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The controlling expression of a _Generic selection expression undergoes lvalue conversion, array conversion, and function conversion before picking the association. This means that array types, function types, and qualified types are all unreachable code if they're used as an association. I've been caught by this twice in the past few months and I figure that if a WG14 member can't seem to remember this rule, users are also likely to struggle with it. So this adds an on-by-default unreachable code diagnostic for generic selection expression associations. Note, we don't have to worry about function types as those are already a constraint violation which generates an error. Differential Revision: https://reviews.llvm.org/D125259
71 lines
4.3 KiB
C
71 lines
4.3 KiB
C
// RUN: %clang_cc1 -std=c11 -fsyntax-only -Wno-strict-prototypes -Wno-implicit-function-declaration -verify %s
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// RUN: %clang_cc1 -std=c99 -pedantic -fsyntax-only -Wno-strict-prototypes -Wno-implicit-function-declaration -verify=expected,ext %s
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void g(void);
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void foo(int n) {
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(void) _Generic(0, // ext-warning {{'_Generic' is a C11 extension}}
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struct A: 0, // expected-error {{type 'struct A' in generic association incomplete}}
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void(): 0, // expected-error {{type 'void ()' in generic association not an object type}}
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int[n]: 0); // expected-error {{type 'int[n]' in generic association is a variably modified type}}
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(void) _Generic(0, // ext-warning {{'_Generic' is a C11 extension}}
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void (*)(): 0, // expected-note {{compatible type 'void (*)()' specified here}}
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void (*)(void): 0); // expected-error {{type 'void (*)(void)' in generic association compatible with previously specified type 'void (*)()'}}
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(void) _Generic((void (*)()) 0, // expected-error {{controlling expression type 'void (*)()' compatible with 2 generic association types}} \
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// ext-warning {{'_Generic' is a C11 extension}}
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void (*)(int): 0, // expected-note {{compatible type 'void (*)(int)' specified here}}
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void (*)(void): 0); // expected-note {{compatible type 'void (*)(void)' specified here}}
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(void) _Generic(0, // expected-error {{controlling expression type 'int' not compatible with any generic association type}} \
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// ext-warning {{'_Generic' is a C11 extension}}
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char: 0, short: 0, long: 0);
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int a1[_Generic(0, int: 1, short: 2, float: 3, default: 4) == 1 ? 1 : -1]; // ext-warning {{'_Generic' is a C11 extension}}
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int a2[_Generic(0, default: 1, short: 2, float: 3, int: 4) == 4 ? 1 : -1]; // ext-warning {{'_Generic' is a C11 extension}}
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int a3[_Generic(0L, int: 1, short: 2, float: 3, default: 4) == 4 ? 1 : -1]; // ext-warning {{'_Generic' is a C11 extension}}
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int a4[_Generic(0L, default: 1, short: 2, float: 3, int: 4) == 1 ? 1 : -1]; // ext-warning {{'_Generic' is a C11 extension}}
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int a5[_Generic(0, int: 1, short: 2, float: 3) == 1 ? 1 : -1]; // ext-warning {{'_Generic' is a C11 extension}}
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int a6[_Generic(0, short: 1, float: 2, int: 3) == 3 ? 1 : -1]; // ext-warning {{'_Generic' is a C11 extension}}
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int a7[_Generic("test", char *: 1, default: 2) == 1 ? 1 : -1]; // ext-warning {{'_Generic' is a C11 extension}}
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int a8[_Generic(g, void (*)(void): 1, default: 2) == 1 ? 1 : -1]; // ext-warning {{'_Generic' is a C11 extension}}
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const int i = 12;
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int a9[_Generic(i, int: 1, default: 2) == 1 ? 1 : -1]; // ext-warning {{'_Generic' is a C11 extension}}
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// This is expected to not trigger any diagnostics because the controlling
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// expression is not evaluated.
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(void)_Generic(*(int *)0, int: 1); // ext-warning {{'_Generic' is a C11 extension}}
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}
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int __attribute__((overloadable)) test (int);
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double __attribute__((overloadable)) test (double);
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char testc(char);
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void PR30201(void) {
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_Generic(4, char:testc, default:test)(4); // ext-warning {{'_Generic' is a C11 extension}}
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}
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void GH50227(void) {
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// Previously, the controlling expression for the outer _Generic makes it
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// result dependent, and testing whether that controlling expression has side
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// effects would cause a crash.
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_Generic( // ext-warning {{'_Generic' is a C11 extension}}
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n(
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_Generic(n++, int : 0) // expected-error {{cannot increment value of type 'int ()'}} ext-warning {{'_Generic' is a C11 extension}}
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), int : 0);
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}
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void unreachable_associations(const int i) {
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_Static_assert( // ext-warning {{'_Static_assert' is a C11 extension}}
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_Generic(i, // ext-warning {{'_Generic' is a C11 extension}}
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const int : 1, // expected-warning {{due to lvalue conversion of the controlling expression, association of type 'const int' will never be selected because it is qualified}}
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volatile int : 2, // expected-warning {{due to lvalue conversion of the controlling expression, association of type 'volatile int' will never be selected because it is qualified}}
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int[12] : 3, // expected-warning {{due to lvalue conversion of the controlling expression, association of type 'int[12]' will never be selected because it is of array type}}
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int : 4,
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default : 5
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) == 4, "we had better pick int!");
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}
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