On Fri, Sep 8, 2017 at 3:26 PM, Roman Lebedev <lebedev...@gmail.com> wrote: > On Fri, Sep 8, 2017 at 2:48 PM, Sam McCall <sammcc...@google.com> wrote: > Hi. > >> Nice fix! > Thank you! > >> It catches a lot of new cases on our codebase, all technically >> correct so far. >> >> A couple of issues though: >> A) Rollout - until we've completely cleaned up, we need to disable >> -Wtautological-compare entirely, which is a valuable check. I imagine anyone >> else using -Werror is in the same boat. >> What do you think about putting the new warnings behind a subcategory? (e.g. >> -Wtautological-compare-unsigned-zero, implied by -Wtautological-compare) >> It's an ugly artifact of the history here, but allows this fix to be rolled >> out in a controlled way. > https://reviews.llvm.org/D37620 And landed.
>> B) Enums (not new I guess). Typical case: if (enum < 0 || enum > MAX) >> The warning strongly suggests that the enum < 0 check has no effect (for >> enums with nonnegative ranges). >> Clang doesn't seem to optimize such checks out though, and they seem likely >> to catch bugs in some cases. Yes, only if there's UB elsewhere, but I assume >> not optimizing out these checks indicates a deliberate decision to stay >> somewhat compatible with a technically-incorrect mental model. >> If this is the case, should we move these to a -Wtautological-compare-enum >> subcategory? > (Did not look at this yet) https://reviews.llvm.org/D37629 i hope that is what you meant. > Roman. Roman. >> On Fri, Sep 8, 2017 at 12:14 AM, Roman Lebedev via cfe-commits >> <cfe-commits@lists.llvm.org> wrote: >>> >>> Author: lebedevri >>> Date: Thu Sep 7 15:14:25 2017 >>> New Revision: 312750 >>> >>> URL: http://llvm.org/viewvc/llvm-project?rev=312750&view=rev >>> Log: >>> [Sema] -Wtautological-compare: handle comparison of unsigned with 0S. >>> >>> Summary: >>> This is a first half(?) of a fix for the following bug: >>> https://bugs.llvm.org/show_bug.cgi?id=34147 (gcc -Wtype-limits) >>> >>> GCC's -Wtype-limits does warn on comparison of unsigned value >>> with signed zero (as in, with 0), but clang only warns if the >>> zero is unsigned (i.e. 0U). >>> >>> Also, be careful not to double-warn, or falsely warn on >>> comparison of signed/fp variable and signed 0. >>> >>> Yes, all these testcases are needed. >>> >>> Testing: $ ninja check-clang-sema check-clang-semacxx >>> Also, no new warnings for clang stage-2 build. >>> >>> Reviewers: rjmccall, rsmith, aaron.ballman >>> >>> Reviewed By: rjmccall >>> >>> Subscribers: cfe-commits >>> >>> Tags: #clang >>> >>> Differential Revision: https://reviews.llvm.org/D37565 >>> >>> Modified: >>> cfe/trunk/docs/ReleaseNotes.rst >>> cfe/trunk/lib/Sema/SemaChecking.cpp >>> cfe/trunk/test/Sema/compare.c >>> cfe/trunk/test/Sema/outof-range-constant-compare.c >>> cfe/trunk/test/SemaCXX/compare.cpp >>> >>> Modified: cfe/trunk/docs/ReleaseNotes.rst >>> URL: >>> http://llvm.org/viewvc/llvm-project/cfe/trunk/docs/ReleaseNotes.rst?rev=312750&r1=312749&r2=312750&view=diff >>> >>> ============================================================================== >>> --- cfe/trunk/docs/ReleaseNotes.rst (original) >>> +++ cfe/trunk/docs/ReleaseNotes.rst Thu Sep 7 15:14:25 2017 >>> @@ -71,6 +71,13 @@ Improvements to Clang's diagnostics >>> errors/warnings, as the system frameworks might add a method with the >>> same >>> selector which could make the message send to ``id`` ambiguous. >>> >>> +- ``-Wtautological-compare`` now warns when comparing an unsigned integer >>> and 0 >>> + regardless of whether the constant is signed or unsigned." >>> + >>> +- ``-Wtautological-compare`` now warns about comparing a signed integer >>> and 0 >>> + when the signed integer is coerced to an unsigned type for the >>> comparison. >>> + ``-Wsign-compare`` was adjusted not to warn in this case. >>> + >>> Non-comprehensive list of changes in this release >>> ------------------------------------------------- >>> >>> >>> Modified: cfe/trunk/lib/Sema/SemaChecking.cpp >>> URL: >>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaChecking.cpp?rev=312750&r1=312749&r2=312750&view=diff >>> >>> ============================================================================== >>> --- cfe/trunk/lib/Sema/SemaChecking.cpp (original) >>> +++ cfe/trunk/lib/Sema/SemaChecking.cpp Thu Sep 7 15:14:25 2017 >>> @@ -8567,32 +8567,51 @@ bool HasEnumType(Expr *E) { >>> return E->getType()->isEnumeralType(); >>> } >>> >>> -void CheckTrivialUnsignedComparison(Sema &S, BinaryOperator *E) { >>> +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()) >>> - return; >>> + return false; >>> + >>> + // bool values are handled by DiagnoseOutOfRangeComparison(). >>> >>> BinaryOperatorKind op = E->getOpcode(); >>> if (E->isValueDependent()) >>> - return; >>> + return false; >>> >>> - if (op == BO_LT && IsZero(S, E->getRHS())) { >>> + Expr *LHS = E->getLHS(); >>> + Expr *RHS = E->getRHS(); >>> + >>> + bool Match = true; >>> + >>> + if (op == BO_LT && isNonBooleanUnsignedValue(LHS) && IsZero(S, RHS)) { >>> S.Diag(E->getOperatorLoc(), >>> diag::warn_lunsigned_always_true_comparison) >>> - << "< 0" << "false" << HasEnumType(E->getLHS()) >>> - << E->getLHS()->getSourceRange() << E->getRHS()->getSourceRange(); >>> - } else if (op == BO_GE && IsZero(S, E->getRHS())) { >>> + << "< 0" << "false" << HasEnumType(LHS) >>> + << LHS->getSourceRange() << RHS->getSourceRange(); >>> + } else if (op == BO_GE && isNonBooleanUnsignedValue(LHS) && IsZero(S, >>> RHS)) { >>> S.Diag(E->getOperatorLoc(), >>> diag::warn_lunsigned_always_true_comparison) >>> - << ">= 0" << "true" << HasEnumType(E->getLHS()) >>> - << E->getLHS()->getSourceRange() << E->getRHS()->getSourceRange(); >>> - } else if (op == BO_GT && IsZero(S, E->getLHS())) { >>> + << ">= 0" << "true" << HasEnumType(LHS) >>> + << LHS->getSourceRange() << RHS->getSourceRange(); >>> + } else if (op == BO_GT && isNonBooleanUnsignedValue(RHS) && IsZero(S, >>> LHS)) { >>> S.Diag(E->getOperatorLoc(), >>> diag::warn_runsigned_always_true_comparison) >>> - << "0 >" << "false" << HasEnumType(E->getRHS()) >>> - << E->getLHS()->getSourceRange() << E->getRHS()->getSourceRange(); >>> - } else if (op == BO_LE && IsZero(S, E->getLHS())) { >>> + << "0 >" << "false" << HasEnumType(RHS) >>> + << LHS->getSourceRange() << RHS->getSourceRange(); >>> + } else if (op == BO_LE && isNonBooleanUnsignedValue(RHS) && IsZero(S, >>> LHS)) { >>> S.Diag(E->getOperatorLoc(), >>> diag::warn_runsigned_always_true_comparison) >>> - << "0 <=" << "true" << HasEnumType(E->getRHS()) >>> - << E->getLHS()->getSourceRange() << E->getRHS()->getSourceRange(); >>> - } >>> + << "0 <=" << "true" << HasEnumType(RHS) >>> + << LHS->getSourceRange() << RHS->getSourceRange(); >>> + } else >>> + Match = false; >>> + >>> + return Match; >>> } >>> >>> void DiagnoseOutOfRangeComparison(Sema &S, BinaryOperator *E, Expr >>> *Constant, >>> @@ -8612,7 +8631,7 @@ void DiagnoseOutOfRangeComparison(Sema & >>> >>> bool OtherIsBooleanType = Other->isKnownToHaveBooleanValue(); >>> >>> - // 0 values are handled later by CheckTrivialUnsignedComparison(). >>> + // 0 values are handled later by CheckTautologicalComparisonWithZero(). >>> if ((Value == 0) && (!OtherIsBooleanType)) >>> return; >>> >>> @@ -8849,16 +8868,22 @@ void AnalyzeComparison(Sema &S, BinaryOp >>> (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); >>> + >>> + // If this is a tautological comparison, suppress -Wsign-compare. >>> + if (CheckTautologicalComparisonWithZero(S, E)) >>> + 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. >>> - // >>> - // We also don't care about value-dependent expressions or expressions >>> - // whose result is a constant. >>> - if (!T->hasUnsignedIntegerRepresentation() || IsComparisonConstant) >>> + if (!T->hasUnsignedIntegerRepresentation()) >>> return AnalyzeImpConvsInComparison(S, E); >>> - >>> + >>> // Check to see if one of the (unmodified) operands is of different >>> // signedness. >>> Expr *signedOperand, *unsignedOperand; >>> @@ -8871,7 +8896,6 @@ void AnalyzeComparison(Sema &S, BinaryOp >>> signedOperand = RHS; >>> unsignedOperand = LHS; >>> } else { >>> - CheckTrivialUnsignedComparison(S, E); >>> return AnalyzeImpConvsInComparison(S, E); >>> } >>> >>> @@ -8883,11 +8907,9 @@ void AnalyzeComparison(Sema &S, BinaryOp >>> AnalyzeImplicitConversions(S, LHS, E->getOperatorLoc()); >>> AnalyzeImplicitConversions(S, RHS, E->getOperatorLoc()); >>> >>> - // If the signed range is non-negative, -Wsign-compare won't fire, >>> - // but we should still check for comparisons which are always true >>> - // or false. >>> + // If the signed range is non-negative, -Wsign-compare won't fire. >>> if (signedRange.NonNegative) >>> - return CheckTrivialUnsignedComparison(S, E); >>> + return; >>> >>> // For (in)equality comparisons, if the unsigned operand is a >>> // constant which cannot collide with a overflowed signed operand, >>> >>> Modified: cfe/trunk/test/Sema/compare.c >>> URL: >>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/compare.c?rev=312750&r1=312749&r2=312750&view=diff >>> >>> ============================================================================== >>> --- cfe/trunk/test/Sema/compare.c (original) >>> +++ cfe/trunk/test/Sema/compare.c Thu Sep 7 15:14:25 2017 >>> @@ -77,7 +77,7 @@ int ints(long a, unsigned long b) { >>> ((int) a == (unsigned int) B) + >>> ((short) a == (unsigned short) B) + >>> ((signed char) a == (unsigned char) B) + >>> - (a < (unsigned long) B) + // expected-warning {{comparison of >>> integers of different signs}} >>> + (a < (unsigned long) B) + // expected-warning {{comparison of >>> unsigned expression < 0 is always false}} >>> (a < (unsigned int) B) + >>> (a < (unsigned short) B) + >>> (a < (unsigned char) B) + >>> @@ -85,8 +85,8 @@ int ints(long a, unsigned long b) { >>> ((int) a < B) + >>> ((short) a < B) + >>> ((signed char) a < B) + >>> - ((long) a < (unsigned long) B) + // expected-warning >>> {{comparison of integers of different signs}} >>> - ((int) a < (unsigned int) B) + // expected-warning {{comparison >>> of integers of different signs}} >>> + ((long) a < (unsigned long) B) + // expected-warning >>> {{comparison of unsigned expression < 0 is always false}} >>> + ((int) a < (unsigned int) B) + // expected-warning {{comparison >>> of unsigned expression < 0 is always false}} >>> ((short) a < (unsigned short) B) + >>> ((signed char) a < (unsigned char) B) + >>> >>> >>> Modified: cfe/trunk/test/Sema/outof-range-constant-compare.c >>> URL: >>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/outof-range-constant-compare.c?rev=312750&r1=312749&r2=312750&view=diff >>> >>> ============================================================================== >>> --- cfe/trunk/test/Sema/outof-range-constant-compare.c (original) >>> +++ cfe/trunk/test/Sema/outof-range-constant-compare.c Thu Sep 7 15:14:25 >>> 2017 >>> @@ -6,6 +6,59 @@ int value(void); >>> int main() >>> { >>> int a = value(); >>> + >>> + if (a == 0x0000000000000000L) >>> + return 0; >>> + if (a != 0x0000000000000000L) >>> + return 0; >>> + if (a < 0x0000000000000000L) >>> + return 0; >>> + if (a <= 0x0000000000000000L) >>> + return 0; >>> + if (a > 0x0000000000000000L) >>> + return 0; >>> + if (a >= 0x0000000000000000L) >>> + return 0; >>> + >>> + if (0x0000000000000000L == a) >>> + return 0; >>> + if (0x0000000000000000L != a) >>> + return 0; >>> + if (0x0000000000000000L < a) >>> + return 0; >>> + if (0x0000000000000000L <= a) >>> + return 0; >>> + if (0x0000000000000000L > a) >>> + return 0; >>> + if (0x0000000000000000L >= a) >>> + return 0; >>> + >>> + if (a == 0x0000000000000000UL) >>> + return 0; >>> + if (a != 0x0000000000000000UL) >>> + return 0; >>> + if (a < 0x0000000000000000UL) // expected-warning {{comparison of >>> unsigned expression < 0 is always false}} >>> + return 0; >>> + if (a <= 0x0000000000000000UL) >>> + return 0; >>> + if (a > 0x0000000000000000UL) >>> + return 0; >>> + if (a >= 0x0000000000000000UL) // expected-warning {{comparison of >>> unsigned expression >= 0 is always true}} >>> + return 0; >>> + >>> + if (0x0000000000000000UL == a) >>> + return 0; >>> + if (0x0000000000000000UL != a) >>> + return 0; >>> + if (0x0000000000000000UL < a) >>> + return 0; >>> + if (0x0000000000000000UL <= a) // expected-warning {{comparison of 0 >>> <= unsigned expression is always true}} >>> + return 0; >>> + if (0x0000000000000000UL > a) // expected-warning {{comparison of 0 > >>> unsigned expression is always false}} >>> + return 0; >>> + if (0x0000000000000000UL >= a) >>> + return 0; >>> + >>> if (a == 0x1234567812345678L) // expected-warning {{comparison of >>> constant 1311768465173141112 with expression of type 'int' is always false}} >>> return 0; >>> if (a != 0x1234567812345678L) // expected-warning {{comparison of >>> constant 1311768465173141112 with expression of type 'int' is always true}} >>> @@ -74,6 +127,7 @@ int main() >>> return 0; >>> if (0x1234567812345678L >= s) // expected-warning {{comparison of >>> constant 1311768465173141112 with expression of type 'short' is always >>> true}} >>> return 0; >>> + >>> long l = value(); >>> if (l == 0x1234567812345678L) >>> return 0; >>> @@ -106,13 +160,13 @@ int main() >>> return 0; >>> if (un != 0x0000000000000000L) >>> return 0; >>> - if (un < 0x0000000000000000L) >>> + if (un < 0x0000000000000000L) // expected-warning {{comparison of >>> unsigned expression < 0 is always false}} >>> return 0; >>> if (un <= 0x0000000000000000L) >>> return 0; >>> if (un > 0x0000000000000000L) >>> return 0; >>> - if (un >= 0x0000000000000000L) >>> + if (un >= 0x0000000000000000L) // expected-warning {{comparison of >>> unsigned expression >= 0 is always true}} >>> return 0; >>> >>> if (0x0000000000000000L == un) >>> @@ -121,19 +175,92 @@ int main() >>> return 0; >>> if (0x0000000000000000L < un) >>> return 0; >>> - if (0x0000000000000000L <= un) >>> + if (0x0000000000000000L <= un) // expected-warning {{comparison of 0 >>> <= unsigned expression is always true}} >>> return 0; >>> - if (0x0000000000000000L > un) >>> + if (0x0000000000000000L > un) // expected-warning {{comparison of 0 > >>> unsigned expression is always false}} >>> return 0; >>> if (0x0000000000000000L >= un) >>> return 0; >>> + >>> + if (un == 0x0000000000000000UL) >>> + return 0; >>> + if (un != 0x0000000000000000UL) >>> + return 0; >>> + if (un < 0x0000000000000000UL) // expected-warning {{comparison of >>> unsigned expression < 0 is always false}} >>> + return 0; >>> + if (un <= 0x0000000000000000UL) >>> + return 0; >>> + if (un > 0x0000000000000000UL) >>> + return 0; >>> + if (un >= 0x0000000000000000UL) // expected-warning {{comparison of >>> unsigned expression >= 0 is always true}} >>> + return 0; >>> + >>> + if (0x0000000000000000UL == un) >>> + return 0; >>> + if (0x0000000000000000UL != un) >>> + return 0; >>> + if (0x0000000000000000UL < un) >>> + return 0; >>> + if (0x0000000000000000UL <= un) // expected-warning {{comparison of 0 >>> <= unsigned expression is always true}} >>> + return 0; >>> + if (0x0000000000000000UL > un) // expected-warning {{comparison of 0 >>> > unsigned expression is always false}} >>> + return 0; >>> + if (0x0000000000000000UL >= un) >>> + return 0; >>> + >>> float fl = 0; >>> - if (fl == 0x0000000000000000L) // no warning >>> - return 0; >>> + if (fl == 0x0000000000000000L) >>> + return 0; >>> + if (fl != 0x0000000000000000L) >>> + return 0; >>> + if (fl < 0x0000000000000000L) >>> + return 0; >>> + if (fl <= 0x0000000000000000L) >>> + return 0; >>> + if (fl > 0x0000000000000000L) >>> + return 0; >>> + if (fl >= 0x0000000000000000L) >>> + return 0; >>> >>> - float dl = 0; >>> - if (dl == 0x0000000000000000L) // no warning >>> - return 0; >>> + if (0x0000000000000000L == fl) >>> + return 0; >>> + if (0x0000000000000000L != fl) >>> + return 0; >>> + if (0x0000000000000000L < fl) >>> + return 0; >>> + if (0x0000000000000000L <= fl) >>> + return 0; >>> + if (0x0000000000000000L > fl) >>> + return 0; >>> + if (0x0000000000000000L >= fl) >>> + return 0; >>> + >>> + double dl = 0; >>> + if (dl == 0x0000000000000000L) >>> + return 0; >>> + if (dl != 0x0000000000000000L) >>> + return 0; >>> + if (dl < 0x0000000000000000L) >>> + return 0; >>> + if (dl <= 0x0000000000000000L) >>> + return 0; >>> + if (dl > 0x0000000000000000L) >>> + return 0; >>> + if (dl >= 0x0000000000000000L) >>> + return 0; >>> + >>> + if (0x0000000000000000L == dl) >>> + return 0; >>> + if (0x0000000000000000L != dl) >>> + return 0; >>> + if (0x0000000000000000L < dl) >>> + return 0; >>> + if (0x0000000000000000L <= dl) >>> + return 0; >>> + if (0x0000000000000000L > dl) >>> + return 0; >>> + if (0x0000000000000000L >= dl) >>> + return 0; >>> >>> enum E { >>> yes, >>> >>> Modified: cfe/trunk/test/SemaCXX/compare.cpp >>> URL: >>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/compare.cpp?rev=312750&r1=312749&r2=312750&view=diff >>> >>> ============================================================================== >>> --- cfe/trunk/test/SemaCXX/compare.cpp (original) >>> +++ cfe/trunk/test/SemaCXX/compare.cpp Thu Sep 7 15:14:25 2017 >>> @@ -73,7 +73,7 @@ int test0(long a, unsigned long b) { >>> ((int) a == (unsigned int) B) + >>> ((short) a == (unsigned short) B) + >>> ((signed char) a == (unsigned char) B) + >>> - (a < (unsigned long) B) + // expected-warning {{comparison of >>> integers of different signs}} >>> + (a < (unsigned long) B) + // expected-warning {{comparison of >>> unsigned expression < 0 is always false}} >>> (a < (unsigned int) B) + >>> (a < (unsigned short) B) + >>> (a < (unsigned char) B) + >>> @@ -81,8 +81,8 @@ int test0(long a, unsigned long b) { >>> ((int) a < B) + >>> ((short) a < B) + >>> ((signed char) a < B) + >>> - ((long) a < (unsigned long) B) + // expected-warning >>> {{comparison of integers of different signs}} >>> - ((int) a < (unsigned int) B) + // expected-warning {{comparison >>> of integers of different signs}} >>> + ((long) a < (unsigned long) B) + // expected-warning >>> {{comparison of unsigned expression < 0 is always false}} >>> + ((int) a < (unsigned int) B) + // expected-warning {{comparison >>> of unsigned expression < 0 is always false}} >>> ((short) a < (unsigned short) B) + >>> ((signed char) a < (unsigned char) B) + >>> >>> >>> >>> _______________________________________________ >>> cfe-commits mailing list >>> cfe-commits@lists.llvm.org >>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits >> >> _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
