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[Sema] Fixed faulty shift count warning #69521

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Merged
merged 1 commit into from
Oct 25, 2023
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[Sema] Fixed faulty shift count warning #69521

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3 changes: 3 additions & 0 deletions clang/docs/ReleaseNotes.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -488,6 +488,9 @@ Bug Fixes in This Version
- Clang no longer permits using the `_BitInt` types as an underlying type for an
enumeration as specified in the C23 Standard.
Fixes (`#69619 <https://github.com/llvm/llvm-project/issues/69619>`_)
- Fixed an issue when a shift count specified by a small constant ``_BitInt()``,
in a left shift operation, could result in a faulty warnings about
``shift count >= width of type``.
- Clang now accepts anonymous members initialized with designated initializers
inside templates.
Fixes (`#65143 <https://github.com/llvm/llvm-project/issues/65143>`_)
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7 changes: 3 additions & 4 deletions clang/lib/Sema/SemaExpr.cpp
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Expand Up @@ -12143,8 +12143,7 @@ static void DiagnoseBadShiftValues(Sema& S, ExprResult &LHS, ExprResult &RHS,
auto FXSema = S.Context.getFixedPointSemantics(LHSExprType);
LeftSize = FXSema.getWidth() - (unsigned)FXSema.hasUnsignedPadding();
}
llvm::APInt LeftBits(Right.getBitWidth(), LeftSize);
if (Right.uge(LeftBits)) {
if (Right.uge(LeftSize)) {
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I feel like LeftSizeInBits would be a more appropriate name but the changes looks right.

S.DiagRuntimeBehavior(Loc, RHS.get(),
S.PDiag(diag::warn_shift_gt_typewidth)
<< RHS.get()->getSourceRange());
Expand Down Expand Up @@ -12186,7 +12185,7 @@ static void DiagnoseBadShiftValues(Sema& S, ExprResult &LHS, ExprResult &RHS,

llvm::APInt ResultBits =
static_cast<llvm::APInt &>(Right) + Left.getSignificantBits();
if (LeftBits.uge(ResultBits))
if (ResultBits.ule(LeftSize))
return;
llvm::APSInt Result = Left.extend(ResultBits.getLimitedValue());
Result = Result.shl(Right);
Expand All @@ -12200,7 +12199,7 @@ static void DiagnoseBadShiftValues(Sema& S, ExprResult &LHS, ExprResult &RHS,
// bugs -- if the result is cast back to an unsigned type, it will have the
// expected value. Thus we place this behind a different warning that can be
// turned off separately if needed.
if (LeftBits == ResultBits - 1) {
if (ResultBits - 1 == LeftSize) {
S.Diag(Loc, diag::warn_shift_result_sets_sign_bit)
<< HexResult << LHSType
<< LHS.get()->getSourceRange() << RHS.get()->getSourceRange();
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12 changes: 12 additions & 0 deletions clang/test/Sema/c2x-expr-range.c
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Expand Up @@ -12,3 +12,15 @@ void test1(int *a) {
void test2(__uint128_t *a) {
(void)(*a >> ((__uint128_t)__UINT64_MAX__ + 1) <= 0); // expected-warning {{shift count >= width of type}}
}

// Regression test for bug where a faulty warning was given. We don't expect to
// see any warning in this case.
_BitInt(128) test3(_BitInt(128) a) {
return a << 12wb;
}

// Similar to test3 above, but with a too large shift count. We expect to see a
// warning in this case.
_BitInt(128) test4(_BitInt(128) a) {
return a << 129wb; // expected-warning {{shift count >= width of type}}
}