[clang][nullability] Propagate storage location / value of `++`/`--` operators. (#94217)

To avoid generating unnecessary values, we don't create a new value but
instead
leave it to the specific analysis to do this if desired.

clang/lib/Analysis/FlowSensitive/Transfer.cpp

diff --git a/clang/lib/Analysis/FlowSensitive/Transfer.cpp b/clang/lib/Analysis/FlowSensitive/Transfer.cpp
index 4214488..d161b23 100644
--- a/clang/lib/Analysis/FlowSensitive/Transfer.cpp
+++ b/clang/lib/Analysis/FlowSensitive/Transfer.cpp
@@ -382,6 +382,20 @@
       Env.setValue(*S, Env.makeNot(*SubExprVal));
       break;
     }
+    case UO_PreInc:
+    case UO_PreDec:
+      // Propagate the storage location, but don't create a new value; to
+      // avoid generating unnecessary values, we leave it to the specific
+      // analysis to do this if desired.
+      propagateStorageLocation(*S->getSubExpr(), *S, Env);
+      break;
+    case UO_PostInc:
+    case UO_PostDec:
+      // Propagate the old value, but don't create a new value; to avoid
+      // generating unnecessary values, we leave it to the specific analysis
+      // to do this if desired.
+      propagateValue(*S->getSubExpr(), *S, Env);
+      break;
     default:
       break;
     }

clang/unittests/Analysis/FlowSensitive/TransferTest.cpp

diff --git a/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp b/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
index 5c0582e..cdaee9b 100644
--- a/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
+++ b/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
@@ -3760,6 +3760,42 @@
       });
 }
 
+TEST(TransferTest, Preincrement) {
+  std::string Code = R"(
+    void target(int I) {
+      int &IRef = ++I;
+      // [[p]]
+    }
+  )";
+  runDataflow(
+      Code,
+      [](const llvm::StringMap<DataflowAnalysisState<NoopLattice>> &Results,
+         ASTContext &ASTCtx) {
+        const Environment &Env = getEnvironmentAtAnnotation(Results, "p");
+
+        EXPECT_EQ(&getLocForDecl(ASTCtx, Env, "IRef"),
+                  &getLocForDecl(ASTCtx, Env, "I"));
+      });
+}
+
+TEST(TransferTest, Postincrement) {
+  std::string Code = R"(
+    void target(int I) {
+      int OldVal = I++;
+      // [[p]]
+    }
+  )";
+  runDataflow(
+      Code,
+      [](const llvm::StringMap<DataflowAnalysisState<NoopLattice>> &Results,
+         ASTContext &ASTCtx) {
+        const Environment &Env = getEnvironmentAtAnnotation(Results, "p");
+
+        EXPECT_EQ(&getValueForDecl(ASTCtx, Env, "OldVal"),
+                  &getValueForDecl(ASTCtx, Env, "I"));
+      });
+}
+
 TEST(TransferTest, CannotAnalyzeFunctionTemplate) {
   std::string Code = R"(
     template <typename T>