[Diagnostics] Implement -Wsizeof-pointer-div

Summary:
void test(int *arr) {
    int arr_len = sizeof(arr) / sizeof(*arr);  // warn, incorrect way to compute number of array elements
}

Enabled under -Wall (same behaviour as GCC)

Reviewers: rsmith, MTC, aaron.ballman

Reviewed By: aaron.ballman

Subscribers: MTC, thakis, jfb, cfe-commits

Differential Revision: https://reviews.llvm.org/D52949

llvm-svn: 345847

1 files changed, 30 insertions, 2 deletions

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index ecda5be..d7fc1aa 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -8726,6 +8726,32 @@ static void checkArithmeticNull(Sema &S, ExprResult &LHS, ExprResult &RHS,
       << LHS.get()->getSourceRange() << RHS.get()->getSourceRange();
 }
 
+static void DiagnoseDivisionSizeofPointer(Sema &S, Expr *LHS, Expr *RHS,
+                                          SourceLocation Loc) {
+  const auto *LUE = dyn_cast<UnaryExprOrTypeTraitExpr>(LHS);
+  const auto *RUE = dyn_cast<UnaryExprOrTypeTraitExpr>(RHS);
+  if (!LUE || !RUE)
+    return;
+  if (LUE->getKind() != UETT_SizeOf || LUE->isArgumentType() ||
+      RUE->getKind() != UETT_SizeOf)
+    return;
+
+  QualType LHSTy = LUE->getArgumentExpr()->IgnoreParens()->getType();
+  QualType RHSTy;
+
+  if (RUE->isArgumentType())
+    RHSTy = RUE->getArgumentType();
+  else
+    RHSTy = RUE->getArgumentExpr()->IgnoreParens()->getType();
+
+  if (!LHSTy->isPointerType() || RHSTy->isPointerType())
+    return;
+  if (LHSTy->getPointeeType() != RHSTy)
+    return;
+
+  S.Diag(Loc, diag::warn_division_sizeof_ptr) << LHS << LHS->getSourceRange();
+}
+
 static void DiagnoseBadDivideOrRemainderValues(Sema& S, ExprResult &LHS,
                                                ExprResult &RHS,
                                                SourceLocation Loc, bool IsDiv) {
@@ -8756,8 +8782,10 @@ QualType Sema::CheckMultiplyDivideOperands(ExprResult &LHS, ExprResult &RHS,
 
   if (compType.isNull() || !compType->isArithmeticType())
     return InvalidOperands(Loc, LHS, RHS);
-  if (IsDiv)
+  if (IsDiv) {
     DiagnoseBadDivideOrRemainderValues(*this, LHS, RHS, Loc, IsDiv);
+    DiagnoseDivisionSizeofPointer(*this, LHS.get(), RHS.get(), Loc);
+  }
   return compType;
 }
 
@@ -16603,4 +16631,4 @@ ExprResult Sema::ActOnObjCAvailabilityCheckExpr(
 
   return new (Context)
       ObjCAvailabilityCheckExpr(Version, AtLoc, RParen, Context.BoolTy);
-}
+}
\ No newline at end of file