AntonBikineev created this revision.
AntonBikineev added reviewers: aaron.ballman, thakis.
AntonBikineev requested review of this revision.
Herald added a project: clang.
This change splits '-Wtautological-unsigned-zero-compare' by reporting
char-expressions-interpreted-as-unsigned under a separate diagnostic
'-Wtautological-unsigned-char-zero-compare'. This is beneficial for
projects that want to enable '-Wtautological-unsigned-zero-compare' but at
the same time want to keep code portable for platforms with char being
signed or unsigned, such as Chromium.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D99808
Files:
clang/include/clang/Basic/DiagnosticGroups.td
clang/include/clang/Basic/DiagnosticSemaKinds.td
clang/lib/Sema/SemaChecking.cpp
clang/test/Sema/tautological-unsigned-char-zero-compare.cc
Index: clang/test/Sema/tautological-unsigned-char-zero-compare.cc
===================================================================
--- /dev/null
+++ clang/test/Sema/tautological-unsigned-char-zero-compare.cc
@@ -0,0 +1,39 @@
+// RUN: %clang_cc1 -fsyntax-only \
+// RUN: -fno-signed-char \
+// RUN: -Wtautological-unsigned-zero-compare \
+// RUN: -Wtautological-unsigned-char-zero-compare \
+// RUN: -verify=unsigned %s
+// RUN: %clang_cc1 -fsyntax-only \
+// RUN: -Wtautological-unsigned-zero-compare \
+// RUN: -Wtautological-unsigned-char-zero-compare \
+// RUN: -verify=signed %s
+
+void f(char c, unsigned char uc, signed char cc) {
+ if (c < 0)
+ return;
+ // unsigned-warning@-2 {{comparison of char expression < 0 is always false, since char is interpreted as unsigned}}
+ if (uc < 0)
+ return;
+ // unsigned-warning@-2 {{comparison of unsigned expression < 0 is always false}}
+ // signed-warning@-3 {{comparison of unsigned expression < 0 is always false}}
+ if (cc < 0)
+ return;
+ // Promoted to integer expressions should not warn.
+ if (c - 4 < 0)
+ return;
+}
+
+void ref(char &c, unsigned char &uc, signed char &cc) {
+ if (c < 0)
+ return;
+ // unsigned-warning@-2 {{comparison of char expression < 0 is always false, since char is interpreted as unsigned}}
+ if (uc < 0)
+ return;
+ // unsigned-warning@-2 {{comparison of unsigned expression < 0 is always false}}
+ // signed-warning@-3 {{comparison of unsigned expression < 0 is always false}}
+ if (cc < 0)
+ return;
+ // Promoted to integer expressions should not warn.
+ if (c - 4 < 0)
+ return;
+}
Index: clang/lib/Sema/SemaChecking.cpp
===================================================================
--- clang/lib/Sema/SemaChecking.cpp
+++ clang/lib/Sema/SemaChecking.cpp
@@ -11415,11 +11415,14 @@
<< OtherIsBooleanDespiteType << *Result
<< E->getLHS()->getSourceRange() << E->getRHS()->getSourceRange());
} else {
- unsigned Diag = (isKnownToHaveUnsignedValue(OriginalOther) && Value == 0)
- ? (HasEnumType(OriginalOther)
- ? diag::warn_unsigned_enum_always_true_comparison
- : diag::warn_unsigned_always_true_comparison)
- : diag::warn_tautological_constant_compare;
+ bool IsCharTy = OtherT.withoutLocalFastQualifiers() == S.Context.CharTy;
+ unsigned Diag =
+ (isKnownToHaveUnsignedValue(OriginalOther) && Value == 0)
+ ? (HasEnumType(OriginalOther)
+ ? diag::warn_unsigned_enum_always_true_comparison
+ : IsCharTy ? diag::warn_unsigned_char_always_true_comparison
+ : diag::warn_unsigned_always_true_comparison)
+ : diag::warn_tautological_constant_compare;
S.Diag(E->getOperatorLoc(), Diag)
<< RhsConstant << OtherT << E->getOpcodeStr() << OS.str() << *Result
Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -6784,6 +6784,10 @@
"result of comparison of %select{%3|unsigned expression}0 %2 "
"%select{unsigned expression|%3}0 is always %4">,
InGroup<TautologicalUnsignedZeroCompare>, DefaultIgnore;
+def warn_unsigned_char_always_true_comparison : Warning<
+ "result of comparison of %select{%3|char expression}0 %2 "
+ "%select{char expression|%3}0 is always %4, since char is interpreted as "
+ "unsigned">, InGroup<TautologicalUnsignedCharZeroCompare>, DefaultIgnore;
def warn_unsigned_enum_always_true_comparison : Warning<
"result of comparison of %select{%3|unsigned enum expression}0 %2 "
"%select{unsigned enum expression|%3}0 is always %4">,
Index: clang/include/clang/Basic/DiagnosticGroups.td
===================================================================
--- clang/include/clang/Basic/DiagnosticGroups.td
+++ clang/include/clang/Basic/DiagnosticGroups.td
@@ -591,11 +591,13 @@
def IntInBoolContext : DiagGroup<"int-in-bool-context">;
def TautologicalTypeLimitCompare : DiagGroup<"tautological-type-limit-compare">;
def TautologicalUnsignedZeroCompare : DiagGroup<"tautological-unsigned-zero-compare">;
+def TautologicalUnsignedCharZeroCompare : DiagGroup<"tautological-unsigned-char-zero-compare">;
def TautologicalUnsignedEnumZeroCompare : DiagGroup<"tautological-unsigned-enum-zero-compare">;
// For compatibility with GCC. Tautological comparison warnings for constants
// that are an extremal value of the type.
def TypeLimits : DiagGroup<"type-limits", [TautologicalTypeLimitCompare,
TautologicalUnsignedZeroCompare,
+ TautologicalUnsignedCharZeroCompare,
TautologicalUnsignedEnumZeroCompare]>;
// Additional tautological comparison warnings based on the expression, not
// only on its type.
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