Author: Malavika Samak Date: 2025-05-16T18:33:51-07:00 New Revision: 39315663a40a261772df94218fd33e205e888e54
URL: https://github.com/llvm/llvm-project/commit/39315663a40a261772df94218fd33e205e888e54 DIFF: https://github.com/llvm/llvm-project/commit/39315663a40a261772df94218fd33e205e888e54.diff LOG: [-Wunsafe-buffer-usage] Fix false warnings when const sized array is safely accessed (array [idx %const]) (#140113) The -Wunsafe-buffer-usage analysis currently warns when a const sized array is safely accessed, with an index that is bound by the remainder operator. The false alarm is now suppressed. Example: int circular_buffer(int array[10], uint idx) { return array[idx %10]; // Safe operation } rdar://148443453 --------- Co-authored-by: MalavikaSamak <malavi...@apple.com> Added: Modified: clang/lib/Analysis/UnsafeBufferUsage.cpp clang/test/SemaCXX/warn-unsafe-buffer-usage-array.cpp Removed: ################################################################################ diff --git a/clang/lib/Analysis/UnsafeBufferUsage.cpp b/clang/lib/Analysis/UnsafeBufferUsage.cpp index 5b72382ca9772..ec648e1a17af9 100644 --- a/clang/lib/Analysis/UnsafeBufferUsage.cpp +++ b/clang/lib/Analysis/UnsafeBufferUsage.cpp @@ -600,12 +600,27 @@ static bool isSafeArraySubscript(const ArraySubscriptExpr &Node, } else if (const auto *BE = dyn_cast<BinaryOperator>(IndexExpr)) { // For an integer expression `e` and an integer constant `n`, `e & n` and // `n & e` are bounded by `n`: - if (BE->getOpcode() != BO_And) + if (BE->getOpcode() != BO_And && BE->getOpcode() != BO_Rem) return false; const Expr *LHS = BE->getLHS(); const Expr *RHS = BE->getRHS(); + if (BE->getOpcode() == BO_Rem) { + // If n is a negative number, then n % const can be greater than const + if (!LHS->getType()->isUnsignedIntegerType()) { + return false; + } + + if (!RHS->isValueDependent() && RHS->EvaluateAsInt(EVResult, Ctx)) { + llvm::APSInt result = EVResult.Val.getInt(); + if (result.isNonNegative() && result.getLimitedValue() <= limit) + return true; + } + + return false; + } + if ((!LHS->isValueDependent() && LHS->EvaluateAsInt(EVResult, Ctx)) || // case: `n & e` (!RHS->isValueDependent() && diff --git a/clang/test/SemaCXX/warn-unsafe-buffer-usage-array.cpp b/clang/test/SemaCXX/warn-unsafe-buffer-usage-array.cpp index 3233999ea8ea2..00daa28b433eb 100644 --- a/clang/test/SemaCXX/warn-unsafe-buffer-usage-array.cpp +++ b/clang/test/SemaCXX/warn-unsafe-buffer-usage-array.cpp @@ -35,7 +35,21 @@ void constant_idx_safe0(unsigned idx) { buffer[0] = 0; } -int array[10]; // expected-warning {{'array' is an unsafe buffer that does not perform bounds checks}} +int array[10]; // expected-warning 3{{'array' is an unsafe buffer that does not perform bounds checks}} + +void circular_access_unsigned(unsigned idx) { + array[idx % 10]; + array[idx % 11]; // expected-note {{used in buffer access here}} + array[(idx + 3) % 10]; + array[(--idx) % 8]; + array[idx & 9 % 10]; + array[9 & idx % 11]; + array [12 % 10]; +} + +void circular_access_signed(int idx) { + array[idx % 10]; // expected-note {{used in buffer access here}} +} void masked_idx1(unsigned long long idx, Foo f) { // Bitwise and operation _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
