Perhaps like this?
On Fri, Nov 14, 2014 at 01:17:38PM -0800, David Blaikie wrote:
> Yep. Though the diagnostic for dropping const and volatile is a bit off
> ("drops const volatile qualifier" should probably read "drops const and
> volatile qualifiers"? (maybe you'll need a %select for this - you could
> probably use a %select for the const and volatile separately too if you
> like)). What does GCC do here? Does it warn on dropping volatile at all?
>
> Chatting to Richard over lunch he mentioned an interesting case where we
> might want to warn:
>
> int **x;
> auto y = (const int **)x;
>
> which, if it were a static_cast, would warn:
>
> cast.cpp:2:10: error: static_cast from 'int **' to 'const int **' is not
> allowed
> auto y = static_cast<const int **>(x);
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> I'm just not sure we'll be able to get a good diagnostic in both these
> cases. But as I think/type this out I think:
>
> We should just use the same machinery that powers static_cast here,
> (Richard mentioned there should be a way to test whether a conversion is a
> "qualification conversion" which is the description of the valid implicit
> qualification changes, and not the above const-changing cases)) and we
> should teach the machinery to give us enough information to create good
> diagnostics - telling the user where the missing const, volatile, etc, is.
>
> Sorry to go through so many iterations - it didn't occur to me until
> Richard mentioned it that there was this more general approach.
>
> (wonder what GCC does here? - hmm, looks like it gets the "int** -> const
> int**" right: cast from type ???int**??? to type ???const int**??? casts away
> qualifiers)
>
> On Fri, Nov 14, 2014 at 12:02 PM, Roman Divacky <[email protected]> wrote:
>
> > Like this?
> >
> > On Fri, Nov 14, 2014 at 11:20:49AM -0800, David Blaikie wrote:
> > > I take it this is consistent with the GCC warning - in terms of warning
> > on
> > > the innermost issue, reporting const or volatile - what about dropping
> > > const and volatile at the same time?
> > >
> > > Issues with the current code:
> > >
> > > * DestPtr and SrcPtr don't need to be initialized to null, they'll be
> > > written to on the first loop iteration as needed - avoiding excess
> > > initialization helps tools like MSan find more bugs rather than the
> > program
> > > silently using unintended default values
> > >
> > > * InnerMostDestType and InnerMostSrcType will be dangling pointers after
> > > the while loop (so accessing them in the proceeding 'if' is UB)
> > >
> > > * you don't need to check both InnerMostDestType and InnerMostSrcType in
> > > the following if - it's invariant that if one is non-null (you can use
> > > QualType values rather than QualType* to address the previous bug, and
> > use
> > > QualTypes "isNull()" member function here) so is the other
> > >
> > > On Fri, Nov 14, 2014 at 11:07 AM, Roman Divacky <[email protected]>
> > wrote:
> > >
> > > > Actually, try this patch. It includes check for volatile as well.
> > > >
> > > > On Wed, Nov 12, 2014 at 12:39:20PM -0800, David Blaikie wrote:
> > > > > [+Richard for oversight]
> > > > >
> > > > > char **y1 = (char **)ptrptr; // expected-warning {{cast from 'const
> > char
> > > > > *const *' to 'char **' drops const qualifier}} expected-warning
> > {{cast
> > > > from
> > > > > 'const char *const' to 'char *' drops const qualifier}}
> > > > >
> > > > > I think if we're going to warn on multiple layers (I'm not sure
> > that's
> > > > > ideal - is that consistent with GCC's warning? Does GCC warn on
> > > > mismatched
> > > > > types too - "const T*" -> "U*"? - do we warn there too, or only when
> > > > > there's a valid implicit conversion like the void* example?) then we
> > > > should
> > > > > probably drop the top level const, "const char *const" -> "char*" -
> > the
> > > > top
> > > > > level const on the first type is confusing/misleading, it's only
> > relevant
> > > > > to show "const char*" and "char*".
> > > > >
> > > > >
> > > > > On Wed, Nov 12, 2014 at 10:41 AM, Roman Divacky <[email protected]>
> > > > wrote:
> > > > >
> > > > > > I expanded the testcase and fixed the grammar in the actual
> > warning.
> > > > > >
> > > > > > New patch attached.
> > > > > >
> > > > > > On Tue, Nov 11, 2014 at 05:03:33PM -0800, David Blaikie wrote:
> > > > > > > (it's a bit easier if you include the test in the same patch
> > file -
> > > > also
> > > > > > > you can use Phabricator if you like - some reviewers perefer it)
> > > > > > >
> > > > > > > Since you've got the loop there for seeing through multiple
> > levels of
> > > > > > > pointer, should you have a test case that exercises that on a > 1
> > > > level
> > > > > > of
> > > > > > > depth? Demonstrate that we warn on both levels (if that's the
> > right
> > > > thing
> > > > > > > to do?)?
> > > > > > >
> > > > > > > Optionally (probably in a separate follow-up patch) you could
> > add a
> > > > note
> > > > > > > with a fixit to include the missing consts.
> > > > > > >
> > > > > > > On Tue, Nov 11, 2014 at 10:58 AM, Roman Divacky <
> > [email protected]>
> > > > > > wrote:
> > > > > > >
> > > > > > > > Hi,
> > > > > > > >
> > > > > > > > I implemented -Wcast-qual. The patch is actually quite short
> > > > (attached
> > > > > > + a
> > > > > > > > test
> > > > > > > > case).
> > > > > > > >
> > > > > > > > This fixes #13772 and also note that -Wcast-qual is used in
> > llvm
> > > > build
> > > > > > > > itself.
> > > > > > > >
> > > > > > > > Is this ok to be commited? Thanks
> > > > > > > >
> > > > > > > > Roman
> > > > > > > >
> > > > > > > >
> > > > > > > > _______________________________________________
> > > > > > > > cfe-commits mailing list
> > > > > > > > [email protected]
> > > > > > > > http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
> > > > > > > >
> > > > > > > >
> > > > > >
> > > >
> >
Index: include/clang/Basic/DiagnosticGroups.td
===================================================================
--- include/clang/Basic/DiagnosticGroups.td (revision 222228)
+++ include/clang/Basic/DiagnosticGroups.td (working copy)
@@ -60,7 +60,7 @@
def KeywordCompat : DiagGroup<"keyword-compat">;
def GNUCaseRange : DiagGroup<"gnu-case-range">;
def CastAlign : DiagGroup<"cast-align">;
-def : DiagGroup<"cast-qual">;
+def CastQual : DiagGroup<"cast-qual">;
def : DiagGroup<"char-align">;
def Comment : DiagGroup<"comment">;
def GNUComplexInteger : DiagGroup<"gnu-complex-integer">;
Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td (revision 222228)
+++ include/clang/Basic/DiagnosticSemaKinds.td (working copy)
@@ -6104,6 +6104,8 @@
def warn_zero_size_struct_union_in_extern_c : Warning<"%select{|empty }0"
"%select{struct|union}1 has size 0 in C, %select{size 1|non-zero size}2 in C++">,
InGroup<ExternCCompat>;
+def warn_cast_qual : Warning<"cast from %0 to %1 drops %2 qualifier%3">,
+ InGroup<CastQual>, DefaultIgnore;
} // End of general sema category.
// inline asm.
Index: lib/Sema/SemaCast.cpp
===================================================================
--- lib/Sema/SemaCast.cpp (revision 222228)
+++ lib/Sema/SemaCast.cpp (working copy)
@@ -143,7 +143,10 @@
}
static bool CastsAwayConstness(Sema &Self, QualType SrcType, QualType DestType,
- bool CheckCVR, bool CheckObjCLifetime);
+ bool CheckCVR, bool CheckObjCLifetime,
+ QualType *TheOffendingSrcType = nullptr,
+ QualType *TheOffendingDestType = nullptr,
+ Qualifiers *CastAwayQualifiers = nullptr);
// The Try functions attempt a specific way of casting. If they succeed, they
// return TC_Success. If their way of casting is not appropriate for the given
@@ -462,7 +465,10 @@
/// \param CheckObjCLifetime Whether to check Objective-C lifetime qualifiers.
static bool
CastsAwayConstness(Sema &Self, QualType SrcType, QualType DestType,
- bool CheckCVR, bool CheckObjCLifetime) {
+ bool CheckCVR, bool CheckObjCLifetime,
+ QualType *TheOffendingSrcType,
+ QualType *TheOffendingDestType,
+ Qualifiers *CastAwayQualifiers) {
// If the only checking we care about is for Objective-C lifetime qualifiers,
// and we're not in ARC mode, there's nothing to check.
if (!CheckCVR && CheckObjCLifetime &&
@@ -487,6 +493,8 @@
// Find the qualifiers. We only care about cvr-qualifiers for the
// purpose of this check, because other qualifiers (address spaces,
// Objective-C GC, etc.) are part of the type's identity.
+ QualType PrevUnwrappedSrcType = UnwrappedSrcType;
+ QualType PrevUnwrappedDestType = UnwrappedDestType;
while (UnwrapDissimilarPointerTypes(UnwrappedSrcType, UnwrappedDestType)) {
// Determine the relevant qualifiers at this level.
Qualifiers SrcQuals, DestQuals;
@@ -497,6 +505,13 @@
if (CheckCVR) {
RetainedSrcQuals.setCVRQualifiers(SrcQuals.getCVRQualifiers());
RetainedDestQuals.setCVRQualifiers(DestQuals.getCVRQualifiers());
+
+ if (RetainedSrcQuals != RetainedDestQuals && TheOffendingSrcType &&
+ TheOffendingDestType && CastAwayQualifiers) {
+ *TheOffendingSrcType = PrevUnwrappedSrcType;
+ *TheOffendingDestType = PrevUnwrappedDestType;
+ *CastAwayQualifiers = RetainedSrcQuals - RetainedDestQuals;
+ }
}
if (CheckObjCLifetime &&
@@ -505,6 +520,9 @@
cv1.push_back(RetainedSrcQuals);
cv2.push_back(RetainedDestQuals);
+
+ PrevUnwrappedSrcType = UnwrappedSrcType;
+ PrevUnwrappedDestType = UnwrappedDestType;
}
if (cv1.empty())
return false;
@@ -2371,6 +2389,28 @@
if (Kind == CK_BitCast)
checkCastAlign();
+
+ // -Wcast-qual
+ QualType TheOffendingSrcType, TheOffendingDestType;
+ Qualifiers CastAwayQualifiers;
+ if (CastsAwayConstness(Self, SrcType, DestType, true, false,
+ &TheOffendingSrcType, &TheOffendingDestType,
+ &CastAwayQualifiers)) {
+ const char *qualifiers;
+ const char *suffix = "";
+ if (CastAwayQualifiers.hasConst() && CastAwayQualifiers.hasVolatile()) {
+ qualifiers = "const and volatile";
+ suffix = "s";
+ } else if (CastAwayQualifiers.hasConst())
+ qualifiers = "const";
+ else if (CastAwayQualifiers.hasVolatile())
+ qualifiers = "volatile";
+ else {
+ llvm_unreachable("Impossible qualifier");
+ }
+ Self.Diag(SrcExpr.get()->getLocStart(), diag::warn_cast_qual) <<
+ TheOffendingSrcType << TheOffendingDestType << qualifiers << suffix;
+ }
}
ExprResult Sema::BuildCStyleCastExpr(SourceLocation LPLoc,
Index: test/Sema/warn-cast-qual.c
===================================================================
--- test/Sema/warn-cast-qual.c (revision 0)
+++ test/Sema/warn-cast-qual.c (working copy)
@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -fsyntax-only -Wcast-qual -verify %s
+
+#include <stdint.h>
+
+void foo() {
+ const char * const ptr = 0;
+ const char * const *ptrptr = 0;
+ char *y = (char *)ptr; // expected-warning {{cast from 'const char *' to 'char *' drops const qualifier}}
+ char **y1 = (char **)ptrptr; // expected-warning {{cast from 'const char *const' to 'char *' drops const qualifier}}
+ const char **y2 = (const char **)ptrptr; // expected-warning {{cast from 'const char *const *' to 'const char **' drops const qualifier}}
+
+ char *z = (char *)(uintptr_t)(const void *)ptr; // no warning
+ char *z1 = (char *)(const void *)ptr; // expected-warning {{cast from 'const void *' to 'char *' drops const qualifier}}
+
+ volatile char *vol = 0;
+ char *vol2 = (char *)vol; // expected-warning {{cast from 'volatile char *' to 'char *' drops volatile qualifier}}
+ const volatile char *volc = 0;
+ char *volc2 = (char *)volc; // expected-warning {{cast from 'const volatile char *' to 'char *' drops const and volatile qualifiers}}
+}
_______________________________________________
cfe-commits mailing list
[email protected]
http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
