[clang][CodeGen] Keep processing the rest of AST after encountering unsupported MC/DC expressions (#82464)

Currently, upon seeing unsupported decisions (more than 6 conditions, or split nesting), the post-visitor hook dataTraverseStmtPost() returns a false. As a result, in the rest of tree even supported decisions will be skipped as well. Like in the below code: { // CompoundStmt a && b; // 1: BinaryOperator (supported) a && foo(b && c); // 2: BinaryOperator (not yet supported due to split // nesting) a && b; // 3: BinaryOperator (supported) } Decision 3 will not be processed at all. And only one "Decision" region will be emitted. Compiler explorer example: https://godbolt.org/z/Px61sesoo We hope to process such cases and emit two "Decision" regions (1 and 3) in the above example.

Author: whentojump

clang/lib/CodeGen/CodeGenPGO.cpp

@@ -239,9 +239,12 @@ struct MapRegionCounters : public RecursiveASTVisitor<MapRegionCounters> {
  if (MCDCMaxCond == 0)
  return true;
 
- /// At the top of the logical operator nest, reset the number of conditions.
- if (LogOpStack.empty())
+ /// At the top of the logical operator nest, reset the number of conditions,
+ /// also forget previously seen split nesting cases.
+ if (LogOpStack.empty()) {
  NumCond = 0;
+ SplitNestedLogicalOp = false;
+ }
 
  if (const Expr *E = dyn_cast<Expr>(S)) {
  const BinaryOperator *BinOp = dyn_cast<BinaryOperator>(E->IgnoreParens());
@@ -292,7 +295,7 @@ struct MapRegionCounters : public RecursiveASTVisitor<MapRegionCounters> {
  "contains an operation with a nested boolean expression. "
  "Expression will not be covered");
  Diag.Report(S->getBeginLoc(), DiagID);
- return false;
+ return true;
  }
 
  /// Was the maximum number of conditions encountered?
@@ -303,7 +306,7 @@ struct MapRegionCounters : public RecursiveASTVisitor<MapRegionCounters> {
  "number of conditions (%0) exceeds max (%1). "
  "Expression will not be covered");
  Diag.Report(S->getBeginLoc(), DiagID) << NumCond << MCDCMaxCond;
- return false;
+ return true;
  }
 
  // Otherwise, allocate the number of bytes required for the bitmap