[PATCH] Fix to PR5683 - issue diagnostic for pointer subtraction with type of size zero.
Serge Pavlov
sepavloff at gmail.com
Tue Aug 27 05:06:02 PDT 2013
C++ tests were moved to SemaCXX, thanks to Eli Friedman for pointing this out.
Hi rsmith,
http://llvm-reviews.chandlerc.com/D637
CHANGE SINCE LAST DIFF
http://llvm-reviews.chandlerc.com/D637?vs=2538&id=3805#toc
Files:
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/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td
+++ include/clang/Basic/DiagnosticSemaKinds.td
@@ -4178,6 +4178,9 @@
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
@@ -6561,6 +6561,14 @@
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()) {
+ Result = APValue(Info.Ctx.MakeIntValue(0, E->getType()));
+ return true;
+ }
+
// 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 +1,17 @@
+// 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}}
+
+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}}
+}
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