[llvm-branch-commits] [clang] release/18.x: [clang][CodeGen] Keep processing the rest of AST after encountering unsupported MC/DC expressions (#82464) (PR #82866)

[via llvm-branch-commits]

https://github.com/llvmbot updated https://github.com/llvm/llvm-project/pull/82866

>From b058dd52590462f564238275527e7f061ff9e08a Mon Sep 17 00:00:00 2001
From: Wentao Zhang <35722712+whentojump at users.noreply.github.com>
Date: Thu, 22 Feb 2024 16:04:25 -0600
Subject: [PATCH] [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.

(cherry picked from commit d4bfca3b2e673789f7c278d46a199ae8910ddd37)
---
 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 5d7c3847745762..fb4e86e8bd8053 100644
--- a/clang/lib/CodeGen/CodeGenPGO.cpp
+++ b/clang/lib/CodeGen/CodeGenPGO.cpp
@@ -240,9 +240,12 @@ 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());
@@ -293,7 +296,7 @@ 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?
@@ -304,7 +307,7 @@ 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