Commit 82afc9b1 authored by Shawn Zhong's avatar Shawn Zhong Committed by Aaron Ballman
Browse files

Fix -Wbitfield-constant-conversion on 1-bit signed bitfield 

A one-bit signed bit-field can only hold the values 0 and -1; this
corrects the diagnostic behavior accordingly.

Fixes #53253
Differential Revision: https://reviews.llvm.org/D131255
parent e486e48c

clang/docs/ReleaseNotes.rst

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@@ -82,6 +82,9 @@ Improvements to Clang's diagnostics 
- ``-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

  `Issue 53253 <https://github.com/llvm/llvm-project/issues/53253>`_.



Non-comprehensive list of changes in this release

-------------------------------------------------

clang/lib/Sema/SemaChecking.cpp

+0 −5
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@@ -13064,11 +13064,6 @@ static bool AnalyzeBitFieldAssignment(Sema &S, FieldDecl *Bitfield, Expr *Init, 
  if (llvm::APSInt::isSameValue(Value, TruncatedValue))

    return false;













  // Special-case bitfields of width 1: booleans are naturally 0/1, and













  // therefore don't strictly fit into a signed bitfield of width 1.













  if (FieldWidth == 1 && Value == 1)













    return false;



























  std::string PrettyValue = toString(Value, 10);















  std::string PrettyTrunc = toString(TruncatedValue, 10);















































clang/test/CXX/class/class.bit/p1.cpp



+5
−5






























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@@ -9,11 +9,11 @@ struct A {













  int [[]] c : 1; // OK, attribute applies to the type.















  int : 2 = 1; // expected-error {{anonymous bit-field cannot have a default member initializer}}















  int : 0 { 1 }; // expected-error {{anonymous bit-field cannot have a default member initializer}}













  int : 0, d : 1 = 1;













  unsigned int : 0, d : 1 = 1;















  int : 1 = 12, e : 1; // expected-error {{anonymous bit-field cannot have a default member initializer}}













  int : 0, f : 1 = 1;













  int g [[]] : 1 = 1;













  int h [[]] : 1 {1};













  int i : foo() = foo();













  unsigned int : 0, f : 1 = 1;













  unsigned int g [[]] : 1 = 1;













  unsigned int h [[]] : 1 {1};













  unsigned int i : foo() = foo();















  int j, [[]] k; // expected-error {{an attribute list cannot appear here}}















};
























clang/test/CXX/drs/dr6xx.cpp



+3
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@@ -911,9 +911,9 @@ namespace dr674 { // dr674: 8













namespace dr675 { // dr675: dup 739















  template<typename T> struct A { T n : 1; };















#if __cplusplus >= 201103L













  static_assert(A<char>{1}.n < 0, "");













  static_assert(A<int>{1}.n < 0, "");













  static_assert(A<long long>{1}.n < 0, "");













  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}}















#endif















}

















































clang/test/CodeGen/bitfield.c



+16
−0






























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@@ -87,3 +87,19 @@ int g3(void) {













// PATH: ret i32 1















  return f3(20) + 130725747;















}



























static int f4(void) {













  struct s5 {













    int b:1;













  } x;













  x.b = 1;













  return x.b;













}



























int g4(void) {













// CHECK-LABEL: @g4()













// CHECK: ret i32 1













// PATH-LABEL: @g4()













// PATH: ret i32 1













  return f4() + 2;













}