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

[Wentao Zhang via cfe-commits]

https://github.com/whentojump created https://github.com/llvm/llvm-project/pull/82464

Currently, upon seeing [unsupported decisions](https://clang.llvm.org/docs/SourceBasedCodeCoverage.html#mc-dc-instrumentation) (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:

```c
{ // 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.

>From 67a2c10b044e0e9c2eceb6646300e546ee990e0b Mon Sep 17 00:00:00 2001
From: Wentao Zhang <zhangwt1997 at gmail.com>
Date: Wed, 21 Feb 2024 01:48:11 -0500
Subject: [PATCH] [clang][CodeGen] Keep processing the rest of AST after
 encountering unsupported MC/DC expressions

---
 clang/lib/CodeGen/CodeGenPGO.cpp | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/clang/lib/CodeGen/CodeGenPGO.cpp b/clang/lib/CodeGen/CodeGenPGO.cpp
index 48c5e68a3b7ba4..1ef7be3c72593d 100644
--- a/clang/lib/CodeGen/CodeGenPGO.cpp
+++ b/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