[clang] 708808e - [Sema] Add check for bitfield assignments to integral types (#69049)
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Wed Oct 18 09:40:11 PDT 2023
Author: vabridgers
Date: 2023-10-18T11:40:07-05:00
New Revision: 708808e8532e7c3647356aec0664fcf94b1093d1
URL: https://github.com/llvm/llvm-project/commit/708808e8532e7c3647356aec0664fcf94b1093d1
DIFF: https://github.com/llvm/llvm-project/commit/708808e8532e7c3647356aec0664fcf94b1093d1.diff
LOG: [Sema] Add check for bitfield assignments to integral types (#69049)
This change introduces the bitfield conversion check after fixes to the
test case. The original submission unfortunately did not comprehend
differences in architecture for the diagnostic messages, leading to
unanticipated failures in the arm build bots.
Original PR: https://github.com/llvm/llvm-project/pull/68276
Clang does not check for bitfield assignment widths, while gcc checks
this.
gcc produced a warning like so for it's -Wconversion flag:
```
$ gcc -Wconversion -c test.c
test.c: In function 'foo':
test.c:10:15: warning: conversion from 'int' to 'signed char:7' may
change value [-Wconversion]
10 | vxx.bf = x; // no warning
| ^
```
This change simply adds this check for integral types under the
-Wbitfield-conversion compiler option.
Added:
clang/test/SemaCXX/bitfield-width.c
Modified:
clang/docs/ReleaseNotes.rst
clang/include/clang/Basic/DiagnosticGroups.td
clang/include/clang/Basic/DiagnosticSemaKinds.td
clang/lib/Sema/SemaChecking.cpp
Removed:
################################################################################
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 17d9b9f81cd5fdd..1e77386aede2e5d 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -197,6 +197,9 @@ New Compiler Flags
the preprocessed text to the output. This can greatly reduce the size of the
preprocessed output, which can be helpful when trying to reduce a test case.
+* ``-Wbitfield-conversion`` was added to detect assignments of integral
+ types to a bitfield that may change the value.
+
Deprecated Compiler Flags
-------------------------
diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
index 0b09c002191848a..674eb9f4ef2e73f 100644
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -53,6 +53,7 @@ def SingleBitBitFieldConstantConversion :
def BitFieldConstantConversion : DiagGroup<"bitfield-constant-conversion",
[SingleBitBitFieldConstantConversion]>;
def BitFieldEnumConversion : DiagGroup<"bitfield-enum-conversion">;
+def BitFieldConversion : DiagGroup<"bitfield-conversion">;
def BitFieldWidth : DiagGroup<"bitfield-width">;
def CompoundTokenSplitByMacro : DiagGroup<"compound-token-split-by-macro">;
def CompoundTokenSplitBySpace : DiagGroup<"compound-token-split-by-space">;
@@ -933,6 +934,7 @@ def Conversion : DiagGroup<"conversion",
ConstantConversion,
EnumConversion,
BitFieldEnumConversion,
+ BitFieldConversion,
FloatConversion,
Shorten64To32,
IntConversion,
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 58a33e2807b7b0a..7f39f5e79792c07 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -6171,6 +6171,9 @@ def warn_signed_bitfield_enum_conversion : Warning<
"signed bit-field %0 needs an extra bit to represent the largest positive "
"enumerators of %1">,
InGroup<BitFieldEnumConversion>, DefaultIgnore;
+def warn_bitfield_too_small_for_integral_type : Warning<
+ "conversion from %2 (%3 bits) to bit-field %0 (%1 bits) may change value">,
+ InGroup<BitFieldConversion>, DefaultIgnore;
def note_change_bitfield_sign : Note<
"consider making the bitfield type %select{unsigned|signed}0">;
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 31b7e6cc8b8922a..cd7c26a84b6cce0 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -14331,6 +14331,18 @@ static bool AnalyzeBitFieldAssignment(Sema &S, FieldDecl *Bitfield, Expr *Init,
S.Diag(WidthExpr->getExprLoc(), diag::note_widen_bitfield)
<< BitsNeeded << ED << WidthExpr->getSourceRange();
}
+ } else if (OriginalInit->getType()->isIntegralType(S.Context)) {
+ IntRange LikelySourceRange =
+ GetExprRange(S.Context, Init, S.isConstantEvaluatedContext(),
+ /*Approximate=*/true);
+
+ if (LikelySourceRange.Width > FieldWidth) {
+ Expr *WidthExpr = Bitfield->getBitWidth();
+ S.Diag(InitLoc, diag::warn_bitfield_too_small_for_integral_type)
+ << Bitfield << FieldWidth << OriginalInit->getType()
+ << LikelySourceRange.Width;
+ S.Diag(WidthExpr->getExprLoc(), diag::note_declared_at);
+ }
}
return false;
@@ -15228,7 +15240,6 @@ static void CheckImplicitConversion(Sema &S, Expr *E, QualType T,
if (LikelySourceRange.Width > TargetRange.Width) {
// If the source is a constant, use a default-on diagnostic.
- // TODO: this should happen for bitfield stores, too.
Expr::EvalResult Result;
if (E->EvaluateAsInt(Result, S.Context, Expr::SE_AllowSideEffects,
S.isConstantEvaluatedContext())) {
diff --git a/clang/test/SemaCXX/bitfield-width.c b/clang/test/SemaCXX/bitfield-width.c
new file mode 100644
index 000000000000000..7b4e4444c245b0e
--- /dev/null
+++ b/clang/test/SemaCXX/bitfield-width.c
@@ -0,0 +1,42 @@
+// RUN: %clang_cc1 -Wconversion -fsyntax-only -verify %s
+// RUN: %clang_cc1 -Wbitfield-conversion -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple armebv7-unknown-linux -Wbitfield-conversion \
+// RUN: -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple arm64-unknown-linux -Wbitfield-conversion \
+// RUN: -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple arm-unknown-linux -Wbitfield-conversion \
+// RUN: -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple aarch64-unknown-linux -Wbitfield-conversion \
+// RUN: -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple mipsel-unknown-linux -Wbitfield-conversion \
+// RUN: -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple mips64el-unknown-linux -Wbitfield-conversion \
+// RUN: -fsyntax-only -verify %s
+
+typedef struct _xx {
+ int bf:9; // expected-note 3{{declared here}}
+ } xx, *pxx;
+
+ xx vxx;
+
+ void foo1(int x) {
+ vxx.bf = x; // expected-warning{{conversion from 'int' (32 bits) to bit-field 'bf' (9 bits) may change value}}
+ }
+ void foo2(short x) {
+ vxx.bf = x; // expected-warning{{conversion from 'short' (16 bits) to bit-field 'bf' (9 bits) may change value}}
+ }
+ void foo3(char x) {
+ vxx.bf = x; // no warning expected
+ }
+ void foo4(short x) {
+ vxx.bf = 0xff & x; // no warning expected
+ }
+ void foo5(short x) {
+ vxx.bf = 0x1ff & x; // no warning expected
+ }
+ void foo6(short x) {
+ vxx.bf = 0x3ff & x; // expected-warning{{conversion from 'int' (10 bits) to bit-field 'bf' (9 bits) may change value}}
+ }
+ int fee(void) {
+ return 0;
+ }
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