-g7ead2d8c7e91
- Update compiler-rt/test/profile/ContinuousSyncMode/image-with-mcdc.c
This broke the lit tests on Mac:
https://green.lab.llvm.org/job/llvm.org/job/clang-stage1-RA/1096/
> By storing possible test vectors instead of combinations of conditions,
> the restriction is dramatically relaxed.
>
> This introduces two options to `cc1`:
>
> * `-fmcdc-max-conditions=32767`
> * `-fmcdc-max-test-vectors=2147483646`
>
> This change makes coverage mapping, profraw, and profdata incompatible
> with Clang-18.
>
> - Bitmap semantics changed. It is incompatible with previous format.
> - `BitmapIdx` in `Decision` points to the end of the bitmap.
> - Bitmap is packed per function.
> - `llvm-cov` can understand `profdata` generated by `llvm-profdata-18`.
>
> RFC:
> https://discourse.llvm.org/t/rfc-coverage-new-algorithm-and-file-format-for-mc-dc/76798
This reverts commit 7ead2d8c7e9114b3f23666209a1654939987cb30.
By storing possible test vectors instead of combinations of conditions,
the restriction is dramatically relaxed.
This introduces two options to `cc1`:
* `-fmcdc-max-conditions=32767`
* `-fmcdc-max-test-vectors=2147483646`
This change makes coverage mapping, profraw, and profdata incompatible
with Clang-18.
- Bitmap semantics changed. It is incompatible with previous format.
- `BitmapIdx` in `Decision` points to the end of the bitmap.
- Bitmap is packed per function.
- `llvm-cov` can understand `profdata` generated by `llvm-profdata-18`.
RFC:
https://discourse.llvm.org/t/rfc-coverage-new-algorithm-and-file-format-for-mc-dc/76798
The problematic program is as follows:
```shell
#define pre_a 0
#define PRE(x) pre_##x
void f(void) {
PRE(a) && 0;
}
int main(void) { return 0; }
```
in which after token concatenation (`##`), there's another nested macro
`pre_a`.
Currently only the outer expansion region will be produced. ([compiler
explorer
link](https://godbolt.org/#g:!((g:!((g:!((h:codeEditor,i:(filename:'1',fontScale:14,fontUsePx:'0',j:1,lang:___c,selection:(endColumn:29,endLineNumber:8,positionColumn:29,positionLineNumber:8,selectionStartColumn:29,selectionStartLineNumber:8,startColumn:29,startLineNumber:8),source:'%23define+pre_a+0%0A%23define+PRE(x)+pre_%23%23x%0A%0Avoid+f(void)+%7B%0A++++PRE(a)+%26%26+0%3B%0A%7D%0A%0Aint+main(void)+%7B+return+0%3B+%7D'),l:'5',n:'0',o:'C+source+%231',t:'0')),k:51.69491525423727,l:'4',n:'0',o:'',s:0,t:'0'),(g:!((g:!((h:compiler,i:(compiler:cclang_assertions_trunk,filters:(b:'0',binary:'1',binaryObject:'1',commentOnly:'0',debugCalls:'1',demangle:'0',directives:'0',execute:'0',intel:'0',libraryCode:'1',trim:'1',verboseDemangling:'0'),flagsViewOpen:'1',fontScale:14,fontUsePx:'0',j:2,lang:___c,libs:!(),options:'-fprofile-instr-generate+-fcoverage-mapping+-fcoverage-mcdc+-Xclang+-dump-coverage-mapping+',overrides:!(),selection:(endColumn:1,endLineNumber:1,positionColumn:1,positionLineNumber:1,selectionStartColumn:1,selectionStartLineNumber:1,startColumn:1,startLineNumber:1),source:1),l:'5',n:'0',o:'+x86-64+clang+(assertions+trunk)+(Editor+%231)',t:'0')),k:34.5741843594503,l:'4',m:28.903654485049834,n:'0',o:'',s:0,t:'0'),(g:!((h:output,i:(compilerName:'x86-64+clang+(trunk)',editorid:1,fontScale:14,fontUsePx:'0',j:2,wrap:'1'),l:'5',n:'0',o:'Output+of+x86-64+clang+(assertions+trunk)+(Compiler+%232)',t:'0')),header:(),l:'4',m:71.09634551495017,n:'0',o:'',s:0,t:'0')),k:48.30508474576271,l:'3',n:'0',o:'',t:'0')),l:'2',m:100,n:'0',o:'',t:'0')),version:4))
```text
f:
File 0, 4:14 -> 6:2 = #0
Decision,File 0, 5:5 -> 5:16 = M:0, C:2
Expansion,File 0, 5:5 -> 5:8 = #0 (Expanded file = 1)
File 0, 5:15 -> 5:16 = #1
Branch,File 0, 5:15 -> 5:16 = 0, 0 [2,0,0]
File 1, 2:16 -> 2:23 = #0
File 2, 1:15 -> 1:16 = #0
File 2, 1:15 -> 1:16 = #0
Branch,File 2, 1:15 -> 1:16 = 0, 0 [1,2,0]
```
The inner expansion region isn't produced because:
1. In the range-based for loop quoted below, each sloc is processed and
possibly emit a corresponding expansion region.
2. For our sloc in question, its direct parent returned by
`getIncludeOrExpansionLoc()` is a `<scratch space>`, because that's how
`##` is processed.
88b6186af3/clang/lib/CodeGen/CoverageMappingGen.cpp (L518-L520)
3. This `<scratch space>` cannot be found in the FileID mapping so
`ParentFileID` will be assigned an `std::nullopt`
88b6186af3/clang/lib/CodeGen/CoverageMappingGen.cpp (L521-L526)
4. As a result this iteration of for loop finishes early and no
expansion region is added for the sloc.
This problem gets worse with MC/DC: as the example shows, there's a
branch from File 2 but File 2 itself is missing. This will trigger
assertion failures.
The fix is more or less a workaround and takes a similar approach as
#89573.
~~Depends on #89573.~~ This includes #89573. Kudos to @chapuni!
This and #89573 together fix#87000: I tested locally, both the reduced
program and my original use case (fwiw, Linux kernel) can run
successfully.
---------
Co-authored-by: NAKAMURA Takumi <geek4civic@gmail.com>
`emitSourceRegions()` has bugs to emit malformed MC/DC coverage
mappings. They were detected in `llvm-cov` as the crash.
Detect inconsistencies earlier in `clang` with assertions.
* mcdc-scratch-space.c covers #87000.
