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Added warning for unary minus used with unsigned type 

Summary:
Inspired by MSVC, which found some occurrences of this expression on our code base.

Fixes PR38950

Reviewers: rsmith, craig.topper, spatel, RKSimon, aaron.ballman, thakis

Reviewed By: rsmith

Subscribers: joerg, Quuxplusone, lebedev.ri, craig.topper, RKSimon, cfe-commits

Differential Revision: https://reviews.llvm.org/D52137

llvm-svn: 343560
This commit is contained in:
David Bolvansky 2018-10-02 06:02:30 +00:00
parent ab41193312
commit cf7d2256d6
3 changed files with 39 additions and 0 deletions
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6
clang/include/clang/Basic/DiagnosticSemaKinds.td
View File

@ -3197,6 +3197,12 @@ def warn_impcast_integer_sign_conditional : Warning<
def warn_impcast_integer_precision : Warning<
"implicit conversion loses integer precision: %0 to %1">,
InGroup<Conversion>, DefaultIgnore;
def warn_impcast_high_order_zero_bits : Warning<
"higher order bits are zeroes after implicit conversion">,
InGroup<Conversion>, DefaultIgnore;
def warn_impcast_nonnegative_result : Warning<
"the resulting value is always non-negative after implicit conversion">,
InGroup<SignConversion>, DefaultIgnore;
def warn_impcast_integer_64_32 : Warning<
"implicit conversion loses integer precision: %0 to %1">,
InGroup<Shorten64To32>, DefaultIgnore;

13
clang/lib/Sema/SemaChecking.cpp
View File

@ -10896,6 +10896,19 @@ CheckImplicitConversion(Sema &S, Expr *E, QualType T, SourceLocation CC,
return DiagnoseImpCast(S, E, T, CC, diag::warn_impcast_integer_precision);
}
if (TargetRange.Width > SourceRange.Width) {
if (auto *UO = dyn_cast<UnaryOperator>(E))
if (UO->getOpcode() == UO_Minus)
if (Source->isUnsignedIntegerType()) {
if (Target->isUnsignedIntegerType())
return DiagnoseImpCast(S, E, T, CC,
diag::warn_impcast_high_order_zero_bits);
if (Target->isSignedIntegerType())
return DiagnoseImpCast(S, E, T, CC,
diag::warn_impcast_nonnegative_result);
}
}
if (TargetRange.Width == SourceRange.Width && !TargetRange.NonNegative &&
SourceRange.NonNegative && Source->isSignedIntegerType()) {
// Warn when doing a signed to signed conversion, warn if the positive

20
clang/test/Sema/unary-minus-integer-impcast.c Normal file
View File

@ -0,0 +1,20 @@
// RUN: %clang_cc1 %s -verify -Wconversion -fsyntax-only -triple x86_64-pc-linux-gnu
// RUN: %clang_cc1 %s -verify -Wconversion -fsyntax-only -triple i386-pc-linux-gnu
void test(void) {
unsigned int a = 1;
unsigned long long b = -a; // expected-warning {{higher order bits are zeroes after implicit conversion}}
long long c = -a; // expected-warning {{the resulting value is always non-negative after implicit conversion}}
unsigned long b2 = -a;
#ifdef __x86_64__
// expected-warning@-2 {{higher order bits are zeroes after implicit conversion}}
#endif
long c2 = -a;
#ifdef __x86_64__
// expected-warning@-2 {{the resulting value is always non-negative after implicit conversion}}
#else
// expected-warning@-4 {{implicit conversion changes signedness: 'unsigned int' to 'long'}}
#endif
}