| #
f9e9e599 |
| 24-May-2024 |
Wentao Zhang <35722712+whentojump@users.noreply.github.com> |
[Coverage][Expansion] handle nested macros in scratch space (#89869)
The problematic program is as follows:
```shell
#define pre_a 0
#define PRE(x) pre_##x
void f(void) {
PRE(a) && 0;
[Coverage][Expansion] handle nested macros in scratch space (#89869)
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.
https://github.com/llvm/llvm-project/blob/88b6186af3908c55b357858eb348b5143f21c289/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`
https://github.com/llvm/llvm-project/blob/88b6186af3908c55b357858eb348b5143f21c289/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>
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