[clang] [analyzer] Allow recurisve functions to be trivial. (PR #91876)

[Ryosuke Niwa via cfe-commits]

https://github.com/rniwa updated https://github.com/llvm/llvm-project/pull/91876

>From a4b877b240ede15260f08fcb4a4622dd45a13d0a Mon Sep 17 00:00:00 2001
From: Ryosuke Niwa <rniwa at apple.com>
Date: Sat, 11 May 2024 20:18:52 -0700
Subject: [PATCH] [analyzer] Allow recursive functions to be trivial.

---
 .../Checkers/WebKit/PtrTypesSemantics.cpp      | 18 +++++++++---------
 .../Checkers/WebKit/uncounted-obj-arg.cpp      |  6 ++++++
 2 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp b/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp
index ad493587affa0..dd930ea4b4ab5 100644
--- a/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp
@@ -498,22 +498,22 @@ class TrivialFunctionAnalysisVisitor
 
 bool TrivialFunctionAnalysis::isTrivialImpl(
     const Decl *D, TrivialFunctionAnalysis::CacheTy &Cache) {
-  // If the function isn't in the cache, conservatively assume that
-  // it's not trivial until analysis completes. This makes every recursive
-  // function non-trivial. This also guarantees that each function
-  // will be scanned at most once.
-  auto [It, IsNew] = Cache.insert(std::make_pair(D, false));
+  // Treat every recursive function as trivial until otherwise proven.
+  // This guarantees each function is evaluated at most once.
+  auto [It, IsNew] = Cache.insert(std::make_pair(D, true));
   if (!IsNew)
     return It->second;
 
   const Stmt *Body = D->getBody();
-  if (!Body)
-    return false;
+  if (!Body) {
+    Cache[D] = false;
+    return false;    
+  }
 
   TrivialFunctionAnalysisVisitor V(Cache);
   bool Result = V.Visit(Body);
-  if (Result)
-    Cache[D] = true;
+  if (!Result)
+    Cache[D] = false;
 
   return Result;
 }
diff --git a/clang/test/Analysis/Checkers/WebKit/uncounted-obj-arg.cpp b/clang/test/Analysis/Checkers/WebKit/uncounted-obj-arg.cpp
index 073f3252160ee..39bc76197d204 100644
--- a/clang/test/Analysis/Checkers/WebKit/uncounted-obj-arg.cpp
+++ b/clang/test/Analysis/Checkers/WebKit/uncounted-obj-arg.cpp
@@ -181,6 +181,8 @@ class RefCounted {
   void method();
   void someFunction();
   int otherFunction();
+  unsigned recursiveFunction(int n) { return !n ? 1 : recursiveFunction(n - 1);  }
+  unsigned recursiveComplexFunction(int n) { return !n ? otherFunction() : recursiveComplexFunction(n - 1);  }
 
   int trivial1() { return 123; }
   float trivial2() { return 0.3; }
@@ -417,6 +419,10 @@ class UnrelatedClass {
     RefCounted::singleton().trivial18(); // no-warning
     RefCounted::singleton().someFunction(); // no-warning
 
+    getFieldTrivial().recursiveFunction(7); // no-warning
+    getFieldTrivial().recursiveComplexFunction(9);
+    // expected-warning at -1{{Call argument for 'this' parameter is uncounted and unsafe}}
+
     getFieldTrivial().someFunction();
     // expected-warning at -1{{Call argument for 'this' parameter is uncounted and unsafe}}
     getFieldTrivial().nonTrivial1();