The last line should have a warning on it (and assuming the expected-warning comments in the test are correct, it doesn't):
GCC 4.9: warning: cast from type 'int**' to type 'const int**' casts away qualifiers [-Wcast-qual] const int **bahc = (const int **)bah; On Tue, Nov 18, 2014 at 6:11 AM, Roman Divacky <[email protected]> wrote: > Scrap the previous patch. It doesnt work when we add qualifiers. The new > version is fixed. > > On Tue, Nov 18, 2014 at 12:49:59PM +0100, Roman Divacky wrote: > > 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}} > > +} > >
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