[Sema] Add -Wpointer-compare

This patch adds a warning that diagnoses comparisons of pointers to
'\0'. This is often indicative of a bug (e.g. the user might've
forgotten to dereference the pointer).

Patch by Elaina Guan!

Differential Revision: https://reviews.llvm.org/D65595

llvm-svn: 367940
This commit is contained in:
George Burgess IV 2019-08-05 22:15:40 +00:00
parent dcdbe6515b
commit f708f0a243
4 changed files with 84 additions and 0 deletions
clang

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@ -3296,6 +3296,10 @@ def warn_impcast_bool_to_null_pointer : Warning<
def warn_non_literal_null_pointer : Warning<
"expression which evaluates to zero treated as a null pointer constant of "
"type %0">, InGroup<NonLiteralNullConversion>;
def warn_pointer_compare : Warning<
"comparing a pointer to a null character constant; did you mean "
"to compare to %select{NULL|(void *)0}0?">,
InGroup<DiagGroup<"pointer-compare">>;
def warn_impcast_null_pointer_to_integer : Warning<
"implicit conversion of %select{NULL|nullptr}0 constant to %1">,
InGroup<NullConversion>;

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@ -10022,6 +10022,7 @@ public:
QualType CheckShiftOperands( // C99 6.5.7
ExprResult &LHS, ExprResult &RHS, SourceLocation Loc,
BinaryOperatorKind Opc, bool IsCompAssign = false);
void CheckPtrComparisonWithNullChar(ExprResult &E, ExprResult &NullE);
QualType CheckCompareOperands( // C99 6.5.8/9
ExprResult &LHS, ExprResult &RHS, SourceLocation Loc,
BinaryOperatorKind Opc);

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@ -10443,6 +10443,32 @@ static QualType checkArithmeticOrEnumeralCompare(Sema &S, ExprResult &LHS,
return S.Context.getLogicalOperationType();
}
void Sema::CheckPtrComparisonWithNullChar(ExprResult &E, ExprResult &NullE) {
if (!NullE.get()->getType()->isAnyPointerType())
return;
int NullValue = PP.isMacroDefined("NULL") ? 0 : 1;
if (!E.get()->getType()->isAnyPointerType() &&
E.get()->isNullPointerConstant(Context,
Expr::NPC_ValueDependentIsNotNull) ==
Expr::NPCK_ZeroExpression) {
if (const auto *CL = dyn_cast<CharacterLiteral>(E.get())) {
if (CL->getValue() == 0)
Diag(E.get()->getExprLoc(), diag::warn_pointer_compare)
<< NullValue
<< FixItHint::CreateReplacement(E.get()->getExprLoc(),
NullValue ? "NULL" : "(void *)0");
} else if (const auto *CE = dyn_cast<CStyleCastExpr>(E.get())) {
TypeSourceInfo *TI = CE->getTypeInfoAsWritten();
QualType T = Context.getCanonicalType(TI->getType()).getUnqualifiedType();
if (T == Context.CharTy)
Diag(E.get()->getExprLoc(), diag::warn_pointer_compare)
<< NullValue
<< FixItHint::CreateReplacement(E.get()->getExprLoc(),
NullValue ? "NULL" : "(void *)0");
}
}
}
// C99 6.5.8, C++ [expr.rel]
QualType Sema::CheckCompareOperands(ExprResult &LHS, ExprResult &RHS,
SourceLocation Loc,
@ -10476,6 +10502,10 @@ QualType Sema::CheckCompareOperands(ExprResult &LHS, ExprResult &RHS,
}
checkArithmeticNull(*this, LHS, RHS, Loc, /*IsCompare=*/true);
if (!getLangOpts().CPlusPlus && BinaryOperator::isEqualityOp(Opc)) {
CheckPtrComparisonWithNullChar(LHS, RHS);
CheckPtrComparisonWithNullChar(RHS, LHS);
}
// Handle vector comparisons separately.
if (LHS.get()->getType()->isVectorType() ||

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@ -0,0 +1,49 @@
// RUN: %clang_cc1 -fsyntax-only -verify -Wall %s
int test1(int *a) {
return a == '\0'; // expected-warning {{comparing a pointer to a null character constant; did you mean to compare to (void *)0?}}
}
int test2(int *a) {
return '\0' == a; // expected-warning {{comparing a pointer to a null character constant; did you mean to compare to (void *)0?}}
}
int test3(int *a) {
return a == L'\0'; // expected-warning {{comparing a pointer to a null character constant; did you mean to compare to (void *)0?}}
}
int test4(int *a) {
return a == u'\0'; // expected-warning {{comparing a pointer to a null character constant; did you mean to compare to (void *)0?}}
}
int test5(int *a) {
return a == U'\0'; // expected-warning {{comparing a pointer to a null character constant; did you mean to compare to (void *)0?}}
}
int test6(int *a) {
return a == (char)0; // expected-warning {{comparing a pointer to a null character constant; did you mean to compare to (void *)0?}}
}
typedef char my_char;
int test7(int *a) {
return a == (my_char)0;
// expected-warning@-1 {{comparing a pointer to a null character constant; did you mean to compare to (void *)0?}}
}
int test8(int *a) {
return a != '\0'; // expected-warning {{comparing a pointer to a null character constant; did you mean to compare to (void *)0?}}
}
#define NULL (void *)0
int test9(int *a) {
return a == '\0'; // expected-warning {{comparing a pointer to a null character constant; did you mean to compare to NULL?}}
}
#define MYCHAR char
int test10(int *a) {
return a == (MYCHAR)0; // expected-warning {{comparing a pointer to a null character constant; did you mean to compare to NULL?}}
}
int test11(int *a) {
return a > '\0';
}