[Sema] Re-land: Diagnose tautological comparison with type's min/max values
The first attempt, rL315614 was reverted because one libcxx
test broke, and i did not know at the time how to deal with it.
Summary:
Currently, clang only diagnoses completely out-of-range comparisons (e.g. `char` and constant `300`),
and comparisons of unsigned and `0`. But gcc also does diagnose the comparisons with the
`std::numeric_limits<>::max()` / `std::numeric_limits<>::min()` so to speak
Finally Fixes https://bugs.llvm.org/show_bug.cgi?id=34147
Continuation of https://reviews.llvm.org/D37565
Reviewers: rjmccall, rsmith, aaron.ballman
Reviewed By: rsmith
Subscribers: rtrieu, jroelofs, cfe-commits
Tags: #clang
Differential Revision: https://reviews.llvm.org/D38101
llvm-svn: 315875
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index cd534b2..a440606 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -8556,19 +8556,71 @@
void AnalyzeImplicitConversions(Sema &S, Expr *E, SourceLocation CC);
-bool IsZero(Sema &S, Expr *E) {
+bool IsEnumConstOrFromMacro(Sema &S, Expr *E) {
// Suppress cases where we are comparing against an enum constant.
if (const DeclRefExpr *DR =
dyn_cast<DeclRefExpr>(E->IgnoreParenImpCasts()))
if (isa<EnumConstantDecl>(DR->getDecl()))
- return false;
+ return true;
// Suppress cases where the '0' value is expanded from a macro.
if (E->getLocStart().isMacroID())
- return false;
+ return true;
- llvm::APSInt Value;
- return E->isIntegerConstantExpr(Value, S.Context) && Value == 0;
+ return false;
+}
+
+bool isNonBooleanIntegerValue(Expr *E) {
+ return !E->isKnownToHaveBooleanValue() && E->getType()->isIntegerType();
+}
+
+bool isNonBooleanUnsignedValue(Expr *E) {
+ // We are checking that the expression is not known to have boolean value,
+ // is an integer type; and is either unsigned after implicit casts,
+ // or was unsigned before implicit casts.
+ return isNonBooleanIntegerValue(E) &&
+ (!E->getType()->isSignedIntegerType() ||
+ !E->IgnoreParenImpCasts()->getType()->isSignedIntegerType());
+}
+
+enum class LimitType {
+ Max, // e.g. 32767 for short
+ Min // e.g. -32768 for short
+};
+
+/// Checks whether Expr 'Constant' may be the
+/// std::numeric_limits<>::max() or std::numeric_limits<>::min()
+/// of the Expr 'Other'. If true, then returns the limit type (min or max).
+/// The Value is the evaluation of Constant
+llvm::Optional<LimitType> IsTypeLimit(Sema &S, Expr *Constant, Expr *Other,
+ const llvm::APSInt &Value) {
+ if (IsEnumConstOrFromMacro(S, Constant))
+ return llvm::Optional<LimitType>();
+
+ if (isNonBooleanUnsignedValue(Other) && Value == 0)
+ return LimitType::Min;
+
+ // TODO: Investigate using GetExprRange() to get tighter bounds
+ // on the bit ranges.
+ QualType OtherT = Other->IgnoreParenImpCasts()->getType();
+ if (const auto *AT = OtherT->getAs<AtomicType>())
+ OtherT = AT->getValueType();
+
+ IntRange OtherRange = IntRange::forValueOfType(S.Context, OtherT);
+
+ if (llvm::APSInt::isSameValue(
+ llvm::APSInt::getMaxValue(OtherRange.Width,
+ OtherT->isUnsignedIntegerType()),
+ Value))
+ return LimitType::Max;
+
+ if (llvm::APSInt::isSameValue(
+ llvm::APSInt::getMinValue(OtherRange.Width,
+ OtherT->isUnsignedIntegerType()),
+ Value))
+ return LimitType::Min;
+
+ return llvm::Optional<LimitType>();
}
bool HasEnumType(Expr *E) {
@@ -8583,63 +8635,60 @@
return E->getType()->isEnumeralType();
}
-bool isNonBooleanUnsignedValue(Expr *E) {
- // We are checking that the expression is not known to have boolean value,
- // is an integer type; and is either unsigned after implicit casts,
- // or was unsigned before implicit casts.
- return !E->isKnownToHaveBooleanValue() && E->getType()->isIntegerType() &&
- (!E->getType()->isSignedIntegerType() ||
- !E->IgnoreParenImpCasts()->getType()->isSignedIntegerType());
-}
-
-bool CheckTautologicalComparisonWithZero(Sema &S, BinaryOperator *E) {
- // Disable warning in template instantiations.
- if (S.inTemplateInstantiation())
+bool CheckTautologicalComparison(Sema &S, BinaryOperator *E, Expr *Constant,
+ Expr *Other, const llvm::APSInt &Value,
+ bool RhsConstant) {
+ // Disable warning in template instantiations
+ // and only analyze <, >, <= and >= operations.
+ if (S.inTemplateInstantiation() || !E->isRelationalOp())
return false;
- // bool values are handled by DiagnoseOutOfRangeComparison().
-
BinaryOperatorKind Op = E->getOpcode();
- if (E->isValueDependent())
+
+ QualType OType = Other->IgnoreParenImpCasts()->getType();
+
+ llvm::Optional<LimitType> ValueType; // Which limit (min/max) is the constant?
+
+ if (!(isNonBooleanIntegerValue(Other) &&
+ (ValueType = IsTypeLimit(S, Constant, Other, Value))))
return false;
- Expr *LHS = E->getLHS();
- Expr *RHS = E->getRHS();
+ bool ConstIsLowerBound = (Op == BO_LT || Op == BO_LE) ^ RhsConstant;
+ bool ResultWhenConstEqualsOther = (Op == BO_LE || Op == BO_GE);
+ bool ResultWhenConstNeOther =
+ ConstIsLowerBound ^ (ValueType == LimitType::Max);
+ if (ResultWhenConstEqualsOther != ResultWhenConstNeOther)
+ return false; // The comparison is not tautological.
- bool Match = true;
+ const bool Result = ResultWhenConstEqualsOther;
- if (Op == BO_LT && isNonBooleanUnsignedValue(LHS) && IsZero(S, RHS)) {
- S.Diag(E->getOperatorLoc(),
- HasEnumType(LHS) ? diag::warn_lunsigned_enum_always_true_comparison
- : diag::warn_lunsigned_always_true_comparison)
- << "< 0" << false << LHS->getSourceRange() << RHS->getSourceRange();
- } else if (Op == BO_GE && isNonBooleanUnsignedValue(LHS) && IsZero(S, RHS)) {
- S.Diag(E->getOperatorLoc(),
- HasEnumType(LHS) ? diag::warn_lunsigned_enum_always_true_comparison
- : diag::warn_lunsigned_always_true_comparison)
- << ">= 0" << true << LHS->getSourceRange() << RHS->getSourceRange();
- } else if (Op == BO_GT && isNonBooleanUnsignedValue(RHS) && IsZero(S, LHS)) {
- S.Diag(E->getOperatorLoc(),
- HasEnumType(RHS) ? diag::warn_runsigned_enum_always_true_comparison
- : diag::warn_runsigned_always_true_comparison)
- << "0 >" << false << LHS->getSourceRange() << RHS->getSourceRange();
- } else if (Op == BO_LE && isNonBooleanUnsignedValue(RHS) && IsZero(S, LHS)) {
- S.Diag(E->getOperatorLoc(),
- HasEnumType(RHS) ? diag::warn_runsigned_enum_always_true_comparison
- : diag::warn_runsigned_always_true_comparison)
- << "0 <=" << true << LHS->getSourceRange() << RHS->getSourceRange();
- } else
- Match = false;
+ unsigned Diag = (isNonBooleanUnsignedValue(Other) && Value == 0)
+ ? (HasEnumType(Other)
+ ? diag::warn_unsigned_enum_always_true_comparison
+ : diag::warn_unsigned_always_true_comparison)
+ : diag::warn_tautological_constant_compare;
- return Match;
+ // Should be enough for uint128 (39 decimal digits)
+ SmallString<64> PrettySourceValue;
+ llvm::raw_svector_ostream OS(PrettySourceValue);
+ OS << Value;
+
+ S.Diag(E->getOperatorLoc(), Diag)
+ << RhsConstant << OType << E->getOpcodeStr() << OS.str() << Result
+ << E->getLHS()->getSourceRange() << E->getRHS()->getSourceRange();
+
+ return true;
}
-void DiagnoseOutOfRangeComparison(Sema &S, BinaryOperator *E, Expr *Constant,
+bool DiagnoseOutOfRangeComparison(Sema &S, BinaryOperator *E, Expr *Constant,
Expr *Other, const llvm::APSInt &Value,
bool RhsConstant) {
// Disable warning in template instantiations.
if (S.inTemplateInstantiation())
- return;
+ return false;
+
+ Constant = Constant->IgnoreParenImpCasts();
+ Other = Other->IgnoreParenImpCasts();
// TODO: Investigate using GetExprRange() to get tighter bounds
// on the bit ranges.
@@ -8651,10 +8700,6 @@
bool OtherIsBooleanType = Other->isKnownToHaveBooleanValue();
- // 0 values are handled later by CheckTautologicalComparisonWithZero().
- if ((Value == 0) && (!OtherIsBooleanType))
- return;
-
BinaryOperatorKind op = E->getOpcode();
bool IsTrue = true;
@@ -8670,7 +8715,7 @@
QualType CommonT = E->getLHS()->getType();
if (S.Context.hasSameUnqualifiedType(OtherT, ConstantT))
- return;
+ return false;
assert((OtherT->isIntegerType() && ConstantT->isIntegerType()) &&
"comparison with non-integer type");
@@ -8685,38 +8730,38 @@
// Check that the constant is representable in type OtherT.
if (ConstantSigned) {
if (OtherWidth >= Value.getMinSignedBits())
- return;
+ return false;
} else { // !ConstantSigned
if (OtherWidth >= Value.getActiveBits() + 1)
- return;
+ return false;
}
} else { // !OtherSigned
// Check that the constant is representable in type OtherT.
// Negative values are out of range.
if (ConstantSigned) {
if (Value.isNonNegative() && OtherWidth >= Value.getActiveBits())
- return;
+ return false;
} else { // !ConstantSigned
if (OtherWidth >= Value.getActiveBits())
- return;
+ return false;
}
}
} else { // !CommonSigned
if (OtherRange.NonNegative) {
if (OtherWidth >= Value.getActiveBits())
- return;
+ return false;
} else { // OtherSigned
assert(!ConstantSigned &&
"Two signed types converted to unsigned types.");
// Check to see if the constant is representable in OtherT.
if (OtherWidth > Value.getActiveBits())
- return;
+ return false;
// Check to see if the constant is equivalent to a negative value
// cast to CommonT.
if (S.Context.getIntWidth(ConstantT) ==
S.Context.getIntWidth(CommonT) &&
Value.isNegative() && Value.getMinSignedBits() <= OtherWidth)
- return;
+ return false;
// The constant value rests between values that OtherT can represent
// after conversion. Relational comparison still works, but equality
// comparisons will be tautological.
@@ -8729,7 +8774,7 @@
if (op == BO_EQ || op == BO_NE) {
IsTrue = op == BO_NE;
} else if (EqualityOnly) {
- return;
+ return false;
} else if (RhsConstant) {
if (op == BO_GT || op == BO_GE)
IsTrue = !PositiveConstant;
@@ -8817,7 +8862,7 @@
} else if (CmpRes == ATrue) {
IsTrue = true;
} else {
- return;
+ return false;
}
}
@@ -8840,6 +8885,8 @@
<< OS.str() << LiteralOrBoolConstant
<< OtherT << (OtherIsBooleanType && !OtherT->isBooleanType()) << IsTrue
<< E->getLHS()->getSourceRange() << E->getRHS()->getSourceRange());
+
+ return true;
}
/// Analyze the operands of the given comparison. Implements the
@@ -8865,44 +8912,48 @@
if (E->isValueDependent())
return AnalyzeImpConvsInComparison(S, E);
- Expr *LHS = E->getLHS()->IgnoreParenImpCasts();
- Expr *RHS = E->getRHS()->IgnoreParenImpCasts();
-
- bool IsComparisonConstant = false;
-
- // Check whether an integer constant comparison results in a value
- // of 'true' or 'false'.
+ Expr *LHS = E->getLHS();
+ Expr *RHS = E->getRHS();
+
if (T->isIntegralType(S.Context)) {
llvm::APSInt RHSValue;
- bool IsRHSIntegralLiteral =
- RHS->isIntegerConstantExpr(RHSValue, S.Context);
llvm::APSInt LHSValue;
- bool IsLHSIntegralLiteral =
- LHS->isIntegerConstantExpr(LHSValue, S.Context);
- if (IsRHSIntegralLiteral && !IsLHSIntegralLiteral)
- DiagnoseOutOfRangeComparison(S, E, RHS, LHS, RHSValue, true);
- else if (!IsRHSIntegralLiteral && IsLHSIntegralLiteral)
- DiagnoseOutOfRangeComparison(S, E, LHS, RHS, LHSValue, false);
- else
- IsComparisonConstant =
- (IsRHSIntegralLiteral && IsLHSIntegralLiteral);
- } else if (!T->hasUnsignedIntegerRepresentation())
- IsComparisonConstant = E->isIntegerConstantExpr(S.Context);
- // We don't care about value-dependent expressions or expressions
- // whose result is a constant.
- if (IsComparisonConstant)
- return AnalyzeImpConvsInComparison(S, E);
+ bool IsRHSIntegralLiteral = RHS->isIntegerConstantExpr(RHSValue, S.Context);
+ bool IsLHSIntegralLiteral = LHS->isIntegerConstantExpr(LHSValue, S.Context);
- // If this is a tautological comparison, suppress -Wsign-compare.
- if (CheckTautologicalComparisonWithZero(S, E))
- return AnalyzeImpConvsInComparison(S, E);
+ // We don't care about expressions whose result is a constant.
+ if (IsRHSIntegralLiteral && IsLHSIntegralLiteral)
+ return AnalyzeImpConvsInComparison(S, E);
- // We don't do anything special if this isn't an unsigned integral
- // comparison: we're only interested in integral comparisons, and
- // signed comparisons only happen in cases we don't care to warn about.
- if (!T->hasUnsignedIntegerRepresentation())
+ // We only care about expressions where just one side is literal
+ if (IsRHSIntegralLiteral ^ IsLHSIntegralLiteral) {
+ // Is the constant on the RHS or LHS?
+ const bool RhsConstant = IsRHSIntegralLiteral;
+ Expr *Const = RhsConstant ? RHS : LHS;
+ Expr *Other = RhsConstant ? LHS : RHS;
+ const llvm::APSInt &Value = RhsConstant ? RHSValue : LHSValue;
+
+ // Check whether an integer constant comparison results in a value
+ // of 'true' or 'false'.
+
+ if (CheckTautologicalComparison(S, E, Const, Other, Value, RhsConstant))
+ return AnalyzeImpConvsInComparison(S, E);
+
+ if (DiagnoseOutOfRangeComparison(S, E, Const, Other, Value, RhsConstant))
+ return AnalyzeImpConvsInComparison(S, E);
+ }
+ }
+
+ if (!T->hasUnsignedIntegerRepresentation()) {
+ // We don't do anything special if this isn't an unsigned integral
+ // comparison: we're only interested in integral comparisons, and
+ // signed comparisons only happen in cases we don't care to warn about.
return AnalyzeImpConvsInComparison(S, E);
+ }
+
+ LHS = LHS->IgnoreParenImpCasts();
+ RHS = RHS->IgnoreParenImpCasts();
// Check to see if one of the (unmodified) operands is of different
// signedness.