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Implement a warning for known shift overflows on constant shift 

expressions. Consider the code:

  int64_t i = 10 << 30;

This compiles fine, but most developers expect it to produce the value
for 10 gigs, not -2 gigs. This is actually undefined behavior because
the LHS is a signed integer type.

The warning is currently gated behind -Wshift-overflow.

There is a special case where only the sign bit is overridden that gets
a custom error message and is by default ignored. This case is much less
likely to cause observed buggy behavior, it's just undefined behavior
according to the spec. This warning can be enabled with
-Wshift-sign-overflow.

Original patch by Oleg Slezberg, with style tweaks and some correctness
fixes by me.

llvm-svn: 126342
This commit is contained in:
Chandler Carruth 2011-02-23 23:34:11 +00:00
parent e4b316c15c
commit 4c6fdca035
8 changed files with 89 additions and 22 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
clang/include/clang/Basic/DiagnosticSemaKinds.td
View File

@ -2340,6 +2340,14 @@ def warn_division_by_zero : Warning<"division by zero is undefined">;
def warn_remainder_by_zero : Warning<"remainder by zero is undefined">;
def warn_shift_negative : Warning<"shift count is negative">;
def warn_shift_gt_typewidth : Warning<"shift count >= width of type">;
def warn_shift_result_gt_typewidth : Warning<
"shift result (%0) requires %1 bits to represent, but the promoted type of "
"the shift expression is %2 with only %3 bits">,
InGroup<DiagGroup<"shift-overflow">>;
def warn_shift_result_overrides_sign_bit : Warning<
"shift result (%0) overrides the sign bit of the promoted type of the shift "
"expression (%1) and becomes negative">,
InGroup<DiagGroup<"shift-sign-overflow">>, DefaultIgnore;
def warn_precedence_bitwise_rel : Warning<
"%0 has lower precedence than %1; %1 will be evaluated first">,

3
clang/include/clang/Sema/Sema.h
View File

@ -4790,7 +4790,8 @@ public:
QualType CheckSubtractionOperands( // C99 6.5.6
Expr *&lex, Expr *&rex, SourceLocation OpLoc, QualType* CompLHSTy = 0);
QualType CheckShiftOperands( // C99 6.5.7
Expr *&lex, Expr *&rex, SourceLocation OpLoc, bool isCompAssign = false);
Expr *&lex, Expr *&rex, SourceLocation OpLoc, unsigned Opc,
bool isCompAssign = false);
QualType CheckCompareOperands( // C99 6.5.8/9
Expr *&lex, Expr *&rex, SourceLocation OpLoc, unsigned Opc,
bool isRelational);

72
clang/lib/Sema/SemaExpr.cpp
View File

@ -6626,9 +6626,61 @@ static bool isScopedEnumerationType(QualType T) {
return false;
}
static void DiagnoseBadShiftValues(Sema& S, Expr *&lex, Expr *&rex,
SourceLocation Loc, unsigned Opc,
QualType LHSTy) {
llvm::APSInt Right;
// Check right/shifter operand
if (rex->isValueDependent() || !rex->isIntegerConstantExpr(Right, S.Context))
return;
if (Right.isNegative()) {
S.Diag(Loc, diag::warn_shift_negative) << rex->getSourceRange();
return;
}
llvm::APInt LeftBits(Right.getBitWidth(),
S.Context.getTypeSize(lex->getType()));
if (Right.uge(LeftBits)) {
S.Diag(Loc, diag::warn_shift_gt_typewidth) << rex->getSourceRange();
return;
}
if (Opc != BO_Shl)
return;
// When left shifting an ICE which is signed, we can check for overflow which
// according to C++ has undefined behavior ([expr.shift] 5.8/2). Unsigned
// integers have defined behavior modulo one more than the maximum value
// representable in the result type, so never warn for those.
llvm::APSInt Left;
if (!lex->isIntegerConstantExpr(Left, S.Context) ||
LHSTy->hasUnsignedIntegerRepresentation())
return;
llvm::APInt ResultBits =
static_cast<llvm::APInt&>(Right) + Left.getMinSignedBits();
if (LeftBits.uge(ResultBits))
return;
llvm::APSInt Result = Left.extend(ResultBits.getLimitedValue());
Result = Result.shl(Right);
// If we are only missing a sign bit, this is less likely to result in actual
// bugs -- if the result is cast back to an unsigned type, it will have the
// expected value. Thus we place this behind a different warning that can be
// turned off separately if needed.
if (LeftBits == ResultBits - 1) {
S.Diag(Loc, diag::warn_shift_result_overrides_sign_bit)
<< Result.toString(10) << LHSTy
<< lex->getSourceRange() << rex->getSourceRange();
return;
}
S.Diag(Loc, diag::warn_shift_result_gt_typewidth)
<< Result.toString(10) << Result.getMinSignedBits() << LHSTy
<< Left.getBitWidth() << lex->getSourceRange() << rex->getSourceRange();
}
// C99 6.5.7
QualType Sema::CheckShiftOperands(Expr *&lex, Expr *&rex, SourceLocation Loc,
bool isCompAssign) {
unsigned Opc, bool isCompAssign) {
// C99 6.5.7p2: Each of the operands shall have integer type.
if (!lex->getType()->hasIntegerRepresentation() ||
!rex->getType()->hasIntegerRepresentation())
@ -6659,19 +6711,7 @@ QualType Sema::CheckShiftOperands(Expr *&lex, Expr *&rex, SourceLocation Loc,
UsualUnaryConversions(rex);
// Sanity-check shift operands
llvm::APSInt Right;
// Check right/shifter operand
if (!rex->isValueDependent() &&
rex->isIntegerConstantExpr(Right, Context)) {
if (Right.isNegative())
Diag(Loc, diag::warn_shift_negative) << rex->getSourceRange();
else {
llvm::APInt LeftBits(Right.getBitWidth(),
Context.getTypeSize(lex->getType()));
if (Right.uge(LeftBits))
Diag(Loc, diag::warn_shift_gt_typewidth) << rex->getSourceRange();
}
}
DiagnoseBadShiftValues(*this, lex, rex, Loc, Opc, LHSTy);
// "The type of the result is that of the promoted left operand."
return LHSTy;
@ -7958,7 +7998,7 @@ ExprResult Sema::CreateBuiltinBinOp(SourceLocation OpLoc,
break;
case BO_Shl:
case BO_Shr:
ResultTy = CheckShiftOperands(lhs, rhs, OpLoc);
ResultTy = CheckShiftOperands(lhs, rhs, OpLoc, Opc);
break;
case BO_LE:
case BO_LT:
@ -8005,7 +8045,7 @@ ExprResult Sema::CreateBuiltinBinOp(SourceLocation OpLoc,
break;
case BO_ShlAssign:
case BO_ShrAssign:
CompResultTy = CheckShiftOperands(lhs, rhs, OpLoc, true);
CompResultTy = CheckShiftOperands(lhs, rhs, OpLoc, Opc, true);
CompLHSTy = CompResultTy;
if (!CompResultTy.isNull())
ResultTy = CheckAssignmentOperands(lhs, rhs, OpLoc, CompResultTy);

2
clang/test/Analysis/retain-release-basic-store.m
View File

@ -69,7 +69,7 @@ extern DADiskRef DADiskCopyWholeDisk( DADiskRef disk );
@interface NSAppleEventManager : NSObject {
}
@end enum {
kDAReturnSuccess = 0, kDAReturnError = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x01, kDAReturnBusy = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x02, kDAReturnBadArgument = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x03, kDAReturnExclusiveAccess = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x04, kDAReturnNoResources = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x05, kDAReturnNotFound = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x06, kDAReturnNotMounted = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x07, kDAReturnNotPermitted = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x08, kDAReturnNotPrivileged = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x09, kDAReturnNotReady = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x0A, kDAReturnNotWritable = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x0B, kDAReturnUnsupported = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x0C };
kDAReturnSuccess = 0, kDAReturnError = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x01, kDAReturnBusy = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x02, kDAReturnBadArgument = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x03, kDAReturnExclusiveAccess = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x04, kDAReturnNoResources = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x05, kDAReturnNotFound = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x06, kDAReturnNotMounted = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x07, kDAReturnNotPermitted = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x08, kDAReturnNotPrivileged = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x09, kDAReturnNotReady = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x0A, kDAReturnNotWritable = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x0B, kDAReturnUnsupported = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x0C };
typedef mach_error_t DAReturn;
typedef const struct __DADissenter * DADissenterRef;
extern DADissenterRef DADissenterCreate( CFAllocatorRef allocator, DAReturn status, CFStringRef string );

2
clang/test/Analysis/retain-release-gc-only.m
View File

@ -189,7 +189,7 @@ CVTimeStamp;
}
typedef int CIFormat;
@end enum {
kDAReturnSuccess = 0, kDAReturnError = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x01, kDAReturnBusy = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x02, kDAReturnBadArgument = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x03, kDAReturnExclusiveAccess = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x04, kDAReturnNoResources = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x05, kDAReturnNotFound = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x06, kDAReturnNotMounted = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x07, kDAReturnNotPermitted = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x08, kDAReturnNotPrivileged = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x09, kDAReturnNotReady = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x0A, kDAReturnNotWritable = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x0B, kDAReturnUnsupported = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x0C };
kDAReturnSuccess = 0, kDAReturnError = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x01, kDAReturnBusy = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x02, kDAReturnBadArgument = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x03, kDAReturnExclusiveAccess = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x04, kDAReturnNoResources = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x05, kDAReturnNotFound = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x06, kDAReturnNotMounted = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x07, kDAReturnNotPermitted = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x08, kDAReturnNotPrivileged = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x09, kDAReturnNotReady = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x0A, kDAReturnNotWritable = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x0B, kDAReturnUnsupported = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x0C };
typedef mach_error_t DAReturn;
typedef const struct __DADissenter * DADissenterRef;
extern DADissenterRef DADissenterCreate( CFAllocatorRef allocator, DAReturn status, CFStringRef string );

2
clang/test/Analysis/retain-release-region-store.m
View File

@ -75,7 +75,7 @@ extern DADiskRef DADiskCopyWholeDisk( DADiskRef disk );
@interface NSAppleEventManager : NSObject {
}
@end enum {
kDAReturnSuccess = 0, kDAReturnError = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x01, kDAReturnBusy = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x02, kDAReturnBadArgument = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x03, kDAReturnExclusiveAccess = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x04, kDAReturnNoResources = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x05, kDAReturnNotFound = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x06, kDAReturnNotMounted = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x07, kDAReturnNotPermitted = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x08, kDAReturnNotPrivileged = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x09, kDAReturnNotReady = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x0A, kDAReturnNotWritable = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x0B, kDAReturnUnsupported = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x0C };
kDAReturnSuccess = 0, kDAReturnError = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x01, kDAReturnBusy = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x02, kDAReturnBadArgument = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x03, kDAReturnExclusiveAccess = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x04, kDAReturnNoResources = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x05, kDAReturnNotFound = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x06, kDAReturnNotMounted = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x07, kDAReturnNotPermitted = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x08, kDAReturnNotPrivileged = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x09, kDAReturnNotReady = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x0A, kDAReturnNotWritable = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x0B, kDAReturnUnsupported = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x0C };
typedef mach_error_t DAReturn;
typedef const struct __DADissenter * DADissenterRef;
extern DADissenterRef DADissenterCreate( CFAllocatorRef allocator, DAReturn status, CFStringRef string );

2
clang/test/Analysis/retain-release.m
View File

@ -217,7 +217,7 @@ CVTimeStamp;
}
typedef int CIFormat;
@end enum {
kDAReturnSuccess = 0, kDAReturnError = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x01, kDAReturnBusy = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x02, kDAReturnBadArgument = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x03, kDAReturnExclusiveAccess = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x04, kDAReturnNoResources = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x05, kDAReturnNotFound = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x06, kDAReturnNotMounted = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x07, kDAReturnNotPermitted = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x08, kDAReturnNotPrivileged = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x09, kDAReturnNotReady = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x0A, kDAReturnNotWritable = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x0B, kDAReturnUnsupported = (((0x3e)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x0C };
kDAReturnSuccess = 0, kDAReturnError = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x01, kDAReturnBusy = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x02, kDAReturnBadArgument = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x03, kDAReturnExclusiveAccess = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x04, kDAReturnNoResources = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x05, kDAReturnNotFound = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x06, kDAReturnNotMounted = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x07, kDAReturnNotPermitted = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x08, kDAReturnNotPrivileged = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x09, kDAReturnNotReady = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x0A, kDAReturnNotWritable = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x0B, kDAReturnUnsupported = (((0x3eU)&0x3f)<<26) | (((0x368)&0xfff)<<14) | 0x0C };
typedef mach_error_t DAReturn;
typedef const struct __DADissenter * DADissenterRef;
extern DADissenterRef DADissenterCreate( CFAllocatorRef allocator, DAReturn status, CFStringRef string );

20
clang/test/Sema/shift.c
View File

@ -1,7 +1,9 @@
// RUN: %clang -Wall -ffreestanding -fsyntax-only -Xclang -verify %s
// RUN: %clang -Wall -Wshift-sign-overflow -ffreestanding -fsyntax-only -Xclang -verify %s
#include <limits.h>
#define WORD_BIT (sizeof(int) * CHAR_BIT)
enum {
X = 1 << 0,
Y = 1 << 1,
@ -32,6 +34,22 @@ void test() {
c <<= CHAR_BIT+1; // expected-warning {{shift count >= width of type}}
c >>= CHAR_BIT+1; // expected-warning {{shift count >= width of type}}
(void)((long)c << CHAR_BIT);
int i;
i = 1 << (WORD_BIT - 2);
i = 2 << (WORD_BIT - 1); // expected-warning {{the promoted type of the shift expression is 'int'}}
i = 1 << (WORD_BIT - 1); // expected-warning {{overrides the sign bit of the promoted type of the shift expression ('int')}}
i = -1 << (WORD_BIT - 1);
i = 0 << (WORD_BIT - 1);
i = (char)1 << (WORD_BIT - 2);
unsigned u;
u = 1U << (WORD_BIT - 1);
u = 5U << (WORD_BIT - 1);
long long int lli;
lli = INT_MIN << 2; // expected-warning {{the promoted type of the shift expression is 'int'}}
lli = 1LL << (sizeof(long long) * CHAR_BIT - 2);
}
#define a 0