aaron.ballman created this revision.
aaron.ballman added reviewers: ShawnZhong, thakis, clang-language-wg,
erichkeane.
Herald added a project: All.
aaron.ballman requested review of this revision.
Herald added a project: clang.
https://reviews.llvm.org/D131255 (82afc9b169a67e8b8a1862fb9c41a2cd974d6691
<https://reviews.llvm.org/rG82afc9b169a67e8b8a1862fb9c41a2cd974d6691>) began
warning about conversion causing data loss for a single-bit bit-field. However,
after landing the changes, there were reports about significant false positives
from some code bases.
This alters the approach taken in that patch by introducing a new warning group
(`-Wsingle-bit-bitfield-constant-conversion`) which is grouped under
`-Wbitfield-constant-conversion` to allow users to selectively disable the
single-bit warning without losing the other constant conversion warnings.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D132851
Files:
clang/docs/ReleaseNotes.rst
clang/include/clang/Basic/DiagnosticGroups.td
clang/include/clang/Basic/DiagnosticSemaKinds.td
clang/lib/Sema/SemaChecking.cpp
clang/test/CXX/drs/dr6xx.cpp
clang/test/Sema/constant-conversion.c
Index: clang/test/Sema/constant-conversion.c
===================================================================
--- clang/test/Sema/constant-conversion.c
+++ clang/test/Sema/constant-conversion.c
@@ -1,4 +1,5 @@
-// RUN: %clang_cc1 -fsyntax-only -verify -triple x86_64-apple-darwin %s
+// RUN: %clang_cc1 -fsyntax-only -verify=expected,one-bit -triple x86_64-apple-darwin %s
+// RUN: %clang_cc1 -fsyntax-only -Wno-single-bit-bitfield-constant-conversion -verify -triple x86_64-apple-darwin %s
// This file tests -Wconstant-conversion, a subcategory of -Wconversion
// which is on by default.
@@ -23,7 +24,7 @@
s.b = -2; // expected-warning {{implicit truncation from 'int' to bit-field changes value from -2 to 0}}
s.b = -1; // no-warning
s.b = 0; // no-warning
- s.b = 1; // expected-warning {{implicit truncation from 'int' to bit-field changes value from 1 to -1}}
+ s.b = 1; // one-bit-warning {{implicit truncation from 'int' to a one-bit wide bit-field changes value from 1 to -1}}
s.b = 2; // expected-warning {{implicit truncation from 'int' to bit-field changes value from 2 to 0}}
}
Index: clang/test/CXX/drs/dr6xx.cpp
===================================================================
--- clang/test/CXX/drs/dr6xx.cpp
+++ clang/test/CXX/drs/dr6xx.cpp
@@ -911,9 +911,9 @@
namespace dr675 { // dr675: dup 739
template<typename T> struct A { T n : 1; };
#if __cplusplus >= 201103L
- static_assert(A<char>{1}.n < 0, ""); // expected-warning {{implicit truncation from 'int' to bit-field changes value from 1 to -1}}
- static_assert(A<int>{1}.n < 0, ""); // expected-warning {{implicit truncation from 'int' to bit-field changes value from 1 to -1}}
- static_assert(A<long long>{1}.n < 0, ""); // expected-warning {{implicit truncation from 'int' to bit-field changes value from 1 to -1}}
+ static_assert(A<char>{1}.n < 0, ""); // expected-warning {{implicit truncation from 'int' to a one-bit wide bit-field changes value from 1 to -1}}
+ static_assert(A<int>{1}.n < 0, ""); // expected-warning {{implicit truncation from 'int' to a one-bit wide bit-field changes value from 1 to -1}}
+ static_assert(A<long long>{1}.n < 0, ""); // expected-warning {{implicit truncation from 'int' to a one-bit wide bit-field changes value from 1 to -1}}
#endif
}
Index: clang/lib/Sema/SemaChecking.cpp
===================================================================
--- clang/lib/Sema/SemaChecking.cpp
+++ clang/lib/Sema/SemaChecking.cpp
@@ -13067,9 +13067,12 @@
std::string PrettyValue = toString(Value, 10);
std::string PrettyTrunc = toString(TruncatedValue, 10);
- S.Diag(InitLoc, diag::warn_impcast_bitfield_precision_constant)
- << PrettyValue << PrettyTrunc << OriginalInit->getType()
- << Init->getSourceRange();
+ bool IsOneBit = FieldWidth == 1 && Value == 1;
+ S.Diag(InitLoc, IsOneBit
+ ? diag::warn_impcast_single_bit_bitield_precision_constant
+ : diag::warn_impcast_bitfield_precision_constant)
+ << PrettyValue << PrettyTrunc << OriginalInit->getType()
+ << Init->getSourceRange();
return true;
}
Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -3846,6 +3846,9 @@
def warn_impcast_integer_precision_constant : Warning<
"implicit conversion from %2 to %3 changes value from %0 to %1">,
InGroup<ConstantConversion>;
+def warn_impcast_single_bit_bitield_precision_constant : Warning<
+ "implicit truncation from %2 to a one-bit wide bit-field changes value from "
+ "%0 to %1">, InGroup<SingleBitBitFieldConstantConversion>;
def warn_impcast_bitfield_precision_constant : Warning<
"implicit truncation from %2 to bit-field changes value from %0 to %1">,
InGroup<BitFieldConstantConversion>;
Index: clang/include/clang/Basic/DiagnosticGroups.td
===================================================================
--- clang/include/clang/Basic/DiagnosticGroups.td
+++ clang/include/clang/Basic/DiagnosticGroups.td
@@ -47,7 +47,10 @@
CXXPre14CompatBinaryLiteral,
GNUBinaryLiteral]>;
def GNUCompoundLiteralInitializer : DiagGroup<"gnu-compound-literal-initializer">;
-def BitFieldConstantConversion : DiagGroup<"bitfield-constant-conversion">;
+def SingleBitBitFieldConstantConversion :
+ DiagGroup<"single-bit-bitfield-constant-conversion">;
+def BitFieldConstantConversion : DiagGroup<"bitfield-constant-conversion",
+ [SingleBitBitFieldConstantConversion]>;
def BitFieldEnumConversion : DiagGroup<"bitfield-enum-conversion">;
def BitFieldWidth : DiagGroup<"bitfield-width">;
def CompoundTokenSplitByMacro : DiagGroup<"compound-token-split-by-macro">;
Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -101,8 +101,9 @@
- ``-Wformat`` now recognizes ``%b`` for the ``printf``/``scanf`` family of
functions and ``%B`` for the ``printf`` family of functions. Fixes
`Issue 56885: <https://github.com/llvm/llvm-project/issues/56885>`_.
-- ``-Wbitfield-constant-conversion`` now diagnoses implicit truncation when 1 is
- assigned to a 1-bit signed integer bitfield. This fixes
+- Introduced ``-Wsingle-bit-bitfield-constant-conversion``, grouped under
+ ``-Wbitfield-constant-conversion``, which diagnoses implicit truncation when
+ ``1`` is assigned to a 1-bit signed integer bitfield. This fixes
`Issue 53253 <https://github.com/llvm/llvm-project/issues/53253>`_.
- ``-Wincompatible-function-pointer-types`` now defaults to an error in all C
language modes. It may be downgraded to a warning with
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