[clang-tools-extra] r371396 - [clang-tidy] Fix bug in bugprone-use-after-move check

[Yitzhak Mandelbaum via cfe-commits]

Author: ymandel
Date: Mon Sep  9 05:59:14 2019
New Revision: 371396

URL: http://llvm.org/viewvc/llvm-project?rev=371396&view=rev
Log:
[clang-tidy] Fix bug in bugprone-use-after-move check

Summary:
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.

Reviewers: gribozavr

Subscribers: xazax.hun, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D67292

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

Modified: clang-tools-extra/trunk/clang-tidy/utils/ExprSequence.cpp
URL: http://llvm.org/viewvc/llvm-project/clang-tools-extra/trunk/clang-tidy/utils/ExprSequence.cpp?rev=371396&r1=371395&r2=371396&view=diff
==============================================================================
--- clang-tools-extra/trunk/clang-tidy/utils/ExprSequence.cpp (original)
+++ clang-tools-extra/trunk/clang-tidy/utils/ExprSequence.cpp Mon Sep  9 05:59:14 2019
@@ -145,17 +145,24 @@ const Stmt *ExprSequence::getSequenceSuc
         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)) {

Modified: clang-tools-extra/trunk/test/clang-tidy/bugprone-use-after-move.cpp
URL: http://llvm.org/viewvc/llvm-project/clang-tools-extra/trunk/test/clang-tidy/bugprone-use-after-move.cpp?rev=371396&r1=371395&r2=371396&view=diff
==============================================================================
--- clang-tools-extra/trunk/test/clang-tidy/bugprone-use-after-move.cpp (original)
+++ clang-tools-extra/trunk/test/clang-tidy/bugprone-use-after-move.cpp Mon Sep  9 05:59:14 2019
@@ -1182,7 +1182,10 @@ void forRangeSequences() {
 
 // If a variable is declared in an if, while or switch statement, the init
 // statement (for if and switch) is sequenced before the variable declaration,
-// which in turn is sequenced before the evaluation of the condition.
+// which in turn is sequenced before the evaluation of the condition. We place
+// all tests inside a for loop to ensure that the checker understands the
+// sequencing. If it didn't, then the loop would trigger the "moved twice"
+// logic.
 void ifWhileAndSwitchSequenceInitDeclAndCondition() {
   for (int i = 0; i < 10; ++i) {
     A a1;
@@ -1192,15 +1195,44 @@ void ifWhileAndSwitchSequenceInitDeclAnd
   }
   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)) {
       std::move(a3);
     }
   }
+  for (int i = 0; i < 10; ++i) {
+    // init followed by condition with move, but without variable declaration.
+    if (A a1; A(std::move(a1)).getInt() > 0) {}
+  }
+  for (int i = 0; i < 10; ++i) {
+    if (A a1; A(std::move(a1)).getInt() > a1.getInt()) {}
+    // CHECK-NOTES: [[@LINE-1]]:43: warning: 'a1' used after it was moved
+    // CHECK-NOTES: [[@LINE-2]]:15: note: move occurred here
+    // CHECK-NOTES: [[@LINE-3]]:43: note: the use and move are unsequenced
+  }
+  for (int i = 0; i < 10; ++i) {
+    A a1;
+    if (A a2 = std::move(a1); A(a1) > 0) {}
+    // CHECK-NOTES: [[@LINE-1]]:33: warning: 'a1' used after it was moved
+    // CHECK-NOTES: [[@LINE-2]]:16: note: move occurred here
+  }
   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)) {
       case true:
         std::move(a3);