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

[via cfe-commits]

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


>From dc88f5ddb98ebfb738fe26ae268d9d1f42a1957a Mon Sep 17 00:00:00 2001
From: Martin Braenne <mboehme at google.com>
Date: Mon, 3 Jun 2024 13:23:05 +0000
Subject: [PATCH] [clang][nullability] Propagate storage location / value of
 `++`/`--` operators.

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 | 14 ++++++++
 .../Analysis/FlowSensitive/TransferTest.cpp   | 36 +++++++++++++++++++
 2 files changed, 50 insertions(+)

diff --git a/clang/lib/Analysis/FlowSensitive/Transfer.cpp b/clang/lib/Analysis/FlowSensitive/Transfer.cpp
index 4214488c98e5d..d161b231c0b6f 100644
--- a/clang/lib/Analysis/FlowSensitive/Transfer.cpp
+++ b/clang/lib/Analysis/FlowSensitive/Transfer.cpp
@@ -382,6 +382,20 @@ class TransferVisitor : public ConstStmtVisitor<TransferVisitor> {
       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;
     }
diff --git a/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp b/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
index 5c0582e872eb0..cdaee9b2c9288 100644
--- a/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
+++ b/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
@@ -3760,6 +3760,42 @@ TEST(TransferTest, AddrOfReference) {
       });
 }
 
+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>