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Fix a bunch of wrong "tautological unsigned enum compare" diagnostics in C++. 

An enumeration with a fixed underlying type can have any value in its
underlying type, not just those spanned by the values of its enumerators.

llvm-svn: 319875
This commit is contained in:
Richard Smith 2017-12-06 03:00:51 +00:00
parent a834b529c3
commit 371e9e8a28
2 changed files with 33 additions and 27 deletions
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7
clang/lib/Sema/SemaChecking.cpp
View File

@ -8260,11 +8260,12 @@ struct IntRange {
} else if (const EnumType *ET = dyn_cast<EnumType>(T)) {
// For enum types in C++, use the known bit width of the enumerators.
EnumDecl *Enum = ET->getDecl();
// In C++11, enums without definitions can have an explicitly specified
// underlying type. Use this type to compute the range.
if (!Enum->isCompleteDefinition())
// In C++11, enums can have a fixed underlying type. Use this type to
// compute the range.
if (Enum->isFixed()) {
return IntRange(C.getIntWidth(QualType(T, 0)),
!ET->isSignedIntegerOrEnumerationType());
}
unsigned NumPositive = Enum->getNumPositiveBits();
unsigned NumNegative = Enum->getNumNegativeBits();

53
clang/test/Sema/tautological-unsigned-enum-zero-compare.cpp
View File

@ -2,11 +2,11 @@
// RUN: %clang_cc1 -std=c++11 -triple=x86_64-pc-win32 -fsyntax-only -DSIGNED -verify %s
// RUN: %clang_cc1 -std=c++11 -triple=x86_64-pc-win32 -fsyntax-only -DSILENCE -Wno-tautological-unsigned-enum-zero-compare -verify %s
// Okay, this is where it gets complicated.
// Then default enum sigdness is target-specific.
// On windows, it is signed by default. We do not want to warn in that case.
int main() {
// On Windows, all enumerations have a fixed underlying type, which is 'int'
// if not otherwise specified, so A is identical to C on Windows. Otherwise,
// we follow the C++ rules, which say that the only valid values of A are 0
// and 1.
enum A { A_foo = 0, A_bar, };
enum A a;
@ -87,21 +87,23 @@ int main() {
if (c < 0)
return 0;
if (0 >= c) // expected-warning {{comparison 0 >= 'enum C' is always true}}
if (0 >= c)
return 0;
if (c > 0) // expected-warning {{comparison 'enum C' > 0 is always false}}
if (c > 0)
return 0;
if (0 <= c)
return 0;
if (c <= 0) // expected-warning {{comparison 'enum C' <= 0 is always true}}
if (c <= 0)
return 0;
if (0 > c)
return 0;
if (c >= 0)
return 0;
if (0 < c) // expected-warning {{0 < 'enum C' is always false}}
if (0 < c)
return 0;
// FIXME: These diagnostics are terrible. The issue here is that the signed
// enumeration value was promoted to an unsigned type.
if (c < 0U) // expected-warning {{comparison of unsigned enum expression < 0 is always false}}
return 0;
if (0U >= c)
@ -121,21 +123,23 @@ int main() {
#elif defined(SIGNED)
if (a < 0)
return 0;
if (0 >= a) // expected-warning {{comparison 0 >= 'enum A' is always true}}
if (0 >= a)
return 0;
if (a > 0) // expected-warning {{comparison 'enum A' > 0 is always false}}
if (a > 0)
return 0;
if (0 <= a)
return 0;
if (a <= 0) // expected-warning {{comparison 'enum A' <= 0 is always true}}
if (a <= 0)
return 0;
if (0 > a)
return 0;
if (a >= 0)
return 0;
if (0 < a) // expected-warning {{comparison 0 < 'enum A' is always false}}
if (0 < a)
return 0;
// FIXME: As above, the issue here is that the enumeration is promoted to
// unsigned.
if (a < 0U) // expected-warning {{comparison of unsigned enum expression < 0 is always false}}
return 0;
if (0U >= a)
@ -189,19 +193,19 @@ int main() {
if (c < 0)
return 0;
if (0 >= c) // expected-warning {{comparison 0 >= 'enum C' is always true}}
if (0 >= c)
return 0;
if (c > 0) // expected-warning {{comparison 'enum C' > 0 is always false}}
if (c > 0)
return 0;
if (0 <= c)
return 0;
if (c <= 0) // expected-warning {{comparison 'enum C' <= 0 is always true}}
if (c <= 0)
return 0;
if (0 > c)
return 0;
if (c >= 0)
return 0;
if (0 < c) // expected-warning {{0 < 'enum C' is always false}}
if (0 < c)
return 0;
if (c < 0U) // expected-warning {{comparison of unsigned enum expression < 0 is always false}}
@ -221,21 +225,22 @@ int main() {
if (0U < c)
return 0;
#else
// expected-no-diagnostics
if (a < 0)
return 0;
if (0 >= a) // expected-warning {{comparison 0 >= 'enum A' is always true}}
if (0 >= a)
return 0;
if (a > 0) // expected-warning {{comparison 'enum A' > 0 is always false}}
if (a > 0)
return 0;
if (0 <= a)
return 0;
if (a <= 0) // expected-warning {{comparison 'enum A' <= 0 is always true}}
if (a <= 0)
return 0;
if (0 > a)
return 0;
if (a >= 0)
return 0;
if (0 < a) // expected-warning {{comparison 0 < 'enum A' is always false}}
if (0 < a)
return 0;
if (a < 0U)
@ -291,19 +296,19 @@ int main() {
if (c < 0)
return 0;
if (0 >= c) // expected-warning {{comparison 0 >= 'enum C' is always true}}
if (0 >= c)
return 0;
if (c > 0) // expected-warning {{comparison 'enum C' > 0 is always false}}
if (c > 0)
return 0;
if (0 <= c)
return 0;
if (c <= 0) // expected-warning {{comparison 'enum C' <= 0 is always true}}
if (c <= 0)
return 0;
if (0 > c)
return 0;
if (c >= 0)
return 0;
if (0 < c) // expected-warning {{0 < 'enum C' is always false}}
if (0 < c)
return 0;
if (c < 0U)