[clang-tidy] Fix performance-unnecessary-value-param (#109145)

This patch essentially reverts #108674 while adding a testcase that
triggers a crash in clang-tidy.

Fixes #108963.

Author: kazutakahirata

clang-tools-extra/test/clang-tidy/checkers/performance/unnecessary-value-param-crash.cpp

@@ -0,0 +1,23 @@
+// RUN: %check_clang_tidy  -std=c++14-or-later %s performance-unnecessary-value-param %t
+
+// The test case used to crash clang-tidy.
+// https://github.com/llvm/llvm-project/issues/108963
+
+struct A
+{
+  template<typename T> A(T&&) {}
+};
+
+struct B
+{
+  ~B();
+};
+
+struct C
+{
+  A a;
+  C(B, int i) : a(i) {}
+  // CHECK-MESSAGES: [[@LINE-1]]:6: warning: the parameter #1 is copied for each invocation but only used as a const reference; consider making it a const reference
+};
+
+C c(B(), 0);

clang/include/clang/Analysis/Analyses/ExprMutationAnalyzer.h

@@ -118,10 +118,19 @@ class FunctionParmMutationAnalyzer {
   static FunctionParmMutationAnalyzer *
   getFunctionParmMutationAnalyzer(const FunctionDecl &Func, ASTContext &Context,
                                   ExprMutationAnalyzer::Memoized &Memorized) {
-    auto [it, Inserted] = Memorized.FuncParmAnalyzer.try_emplace(&Func);
-    if (Inserted)
-      it->second = std::unique_ptr<FunctionParmMutationAnalyzer>(
-          new FunctionParmMutationAnalyzer(Func, Context, Memorized));
+    auto it = Memorized.FuncParmAnalyzer.find(&Func);
+    if (it == Memorized.FuncParmAnalyzer.end()) {
+      // Creating a new instance of FunctionParmMutationAnalyzer below may add
+      // additional elements to FuncParmAnalyzer. If we did try_emplace before
+      // creating a new instance, the returned iterator of try_emplace could be
+      // invalidated.
+      it =
+          Memorized.FuncParmAnalyzer
+              .try_emplace(&Func, std::unique_ptr<FunctionParmMutationAnalyzer>(
+                                      new FunctionParmMutationAnalyzer(
+                                          Func, Context, Memorized)))
+              .first;
+    }
     return it->getSecond().get();
   }