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Constant evaluation of virtual calls to an overrider in a base class [GH #397] #415
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,21 @@ | ||
| [GH #397] | ||
| Constant evaluation of virtual calls to an overrider in a base class | ||
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| During constant evaluation, a virtual function call whose final overrider is | ||
| a member of an intermediate base class (rather than of the most derived | ||
| class) was evaluated with the complete object as the object expression, | ||
| instead of the base class subobject of which the overrider is a member. For | ||
| example, with --c++20: | ||
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| struct A { constexpr virtual int f() const { return 1; } int a = 1; }; | ||
| struct B : A { constexpr int f() const override { return a + 2; } }; | ||
| struct E { int e = 0; }; | ||
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Member
There was a problem hiding this comment. If not required for the example, I'd remove |
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| struct F : E, B {}; | ||
| constexpr int g() { F f; A& r = f; return r.f(); } | ||
| static_assert(g() == 3); // Previously failed. | ||
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| This is now fixed. In addition, the adjustment of the result of a call to | ||
| an overrider with a covariant return type (e.g., from a pointer to a derived | ||
| class to a pointer to its base class) was computed incorrectly, and was | ||
| applied even to a null pointer result (which could cause the front end to | ||
| crash); this is also fixed. | ||
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,13 @@ | ||
| fe_only -DTEST_NUMBER=1 --g++ --c++20 Test_name.c | ||
| "Test_name.c", line 21: error: expression must have a constant value | ||
| constexpr int v = g(); // Error: null pointer argument (previously crashed). | ||
| ^ | ||
| "Test_name.c", line 19: note: attempt to dereference a null pointer | ||
| return __builtin_memcmp(rp.p(), (const X*)&s.z, sizeof(X)); | ||
| ^ | ||
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| "Test_name.c", line 21: warning: variable "v" was declared but never referenced | ||
| constexpr int v = g(); // Error: null pointer argument (previously crashed). | ||
| ^ | ||
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| 1 error detected in the compilation of "Test_name.c". |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1 @@ | ||
| fe_only -DTEST_NUMBER=1 --c++20 Test_name.c |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,21 @@ | ||
| //type:fn | ||
| //options:--g++ --c++20 | ||
| //remark:[GH #397] Null pointer result of a covariant virtual call | ||
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| struct E { int e = 0; }; | ||
| struct X { int x = 7; }; | ||
| struct Y { int y = 0; }; | ||
| struct Z : Y, X {}; | ||
| struct P { constexpr virtual const X* p() const { return nullptr; } }; | ||
| struct S : E, P { | ||
| Z z; | ||
| constexpr const Z* p() const override { return nullptr; } | ||
| }; | ||
| constexpr bool f() { S s; const P& rp = s; return rp.p() == nullptr; } | ||
| static_assert(f()); | ||
| constexpr int g() { | ||
| S s; | ||
| const P& rp = s; | ||
| return __builtin_memcmp(rp.p(), (const X*)&s.z, sizeof(X)); | ||
| } | ||
| constexpr int v = g(); // Error: null pointer argument (previously crashed). |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,68 @@ | ||
| //type:fp | ||
| //options:--c++20 | ||
| //remark:[GH #397] Constant evaluation of a virtual call whose final overrider | ||
| //remark:is a member of an intermediate base class | ||
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| struct A { constexpr virtual int f() const { return 1; } int a = 1; }; | ||
| struct B : A { constexpr int f() const override { return a + 2; } }; | ||
| struct E { int e = 0; }; | ||
| struct F : E, B {}; | ||
| constexpr int g() { F f; A& r = f; return r.f(); } | ||
| static_assert(g() == 3); // Previously failed. | ||
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| struct G : B {}; | ||
| constexpr int h() { G g; A& r = g; return r.f(); } | ||
| static_assert(h() == 3); // Previously failed. | ||
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| struct H : E, G { int x = 5; }; | ||
| constexpr int i() { H h; A& ra = h; B& rb = h; return ra.f() * 10 + rb.f(); } | ||
| static_assert(i() == 33); // Previously failed. | ||
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| struct C : A {}; | ||
| constexpr int j() { C c; A& r = c; return r.f(); } | ||
| static_assert(j() == 1); | ||
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| struct X { int x = 7; }; | ||
| struct Y { int y = 0; }; | ||
| struct Z : Y, X {}; | ||
| struct P { constexpr virtual const X* p() const { return nullptr; } }; | ||
| struct Q : P { Z z; constexpr const Z* p() const override { return &z; } }; | ||
| struct R : E, Q {}; | ||
| constexpr int k() { R r; const P& rp = r; return rp.p()->x; } | ||
| static_assert(k() == 7); | ||
| struct S : E, P { | ||
| Z z; | ||
| bool null; | ||
| constexpr S(bool b) : null(b) {} | ||
| constexpr const Z* p() const override { return null ? nullptr : &z; } | ||
| }; | ||
| constexpr bool l(bool b) { | ||
| S s(b); | ||
| const P& rp = s; | ||
| return b ? rp.p() == nullptr : rp.p() == (const X*)&s.z; | ||
| } | ||
| static_assert(l(false)); // Previously failed. | ||
| static_assert(l(true)); | ||
| struct W : Y, Z {}; | ||
| struct T : Q { W w; constexpr const W* p() const override { return &w; } }; | ||
| struct U : E, T {}; | ||
| constexpr bool m() { | ||
| U u; | ||
| const P& rp = u; | ||
| const Q& rq = u; | ||
| return rp.p() == (const X*)&u.w && rq.p() == (const Z*)&u.w && | ||
| rp.p()->x == 7; | ||
| } | ||
| static_assert(m()); // Previously failed. | ||
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| // A covariant return type whose class is an indirect base class. | ||
| struct V : Y, Z {}; | ||
| struct VV : E, V {}; | ||
| struct I : P { VV vv; constexpr const VV* p() const override { return &vv; } }; | ||
| struct J : E, I {}; | ||
| constexpr bool n() { | ||
| J j; | ||
| const P& rp = j; | ||
| return rp.p() == (const X*)&j.vv && rp.p()->x == 7; | ||
| } | ||
| static_assert(n()); |
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