Example:
% ./clang -Wshift-negative-value emit.c
emit.c:3:14: warning: shifting a negative signed value is undefined [-Wshift-negative-value]
int a = -1 << 3;
~~ ^
1 warning generated.
PR: 24026
Differential Revision: http://reviews.llvm.org/D10938
Reviewed by: rsmith
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@241478
91177308-0d34-0410-b5e6-
96231b3b80d8
InGroup<DivZero>;
def warn_remainder_by_zero : Warning<"remainder by zero is undefined">,
InGroup<DivZero>;
+def warn_shift_lhs_negative : Warning<"shifting a negative signed value is undefined">,
+ InGroup<DiagGroup<"shift-negative-value">>;
def warn_shift_negative : Warning<"shift count is negative">,
InGroup<DiagGroup<"shift-count-negative">>;
def warn_shift_gt_typewidth : Warning<"shift count >= width of type">,
// representable in the result type, so never warn for those.
llvm::APSInt Left;
if (LHS.get()->isValueDependent() ||
- !LHS.get()->isIntegerConstantExpr(Left, S.Context) ||
- LHSType->hasUnsignedIntegerRepresentation())
+ LHSType->hasUnsignedIntegerRepresentation() ||
+ !LHS.get()->EvaluateAsInt(Left, S.Context))
return;
+
+ // If LHS does not have a signed type and non-negative value
+ // then, the behavior is undefined. Warn about it.
+ if (Left.isNegative()) {
+ S.DiagRuntimeBehavior(Loc, LHS.get(),
+ S.PDiag(diag::warn_shift_lhs_negative)
+ << LHS.get()->getSourceRange());
+ return;
+ }
+
llvm::APInt ResultBits =
static_cast<llvm::APInt&>(Right) + Left.getMinSignedBits();
if (LeftBits.uge(ResultBits))
constexpr int shl_unsigned_negative = unsigned(-3) << 1; // ok
constexpr int shl_unsigned_into_sign = 1u << 31; // ok
constexpr int shl_unsigned_overflow = 1024u << 31; // ok
- constexpr int shl_signed_negative = (-3) << 1; // expected-error {{constant expression}} expected-note {{left shift of negative value -3}}
+ constexpr int shl_signed_negative = (-3) << 1; // expected-warning {{shifting a negative signed value is undefined}} // expected-error {{constant expression}} expected-note {{left shift of negative value -3}}
constexpr int shl_signed_ok = 1 << 30; // ok
constexpr int shl_signed_into_sign = 1 << 31; // ok (DR1457)
constexpr int shl_signed_into_sign_2 = 0x7fffffff << 1; // ok (DR1457)
i = 1 << (WORD_BIT - 2);
i = 2 << (WORD_BIT - 1); // expected-warning {{bits to represent, but 'int' only has}}
i = 1 << (WORD_BIT - 1); // expected-warning {{sets the sign bit of the shift expression}}
- i = -1 << (WORD_BIT - 1);
+ i = -1 << (WORD_BIT - 1); // expected-warning {{shifting a negative signed value is undefined}}
+ i = -1 << 0; // expected-warning {{shifting a negative signed value is undefined}}
i = 0 << (WORD_BIT - 1);
i = (char)1 << (WORD_BIT - 2);
u = 5U << (WORD_BIT - 1);
long long int lli;
- lli = INT_MIN << 2; // expected-warning {{bits to represent, but 'int' only has}}
+ lli = INT_MIN << 2; // expected-warning {{shifting a negative signed value is undefined}}
lli = 1LL << (sizeof(long long) * CHAR_BIT - 2);
}