[PATCH] Fix to PR5683 - issue diagnostic for pointer subtraction with type of size zero.
Serge Pavlov
sepavloff at gmail.com
Mon Sep 9 19:20:21 PDT 2013
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
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