[PATCH] Fix to PR5683 - issue diagnostic for pointer subtraction with type of size zero.
Richard Smith
richard at metafoo.co.uk
Tue Sep 10 14:37:03 PDT 2013
Committed with a few tweaks as r190439.
On Mon, Sep 9, 2013 at 7:20 PM, Serge Pavlov <sepavloff at gmail.com> wrote:
> Friedly ping.
>
>
> 2013/8/30 Serge Pavlov <sepavloff at gmail.com>
>
>> Added giagnostics related to constexpr.
>> Error is produced by the code that expects constexpr. However issuing a
>> message why the
>> expression is not constant is more user friendly. With this patch
>> compiler generates an
>> appropriate note, similar to other cases in expression evaluators.
>> CCEDiag is used to
>> report the message as this is core constant expression violation.
>>
>> Hi rsmith,
>>
>> http://llvm-reviews.chandlerc.com/D637
>>
>> CHANGE SINCE LAST DIFF
>> http://llvm-reviews.chandlerc.com/D637?vs=3863&id=3913#toc
>>
>> Files:
>> include/clang/Basic/DiagnosticASTKinds.td
>> include/clang/Basic/DiagnosticSemaKinds.td
>> lib/AST/ExprConstant.cpp
>> lib/Sema/SemaExpr.cpp
>> test/Sema/empty1.c
>> test/SemaCXX/empty1.cpp
>>
>> Index: include/clang/Basic/DiagnosticASTKinds.td
>> ===================================================================
>> --- include/clang/Basic/DiagnosticASTKinds.td
>> +++ include/clang/Basic/DiagnosticASTKinds.td
>> @@ -139,6 +139,8 @@
>> def warn_integer_constant_overflow : Warning<
>> "overflow in expression; result is %0 with type %1">,
>> InGroup<DiagGroup<"integer-overflow">>;
>> +def note_undefined_is_not_constexpr : Note<"operation with undefined
>> behavior "
>> + "cannot be used in constant expression">;
>>
>> // inline asm related.
>> let CategoryName = "Inline Assembly Issue" in {
>> Index: include/clang/Basic/DiagnosticSemaKinds.td
>> ===================================================================
>> --- include/clang/Basic/DiagnosticSemaKinds.td
>> +++ include/clang/Basic/DiagnosticSemaKinds.td
>> @@ -4179,6 +4179,9 @@
>> def warn_offsetof_non_standardlayout_type : ExtWarn<
>> "offset of on non-standard-layout type %0">, InGroup<InvalidOffsetof>;
>> def err_offsetof_bitfield : Error<"cannot compute offset of bit-field
>> %0">;
>> +def warn_sub_ptr_zero_size_types : Warning<
>> + "subtraction of pointers to type %0 of zero size has undefined
>> behavior">,
>> + InGroup<PointerArith>;
>>
>> def warn_floatingpoint_eq : Warning<
>> "comparing floating point with == or != is unsafe">,
>> Index: lib/AST/ExprConstant.cpp
>> ===================================================================
>> --- lib/AST/ExprConstant.cpp
>> +++ lib/AST/ExprConstant.cpp
>> @@ -6570,6 +6570,17 @@
>> if (!HandleSizeof(Info, E->getExprLoc(), ElementType,
>> ElementSize))
>> return false;
>>
>> + // As an extension, a type may have zero size (empty struct or
>> union in
>> + // C, array of zero length). Meaning of pointer difference in
>> such
>> + // case is unspecified.
>> + if (ElementSize.isZero()) {
>> + // C++11 [expr.const]p2:
>> + // A conditional-expression is a core constant expression
>> unless it
>> + // involves ... an operation that would have undefined
>> behavior...
>> + CCEDiag(E, diag::note_undefined_is_not_constexpr);
>> + return false;
>> + }
>> +
>> // FIXME: LLVM and GCC both compute LHSOffset - RHSOffset at
>> runtime,
>> // and produce incorrect results when it overflows. Such behavior
>> // appears to be non-conforming, but is common, so perhaps we
>> should
>> Index: lib/Sema/SemaExpr.cpp
>> ===================================================================
>> --- lib/Sema/SemaExpr.cpp
>> +++ lib/Sema/SemaExpr.cpp
>> @@ -7040,6 +7040,18 @@
>> LHS.get(), RHS.get()))
>> return QualType();
>>
>> + // The pointee type may have zero size. As an extension, a
>> structure or
>> + // union may have zero size or an array may have zero length. In
>> this
>> + // case subtraction does not make sense.
>> + if (!rpointee->isVoidType() && !rpointee->isFunctionType()) {
>> + CharUnits ElementSize = Context.getTypeSizeInChars(rpointee);
>> + if (ElementSize.isZero()) {
>> + Diag(Loc,diag::warn_sub_ptr_zero_size_types)
>> + << rpointee.getUnqualifiedType()
>> + << LHS.get()->getSourceRange() <<
>> RHS.get()->getSourceRange();
>> + }
>> + }
>> +
>> if (CompLHSTy) *CompLHSTy = LHS.get()->getType();
>> return Context.getPointerDiffType();
>> }
>> Index: test/Sema/empty1.c
>> ===================================================================
>> --- test/Sema/empty1.c
>> +++ test/Sema/empty1.c
>> @@ -36,3 +36,50 @@
>> struct emp_1 f1;
>> union emp_2 f2;
>> };
>> +
>> +
>> +// Checks for pointer subtraction (PR15683)
>> +
>> +struct emp_1* func_1p (struct emp_1* x) {
>> + return x - 5;
>> +}
>> +
>> +int func_1 () {
>> + struct emp_1 v[1];
>> + return v - v; // expected-warning {{subtraction of pointers to type
>> 'struct emp_1' of zero size has undefined behavior}}
>> +}
>> +
>> +int func_2 (struct emp_1* x) {
>> + return 1 + x - x; // expected-warning {{subtraction of pointers to
>> type 'struct emp_1' of zero size has undefined behavior}}
>> +}
>> +
>> +int func_3 (struct emp_1* x, struct emp_1* y) {
>> + return x - y; // expected-warning {{subtraction of pointers to type
>> 'struct emp_1' of zero size has undefined behavior}}
>> +}
>> +
>> +int func_4 (struct emp_1* x, const struct emp_1* y) {
>> + return x - y; // expected-warning {{subtraction of pointers to type
>> 'struct emp_1' of zero size has undefined behavior}}
>> +}
>> +
>> +int func_5 (volatile struct emp_1* x, const struct emp_1* y) {
>> + return x - y; // expected-warning {{subtraction of pointers to type
>> 'struct emp_1' of zero size has undefined behavior}}
>> +}
>> +
>> +int func_6 () {
>> + union emp_2 v[1];
>> + return v - v; // expected-warning {{subtraction of pointers to type
>> 'union emp_2' of zero size has undefined behavior}}
>> +}
>> +
>> +struct A; // expected-note {{forward declaration of 'struct A'}}
>> +
>> +int func_7 (struct A* x, struct A* y) {
>> + return x - y; // expected-error {{arithmetic on a pointer to an
>> incomplete type 'struct A'}}
>> +}
>> +
>> +int func_8 (struct emp_1 (*x)[10], struct emp_1 (*y)[10]) {
>> + return x - y; // expected-warning {{subtraction of pointers to type
>> 'struct emp_1 [10]' of zero size has undefined behavior}}
>> +}
>> +
>> +int func_9 (struct emp_1 (*x)[], struct emp_1 (*y)[]) {
>> + return x - y; // expected-error {{arithmetic on a pointer to an
>> incomplete type 'struct emp_1 []'}}
>> +}
>> Index: test/SemaCXX/empty1.cpp
>> ===================================================================
>> --- /dev/null
>> +++ test/SemaCXX/empty1.cpp
>> @@ -0,0 +1,19 @@
>> +// RUN: %clang_cc1 %s -fsyntax-only -std=c++11 -verify
>> +
>> +int func_1(int (*p1)[0], int (*p2)[0]) {
>> + return p1 - p2; // expected-warning {{subtraction of pointers to type
>> 'int [0]' of zero size has undefined behavior}}
>> +}
>> +
>> +constexpr int (*p1)[0] = 0, (*p2)[0] = 0;
>> +constexpr int k = p2 - p1; // expected-warning {{subtraction of
>> pointers to type 'int [0]' of zero size has undefined behavior}} \
>> + // expected-note {{operation with undefined
>> behavior cannot be used in constant expression}} \
>> + // expected-error {{constexpr variable 'k'
>> must be initialized by a constant expression}}
>> +
>> +constexpr int func_2(int (*x1)[0], int (*x2)[0]) {
>> + return x1 - x2; // expected-warning {{subtraction of pointers to type
>> 'int [0]' of zero size has undefined behavior}}
>> +}
>> +
>> +constexpr int func_3(int (*x1)[0], long (*x2)[0]) {
>> + return x1 - x2; // expected-error {{int (*)[0]' and 'long (*)[0]' are
>> not pointers to compatible types}} \
>> + // expected-warning {{of zero size has undefined
>> behavior}}
>> +}
>>
>
>
>
> --
> Thanks,
> --Serge
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20130910/be9ce447/attachment.html>
More information about the cfe-commits
mailing list