diff options
| -rw-r--r-- | lib/Sema/SemaExpr.cpp | 44 | ||||
| -rw-r--r-- | test/Sema/compare.c | 3 |
2 files changed, 27 insertions, 20 deletions
diff --git a/lib/Sema/SemaExpr.cpp b/lib/Sema/SemaExpr.cpp index a8be333967..121ed6a8ab 100644 --- a/lib/Sema/SemaExpr.cpp +++ b/lib/Sema/SemaExpr.cpp @@ -5110,6 +5110,22 @@ QualType Sema::CheckShiftOperands(Expr *&lex, Expr *&rex, SourceLocation Loc, return LHSTy; } +/// Returns true if we can prove that the result of the given +/// integral expression will not have its sign bit set. +static bool IsSignBitProvablyZero(ASTContext &Context, Expr *E) { + E = E->IgnoreParens(); + + llvm::APSInt value; + if (E->isIntegerConstantExpr(value, Context)) + return value.isNonNegative(); + + if (ConditionalOperator *CO = dyn_cast<ConditionalOperator>(E)) + return IsSignBitProvablyZero(Context, CO->getLHS()) && + IsSignBitProvablyZero(Context, CO->getRHS()); + + return false; +} + /// \brief Implements -Wsign-compare. /// /// \param lex the left-hand expression @@ -5157,27 +5173,15 @@ void Sema::CheckSignCompare(Expr *lex, Expr *rex, SourceLocation OpLoc, // If the value is a non-negative integer constant, then the // signed->unsigned conversion won't change it. - llvm::APSInt value; - if (signedOperand->isIntegerConstantExpr(value, Context)) { - assert(value.isSigned() && "result of signed expression not signed"); - - if (value.isNonNegative()) - return; - } - - if (Equality) { - // For (in)equality comparisons, if the unsigned operand is a - // constant which cannot collide with a overflowed signed operand, - // then reinterpreting the signed operand as unsigned will not - // change the result of the comparison. - if (unsignedOperand->isIntegerConstantExpr(value, Context)) { - assert(!value.isSigned() && "result of unsigned expression is signed"); + if (IsSignBitProvablyZero(Context, signedOperand)) + return; - // 2's complement: test the top bit. - if (value.isNonNegative()) - return; - } - } + // For (in)equality comparisons, if the unsigned operand is a + // constant which cannot collide with a overflowed signed operand, + // then reinterpreting the signed operand as unsigned will not + // change the result of the comparison. + if (Equality && IsSignBitProvablyZero(Context, unsignedOperand)) + return; Diag(OpLoc, PD) << lex->getType() << rex->getType() diff --git a/test/Sema/compare.c b/test/Sema/compare.c index 75a3cf1f62..bacd47e33c 100644 --- a/test/Sema/compare.c +++ b/test/Sema/compare.c @@ -194,6 +194,9 @@ int ints(long a, unsigned long b) { ((short) a < (unsigned short) 0x80000) + // expected-warning {{comparison of integers of different signs}} ((signed char) a < (unsigned char) 0x80000) + // expected-warning {{comparison of integers of different signs}} + // We should be able to avoid warning about this. + (b != (a < 4 ? 1 : 2)) + + 10 ; } |