[PATCH] D122271: [Clang] -Wunused-but-set-variable warning - handle also pre/post unary operators

[Dávid Bolvanský via Phabricator via cfe-commits]

xbolva00 created this revision.
xbolva00 added reviewers: efriedma, yonghong-song.
Herald added a project: All.
xbolva00 requested review of this revision.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.

Clang fails to diagnose:

  void test() {
      int j = 0;
      for (int i = 0; i < 1000; i++)
              j++;
      return;
  }

Reason: Missing support for UnaryOperator.

We should not warn with volatile variables... so add check for it.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D122271

Files:
  clang/lib/Sema/SemaExprCXX.cpp
  clang/test/Sema/warn-unused-but-set-variables.c
  clang/test/SemaCXX/warn-unused-but-set-variables-cpp.cpp


Index: clang/test/SemaCXX/warn-unused-but-set-variables-cpp.cpp
===================================================================
--- clang/test/SemaCXX/warn-unused-but-set-variables-cpp.cpp
+++ clang/test/SemaCXX/warn-unused-but-set-variables-cpp.cpp
@@ -7,6 +7,7 @@
 struct __attribute__((warn_unused)) SWarnUnused {
   int j;
   void operator +=(int);
+  void operator ++();
 };
 
 int f0() {
@@ -62,3 +63,9 @@
   SWarnUnused swu;
   swu += n;
 }
+
+template <typename T> void f5() {
+  // Don't warn for overloaded pre/post operators in template code.
+  SWarnUnused swu;
+  ++swu;
+}
Index: clang/test/Sema/warn-unused-but-set-variables.c
===================================================================
--- clang/test/Sema/warn-unused-but-set-variables.c
+++ clang/test/Sema/warn-unused-but-set-variables.c
@@ -73,3 +73,20 @@
   __attribute__((__cleanup__(for_cleanup))) int x;
   x = 5;
 }
+
+void f4(void) {
+  int x1 = 0; // expected-warning{{variable 'x1' set but not used}}
+  x1++;
+  int x2 = 0; // expected-warning{{variable 'x2' set but not used}}
+  x2--;
+  int x3 = 0; // expected-warning{{variable 'x3' set but not used}}
+  ++x3;
+  int x4 = 0; // expected-warning{{variable 'x4' set but not used}}
+  --x4;
+
+  volatile int v1 = 0;
+  ++v1;
+  typedef volatile int volint;
+  volint v2 = 0;
+  v2++;
+}
Index: clang/lib/Sema/SemaExprCXX.cpp
===================================================================
--- clang/lib/Sema/SemaExprCXX.cpp
+++ clang/lib/Sema/SemaExprCXX.cpp
@@ -7926,6 +7926,7 @@
     Expr *E, llvm::DenseMap<const VarDecl *, int> &RefsMinusAssignments) {
   DeclRefExpr *LHS = nullptr;
   bool IsCompoundAssign = false;
+  bool isIncrementDecrementUnaryOp = false;
   if (BinaryOperator *BO = dyn_cast<BinaryOperator>(E)) {
     if (BO->getLHS()->getType()->isDependentType() ||
         BO->getRHS()->getType()->isDependentType()) {
@@ -7940,6 +7941,11 @@
     if (COCE->getOperator() != OO_Equal)
       return;
     LHS = dyn_cast<DeclRefExpr>(COCE->getArg(0));
+  } else if (UnaryOperator *UO = dyn_cast<UnaryOperator>(E)) {
+    if (!UO->isIncrementDecrementOp())
+      return;
+    isIncrementDecrementUnaryOp = true;
+    LHS = dyn_cast<DeclRefExpr>(UO->getSubExpr());
   }
   if (!LHS)
     return;
@@ -7947,8 +7953,10 @@
   if (!VD)
     return;
   // Don't decrement RefsMinusAssignments if volatile variable with compound
-  // assignment (+=, ...) to avoid potential unused-but-set-variable warning.
-  if (IsCompoundAssign && VD->getType().isVolatileQualified())
+  // assignment (+=, ...) or increment/decrement unary operator to avoid
+  // potential unused-but-set-variable warning.
+  if ((IsCompoundAssign || isIncrementDecrementUnaryOp) &&
+      VD->getType().isVolatileQualified())
     return;
   auto iter = RefsMinusAssignments.find(VD);
   if (iter == RefsMinusAssignments.end())


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