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Make the bitfield implicit truncation warning slightly more aggressive, and make the printed warning a bit more accurate. The new behavior matches gcc's -Wconversion. <rdar://problem/10238797>. 

llvm-svn: 149089
This commit is contained in:
Eli Friedman 2012-01-26 23:11:39 +00:00
parent fc9dce25f7
commit c267a32b05
2 changed files with 21 additions and 10 deletions
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17
clang/lib/Sema/SemaChecking.cpp
View File

@ -3655,19 +3655,20 @@ bool AnalyzeBitFieldAssignment(Sema &S, FieldDecl *Bitfield, Expr *Init,
if (OriginalWidth <= FieldWidth)
return false;
// Compute the value which the bitfield will contain.
llvm::APSInt TruncatedValue = Value.trunc(FieldWidth);
TruncatedValue.setIsSigned(Bitfield->getType()->isSignedIntegerType());
// It's fairly common to write values into signed bitfields
// that, if sign-extended, would end up becoming a different
// value. We don't want to warn about that.
if (Value.isSigned() && Value.isNegative())
TruncatedValue = TruncatedValue.sext(OriginalWidth);
else
TruncatedValue = TruncatedValue.zext(OriginalWidth);
// Check whether the stored value is equal to the original value.
TruncatedValue = TruncatedValue.extend(OriginalWidth);
if (Value == TruncatedValue)
return false;
// Special-case bitfields of width 1: booleans are naturally 0/1, and
// therefore don't strictly fit into a bitfield of width 1.
if (FieldWidth == 1 && Value.getBoolValue() == TruncatedValue.getBoolValue())
return false;
std::string PrettyValue = Value.toString(10);
std::string PrettyTrunc = TruncatedValue.toString(10);

14
clang/test/Sema/constant-conversion.c
View File

@ -31,8 +31,8 @@ void test3() {
int bar : 2;
};
struct A a = { 0, 10 }; // expected-warning {{implicit truncation from 'int' to bitfield changes value from 10 to 2}}
struct A b[] = { 0, 10, 0, 0 }; // expected-warning {{implicit truncation from 'int' to bitfield changes value from 10 to 2}}
struct A a = { 0, 10 }; // expected-warning {{implicit truncation from 'int' to bitfield changes value from 10 to -2}}
struct A b[] = { 0, 10, 0, 0 }; // expected-warning {{implicit truncation from 'int' to bitfield changes value from 10 to -2}}
struct A c[] = {{10, 0}}; // expected-warning {{implicit truncation from 'int' to bitfield changes value from 10 to 2}}
struct A d = (struct A) { 10, 0 }; // expected-warning {{implicit truncation from 'int' to bitfield changes value from 10 to 2}}
struct A e = { .foo = 10 }; // expected-warning {{implicit truncation from 'int' to bitfield changes value from 10 to 2}}
@ -62,3 +62,13 @@ void test6() {
unsigned char y = 1 ? 65535 : 1; // expected-warning {{changes value}}
}
void test7() {
struct {
unsigned int twoBits1:2;
unsigned int twoBits2:2;
unsigned int reserved:28;
} f;
f.twoBits1 = ~1; // expected-warning {{implicit truncation from 'int' to bitfield changes value from -2 to 2}}
f.twoBits2 = ~2; // expected-warning {{implicit truncation from 'int' to bitfield changes value from -3 to 1}}
}