[clang] [clang][dataflow] Treat `BuiltinBitCastExpr` correctly in `PropagateResultObject()`. (PR #88875)

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https://github.com/martinboehme created https://github.com/llvm/llvm-project/pull/88875

This patch includes a test that assert-fails without the fix.


>From c8797bbbdb32d9f153b36b6902f8562af75fb896 Mon Sep 17 00:00:00 2001
From: Martin Braenne <mboehme at google.com>
Date: Tue, 16 Apr 2024 11:13:00 +0000
Subject: [PATCH] [clang][dataflow] Treat `BuiltinBitCastExpr` correctly in
 `PropagateResultObject()`.

This patch includes a test that assert-fails without the fix.
---
 .../FlowSensitive/DataflowEnvironment.cpp     |  6 ++++-
 .../Analysis/FlowSensitive/TransferTest.cpp   | 26 +++++++++++++++++++
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/clang/lib/Analysis/FlowSensitive/DataflowEnvironment.cpp b/clang/lib/Analysis/FlowSensitive/DataflowEnvironment.cpp
index ee2581143e1141..90eea420258764 100644
--- a/clang/lib/Analysis/FlowSensitive/DataflowEnvironment.cpp
+++ b/clang/lib/Analysis/FlowSensitive/DataflowEnvironment.cpp
@@ -505,7 +505,11 @@ class ResultObjectVisitor : public RecursiveASTVisitor<ResultObjectVisitor> {
     // below them can initialize the same object (or part of it).
     if (isa<CXXConstructExpr>(E) || isa<CallExpr>(E) || isa<LambdaExpr>(E) ||
         isa<CXXDefaultArgExpr>(E) || isa<CXXDefaultInitExpr>(E) ||
-        isa<CXXStdInitializerListExpr>(E)) {
+        isa<CXXStdInitializerListExpr>(E) ||
+        // We treat `BuiltinBitCastExpr` as an "original initializer" too as
+        // it may not even be casting from a record type -- and even if it is,
+        // the two objects are in general of unrelated type.
+        isa<BuiltinBitCastExpr>(E)) {
       return;
     }
     if (auto *Op = dyn_cast<BinaryOperator>(E);
diff --git a/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp b/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
index d8bcc3da4b8b1c..54744a2762e773 100644
--- a/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
+++ b/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
@@ -3182,6 +3182,32 @@ TEST(TransferTest, ResultObjectLocationForStdInitializerListExpr) {
       });
 }
 
+TEST(TransferTest, ResultObjectLocationForBuiltinBitCastExpr) {
+  std::string Code = R"(
+    struct S { int i; };
+    void target(int i) {
+      S s = __builtin_bit_cast(S, i);
+      // [[p]]
+    }
+  )";
+  using ast_matchers::explicitCastExpr;
+  using ast_matchers::match;
+  using ast_matchers::selectFirst;
+  using ast_matchers::traverse;
+  runDataflow(
+      Code,
+      [](const llvm::StringMap<DataflowAnalysisState<NoopLattice>> &Results,
+         ASTContext &ASTCtx) {
+        const Environment &Env = getEnvironmentAtAnnotation(Results, "p");
+
+        auto *BuiltinBitCast = selectFirst<BuiltinBitCastExpr>(
+            "cast", match(explicitCastExpr().bind("cast"), ASTCtx));
+
+        EXPECT_EQ(&Env.getResultObjectLocation(*BuiltinBitCast),
+                  &getLocForDecl<RecordStorageLocation>(ASTCtx, Env, "s"));
+      });
+}
+
 TEST(TransferTest, ResultObjectLocationPropagatesThroughConditionalOperator) {
   std::string Code = R"(
     struct A {