| Message ID | 20191023181002.GL2922@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | C++ PATCH for c++/91548 - fix detecting modifying const objects for ARRAY_REF | expand |
On 10/23/19 2:10 PM, Marek Polacek wrote: > This fixes a bogus "modifying a const object" error for an array that actually > isn't declared const. The problem was how I handled ARRAY_REFs here; we > shouldn't look at the ARRAY_REF itself, but at the array its accessing. > > Bootstrapped/regtested on x86_64-linux, ok for trunk? OK. > 2019-10-23 Marek Polacek <polacek@redhat.com> > > PR c++/91548 - fix detecting modifying const objects for ARRAY_REF. > * constexpr.c (cxx_eval_store_expression): Don't call > modifying_const_object_p for ARRAY_REF. > > * g++.dg/cpp1y/constexpr-tracking-const15.C: New test. > * g++.dg/cpp1y/constexpr-tracking-const16.C: New test. > * g++.dg/cpp1z/constexpr-tracking-const1.C: New test. > > diff --git gcc/cp/constexpr.c gcc/cp/constexpr.c > index 11a1eaa0e82..6b4e854e35c 100644 > --- gcc/cp/constexpr.c > +++ gcc/cp/constexpr.c > @@ -3910,10 +3910,6 @@ cxx_eval_store_expression (const constexpr_ctx *ctx, tree t, > tree elt = TREE_OPERAND (probe, 1); > if (TREE_CODE (elt) == FIELD_DECL && DECL_MUTABLE_P (elt)) > mutable_p = true; > - if (evaluated > - && modifying_const_object_p (TREE_CODE (t), probe, mutable_p) > - && const_object_being_modified == NULL_TREE) > - const_object_being_modified = probe; > if (TREE_CODE (probe) == ARRAY_REF) > { > elt = eval_and_check_array_index (ctx, probe, false, > @@ -3921,6 +3917,15 @@ cxx_eval_store_expression (const constexpr_ctx *ctx, tree t, > if (*non_constant_p) > return t; > } > + /* We don't check modifying_const_object_p for ARRAY_REFs. Given > + "int a[10]", an ARRAY_REF "a[2]" can be "const int", even though > + the array isn't const. Instead, check "a" in the next iteration; > + that will detect modifying "const int a[10]". */ > + else if (evaluated > + && modifying_const_object_p (TREE_CODE (t), probe, > + mutable_p) > + && const_object_being_modified == NULL_TREE) > + const_object_being_modified = probe; > vec_safe_push (refs, elt); > vec_safe_push (refs, TREE_TYPE (probe)); > probe = ob; > diff --git gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const15.C gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const15.C > new file mode 100644 > index 00000000000..db1b2bb7ea6 > --- /dev/null > +++ gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const15.C > @@ -0,0 +1,21 @@ > +// PR c++/91548 - fix detecting modifying const objects for ARRAY_REF. > +// { dg-do compile { target c++14 } } > + > +constexpr int& impl(const int (&array)[10], int index) { > + return const_cast<int&>(array[index]); > +} > + > +struct A { > + constexpr int& operator[](int i) { return impl(elems, i); } > + int elems[10]; > +}; > + > +constexpr bool > +f() > +{ > + A arr = {}; > + arr[2] = true; > + return false; > +} > + > +constexpr bool b = f(); > diff --git gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const16.C gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const16.C > new file mode 100644 > index 00000000000..5a5b92bc8cc > --- /dev/null > +++ gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const16.C > @@ -0,0 +1,22 @@ > +// PR c++/91548 - fix detecting modifying const objects for ARRAY_REF. > +// { dg-do compile { target c++14 } } > + > +constexpr int& impl(const int (&array)[10], int index) { > + return const_cast<int&>(array[index]); > +} > + > +struct A { > + constexpr int& operator[](int i) { return impl(elems, i); } > + const int elems[10]; > +}; > + > +constexpr bool > +f() > +{ > + A arr = {}; > + arr[2] = 1; // { dg-error "modifying a const object" } > + return false; > +} > + > +constexpr bool b = f(); // { dg-message "in .constexpr. expansion of " } > +// { dg-message "originally declared" "" { target *-*-* } .-1 } > diff --git gcc/testsuite/g++.dg/cpp1z/constexpr-tracking-const1.C gcc/testsuite/g++.dg/cpp1z/constexpr-tracking-const1.C > new file mode 100644 > index 00000000000..a3856b8e7ec > --- /dev/null > +++ gcc/testsuite/g++.dg/cpp1z/constexpr-tracking-const1.C > @@ -0,0 +1,25 @@ > +// PR c++/91548 - fix detecting modifying const objects for ARRAY_REF. > +// { dg-do compile { target c++17 } } > + > +using size_t = decltype(sizeof(0)); > + > +template <typename T, size_t N> > +constexpr T& impl(T const (&array)[N], size_t index) { > + return const_cast<T&>(array[index]); > +} > + > +template <typename T, size_t N> > +struct my_array { > + constexpr T& operator[](size_t i) { return impl(elems, i); } > + constexpr T const& operator[](size_t i) const { return elems[i]; } > + T elems[N]; > +}; > + > +bool f(int i) { > + static constexpr auto table = []() { > + my_array<bool, 256> arr = {}; > + arr[2] = true; > + return arr; > + }(); > + return table[i]; > +} >
diff --git gcc/cp/constexpr.c gcc/cp/constexpr.c index 11a1eaa0e82..6b4e854e35c 100644 --- gcc/cp/constexpr.c +++ gcc/cp/constexpr.c @@ -3910,10 +3910,6 @@ cxx_eval_store_expression (const constexpr_ctx *ctx, tree t, tree elt = TREE_OPERAND (probe, 1); if (TREE_CODE (elt) == FIELD_DECL && DECL_MUTABLE_P (elt)) mutable_p = true; - if (evaluated - && modifying_const_object_p (TREE_CODE (t), probe, mutable_p) - && const_object_being_modified == NULL_TREE) - const_object_being_modified = probe; if (TREE_CODE (probe) == ARRAY_REF) { elt = eval_and_check_array_index (ctx, probe, false, @@ -3921,6 +3917,15 @@ cxx_eval_store_expression (const constexpr_ctx *ctx, tree t, if (*non_constant_p) return t; } + /* We don't check modifying_const_object_p for ARRAY_REFs. Given + "int a[10]", an ARRAY_REF "a[2]" can be "const int", even though + the array isn't const. Instead, check "a" in the next iteration; + that will detect modifying "const int a[10]". */ + else if (evaluated + && modifying_const_object_p (TREE_CODE (t), probe, + mutable_p) + && const_object_being_modified == NULL_TREE) + const_object_being_modified = probe; vec_safe_push (refs, elt); vec_safe_push (refs, TREE_TYPE (probe)); probe = ob; diff --git gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const15.C gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const15.C new file mode 100644 index 00000000000..db1b2bb7ea6 --- /dev/null +++ gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const15.C @@ -0,0 +1,21 @@ +// PR c++/91548 - fix detecting modifying const objects for ARRAY_REF. +// { dg-do compile { target c++14 } } + +constexpr int& impl(const int (&array)[10], int index) { + return const_cast<int&>(array[index]); +} + +struct A { + constexpr int& operator[](int i) { return impl(elems, i); } + int elems[10]; +}; + +constexpr bool +f() +{ + A arr = {}; + arr[2] = true; + return false; +} + +constexpr bool b = f(); diff --git gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const16.C gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const16.C new file mode 100644 index 00000000000..5a5b92bc8cc --- /dev/null +++ gcc/testsuite/g++.dg/cpp1y/constexpr-tracking-const16.C @@ -0,0 +1,22 @@ +// PR c++/91548 - fix detecting modifying const objects for ARRAY_REF. +// { dg-do compile { target c++14 } } + +constexpr int& impl(const int (&array)[10], int index) { + return const_cast<int&>(array[index]); +} + +struct A { + constexpr int& operator[](int i) { return impl(elems, i); } + const int elems[10]; +}; + +constexpr bool +f() +{ + A arr = {}; + arr[2] = 1; // { dg-error "modifying a const object" } + return false; +} + +constexpr bool b = f(); // { dg-message "in .constexpr. expansion of " } +// { dg-message "originally declared" "" { target *-*-* } .-1 } diff --git gcc/testsuite/g++.dg/cpp1z/constexpr-tracking-const1.C gcc/testsuite/g++.dg/cpp1z/constexpr-tracking-const1.C new file mode 100644 index 00000000000..a3856b8e7ec --- /dev/null +++ gcc/testsuite/g++.dg/cpp1z/constexpr-tracking-const1.C @@ -0,0 +1,25 @@ +// PR c++/91548 - fix detecting modifying const objects for ARRAY_REF. +// { dg-do compile { target c++17 } } + +using size_t = decltype(sizeof(0)); + +template <typename T, size_t N> +constexpr T& impl(T const (&array)[N], size_t index) { + return const_cast<T&>(array[index]); +} + +template <typename T, size_t N> +struct my_array { + constexpr T& operator[](size_t i) { return impl(elems, i); } + constexpr T const& operator[](size_t i) const { return elems[i]; } + T elems[N]; +}; + +bool f(int i) { + static constexpr auto table = []() { + my_array<bool, 256> arr = {}; + arr[2] = true; + return arr; + }(); + return table[i]; +}