[clang] [clang][CoverageMapping] do not emit gap when either end is an `ImplicitValueInitExpr` (PR #89564)

[Wentao Zhang via cfe-commits]

https://github.com/whentojump created https://github.com/llvm/llvm-project/pull/89564

Fixes #86998 

Two compiler explorer examples: [1](https://godbolt.org/#g:!((g:!((g:!((h:codeEditor,i:(filename:'1',fontScale:14,fontUsePx:'0',j:1,lang:___c,selection:(endColumn:21,endLineNumber:8,positionColumn:21,positionLineNumber:8,selectionStartColumn:21,selectionStartLineNumber:8,startColumn:21,startLineNumber:8),source:'struct+Foo+%7B%0A++++int+field1%3B%0A++++int+field2%3B%0A%7D%3B%0A%0Aint+main(void)+%7B%0A++++struct+Foo+foo+%3D+%7B%0A++++++++.field1+%3D+(%7B%0A++++++++++++switch+(0)+%7B%0A++++++++++++case+0:%0A++++++++++++++++break%3B%0A+++++++++++++//+%5E%5E%5E%5E%5E+HasTerminateStmt+set%0A++++++++++++%7D%0A++++++++++++0%3B%0A++++++++%7D),%0A++++++++//+%3C--+ImplicitValueInitExpr+introduced+for+.field2%0A++++%7D%3B%0A%7D'),l:'5',n:'0',o:'C+source+%231',t:'0')),k:61.44745998608211,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',overrides:!(),selection:(endColumn:45,endLineNumber:3,positionColumn:45,positionLineNumber:3,selectionStartColumn:45,selectionStartLineNumber:3,startColumn:45,startLineNumber:3),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:38.55254001391788,l:'3',n:'0',o:'',t:'0')),l:'2',m:100,n:'0',o:'',t:'0')),version:4), [2](https://godbolt.org/#g:!((g:!((g:!((h:codeEditor,i:(filename:'1',fontScale:14,fontUsePx:'0',j:1,lang:___c,selection:(endColumn:2,endLineNumber:12,positionColumn:2,positionLineNumber:12,selectionStartColumn:2,selectionStartLineNumber:12,startColumn:2,startLineNumber:12),source:'int+main(void)+%7B%0A++++int+arr%5B3%5D+%3D+%7B%0A++++++++%5B0%5D+%3D+(%7B%0A++++++++++++goto+L0%3B%0A+++++++++//+%5E%5E%5E%5E+HasTerminateStmt+set%0AL0:++++++++++++%0A++++++++++++0%3B%0A++++++++%7D),%0A++++++++//+%3C--+ImplicitValueInitExpr+introduced+for+subscript+%5B1%5D%0A++++++++%5B2%5D+%3D+0,%0A++++%7D%3B%0A%7D'),l:'5',n:'0',o:'C+source+%231',t:'0')),k:61.44745998608211,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',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:38.55254001391788,l:'3',n:'0',o:'',t:'0')),l:'2',m:100,n:'0',o:'',t:'0')),version:4)

Cause:

1. When visiting AST and generating mapping regions, a [region terminator](https://github.com/llvm/llvm-project/blob/llvmorg-18.1.4/clang/lib/CodeGen/CoverageMappingGen.cpp#L1197) (like `break` and `goto`) is likely followed by a stmt with `<invalid sloc>` (like `ImplicitValueInitExpr`).
2. Because a terminator is seen, the below branch will be executed when visiting the 2nd stmt:

    https://github.com/llvm/llvm-project/blob/e6c3289804a67ea0bb6a86fadbe454dd93b8d855/clang/lib/CodeGen/CoverageMappingGen.cpp#L1375-L1376

3. However, the 2nd stmt doesn't have a valid source location and will fail some assertions in `findGapAreaBetween()`.







>From 73e29e5dc47bfdab0708476eb5961c70de59a6cd Mon Sep 17 00:00:00 2001
From: Wentao Zhang <zhangwt1997 at gmail.com>
Date: Sun, 21 Apr 2024 21:27:01 -0500
Subject: [PATCH] [clang][CoverageMapping] do not emit gap when either end is
 an ImplicitValueInitExpr

---
 clang/lib/CodeGen/CoverageMappingGen.cpp | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/clang/lib/CodeGen/CoverageMappingGen.cpp b/clang/lib/CodeGen/CoverageMappingGen.cpp
index 64c39c5de351c7..45296ff9cfb5e3 100644
--- a/clang/lib/CodeGen/CoverageMappingGen.cpp
+++ b/clang/lib/CodeGen/CoverageMappingGen.cpp
@@ -1370,7 +1370,9 @@ struct CounterCoverageMappingBuilder
         // If last statement contains terminate statements, add a gap area
         // between the two statements. Skipping attributed statements, because
         // they don't have valid start location.
-        if (LastStmt && HasTerminateStmt && !isa<AttributedStmt>(Child)) {
+        if (LastStmt && HasTerminateStmt && !isa<AttributedStmt>(Child) &&
+            !isa<ImplicitValueInitExpr>(Child) &&
+            !isa<ImplicitValueInitExpr>(LastStmt)) {
           auto Gap = findGapAreaBetween(getEnd(LastStmt), getStart(Child));
           if (Gap)
             fillGapAreaWithCount(Gap->getBegin(), Gap->getEnd(),