[PATCH] D67292: [clang-tidy] Fix bug in bugprone-use-after-move check

[Yitzhak Mandelbaum via Phabricator via cfe-commits]

ymandel created this revision.
ymandel added a reviewer: gribozavr.
Herald added a subscriber: xazax.hun.
Herald added a project: clang.

The bugprone-use-after-move check exhibits false positives for certain uses of
the C++17 if/switch init statements. These false positives are caused by a bug
in the ExprSequence calculations.

This revision adds tests for the false positives and fixes the corresponding
sequence calculation.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D67292

Files:
  clang-tools-extra/clang-tidy/utils/ExprSequence.cpp
  clang-tools-extra/test/clang-tidy/bugprone-use-after-move.cpp


Index: clang-tools-extra/test/clang-tidy/bugprone-use-after-move.cpp
===================================================================
--- clang-tools-extra/test/clang-tidy/bugprone-use-after-move.cpp
+++ clang-tools-extra/test/clang-tidy/bugprone-use-after-move.cpp
@@ -1190,6 +1190,12 @@
       std::move(a2);
     }
   }
+  for (int i = 0; i < 10; ++i) {
+    A a1;
+    if (A a2 = std::move(a1); a2) {
+      std::move(a2);
+    }
+  }
   for (int i = 0; i < 10; ++i) {
     A a1;
     if (A a2 = std::move(a1); A a3 = std::move(a2)) {
@@ -1199,6 +1205,13 @@
   while (A a = A()) {
     std::move(a);
   }
+  for (int i = 0; i < 10; ++i) {
+    A a1;
+    switch (A a2 = std::move(a1); a2) {
+      case true:
+        std::move(a2);
+    }
+  }
   for (int i = 0; i < 10; ++i) {
     A a1;
     switch (A a2 = a1; A a3 = std::move(a2)) {
Index: clang-tools-extra/clang-tidy/utils/ExprSequence.cpp
===================================================================
--- clang-tools-extra/clang-tidy/utils/ExprSequence.cpp
+++ clang-tools-extra/clang-tidy/utils/ExprSequence.cpp
@@ -145,17 +145,24 @@
         return ForRange->getBody();
     } else if (const auto *TheIfStmt = dyn_cast<IfStmt>(Parent)) {
       // If statement:
-      // - Sequence init statement before variable declaration.
+      // - Sequence init statement before variable declaration, if present;
+      //   before condition evaluation, otherwise.
       // - Sequence variable declaration (along with the expression used to
       //   initialize it) before the evaluation of the condition.
-      if (S == TheIfStmt->getInit())
-        return TheIfStmt->getConditionVariableDeclStmt();
+      if (S == TheIfStmt->getInit()) {
+        if (TheIfStmt->getConditionVariableDeclStmt() != nullptr)
+          return TheIfStmt->getConditionVariableDeclStmt();
+        return TheIfStmt->getCond();
+      }
       if (S == TheIfStmt->getConditionVariableDeclStmt())
         return TheIfStmt->getCond();
     } else if (const auto *TheSwitchStmt = dyn_cast<SwitchStmt>(Parent)) {
       // Ditto for switch statements.
-      if (S == TheSwitchStmt->getInit())
-        return TheSwitchStmt->getConditionVariableDeclStmt();
+      if (S == TheSwitchStmt->getInit()) {
+        if (TheSwitchStmt->getConditionVariableDeclStmt() != nullptr)
+          return TheSwitchStmt->getConditionVariableDeclStmt();
+        return TheSwitchStmt->getCond();
+      }
       if (S == TheSwitchStmt->getConditionVariableDeclStmt())
         return TheSwitchStmt->getCond();
     } else if (const auto *TheWhileStmt = dyn_cast<WhileStmt>(Parent)) {


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