From 24e2afed6df6cc064d5fa3d6d95f60cc6e614eb3 Mon Sep 17 00:00:00 2001 From: Karl-Johan Karlsson Date: Wed, 18 Oct 2023 16:40:53 +0200 Subject: [PATCH] [Sema] Fixed faulty shift count warning Constant values of _BitInt have the bitwith to exactly fit the constant number. This patch fix a problem in Sema when building an APInt where the supplied bitwidth can become too small and simply truncate the value leading to a faulty warning. --- clang/lib/Sema/SemaExpr.cpp | 7 +++---- clang/test/Sema/c2x-expr-range.c | 12 ++++++++++++ 2 files changed, 15 insertions(+), 4 deletions(-) diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp index aa30a3a0388755..c00178ee1835e0 100644 --- a/clang/lib/Sema/SemaExpr.cpp +++ b/clang/lib/Sema/SemaExpr.cpp @@ -12120,8 +12120,7 @@ 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)) { S.DiagRuntimeBehavior(Loc, RHS.get(), S.PDiag(diag::warn_shift_gt_typewidth) << RHS.get()->getSourceRange()); @@ -12163,7 +12162,7 @@ static void DiagnoseBadShiftValues(Sema& S, ExprResult &LHS, ExprResult &RHS, llvm::APInt ResultBits = static_cast(Right) + Left.getSignificantBits(); - if (LeftBits.uge(ResultBits)) + if (ResultBits.ule(LeftSize)) return; llvm::APSInt Result = Left.extend(ResultBits.getLimitedValue()); Result = Result.shl(Right); @@ -12177,7 +12176,7 @@ 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(); diff --git a/clang/test/Sema/c2x-expr-range.c b/clang/test/Sema/c2x-expr-range.c index 73683e6bfe684a..eff0b7cd4d9f54 100644 --- a/clang/test/Sema/c2x-expr-range.c +++ b/clang/test/Sema/c2x-expr-range.c @@ -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}} +}