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145
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1 // PR c++/91353 - P1331R2: Allow trivial default init in constexpr contexts.
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2 // { dg-do compile { target c++2a } }
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3 // Test basic use.
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4
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5 struct S {
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6 int i;
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7 constexpr S(bool b) {
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8 if (b)
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9 i = 42;
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10 }
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11 };
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12 constexpr S s1(true);
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13 constexpr S s2(false); // { dg-error "not a constant expression" }
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14
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15 constexpr int
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16 fn1 (int x)
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17 {
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18 int a;
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19 a = 5;
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20 return x + a;
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21 }
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22
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23 static_assert (fn1 (2) == 7);
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24
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25 constexpr int
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26 fn2 (int x)
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27 {
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28 const int a; // { dg-error "uninitialized .const a." }
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29 constexpr int b; // { dg-error "uninitialized .const b." }
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30 return x;
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31 }
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32
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33 constexpr int
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34 fn3 (int x)
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35 {
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36 int a; // { dg-message ".int a. is not const" }
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37 return x + a; // { dg-error "the value of .a. is not usable in a constant expression" }
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38 }
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39
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40 constexpr int a = fn3 (5); // { dg-message "in .constexpr. expansion of" }
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41
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42 constexpr int
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43 fn4 ()
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44 {
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45 struct S { int a = -5; int b; } s;
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46 return s.a;
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47 }
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48
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49 static_assert (fn4 () == -5);
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50
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51 constexpr int
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52 fn5 ()
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53 {
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54 struct S { int a = 9; int b; } s;
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55 return s.b;
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56 }
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57
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58 constexpr int b = fn5 (); // { dg-error "accessing uninitialized member" }
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59 // { dg-message "in .constexpr. expansion of" "" { target *-*-* } .-1 }
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60
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61 constexpr int
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62 fn6 ()
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63 {
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64 int a;
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65 return 42;
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66 }
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67
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68 static_assert (fn6 () == 42);
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69
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70 constexpr int
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71 fn7 (bool b)
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72 {
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73 int a; // { dg-message ".int a. is not const" }
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74 if (b)
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75 a = 42;
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76 return a;
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77 }
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78
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79 static_assert (fn7 (true) == 42);
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80 static_assert (fn7 (false) == 42); // { dg-error "non-constant condition|the value of .a. is not usable" }
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81 // { dg-message "in .constexpr. expansion of" "" { target *-*-* } .-1 }
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82
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83 constexpr int
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84 fn8 (int n)
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85 {
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86 int r;
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87 switch (n)
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88 {
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89 case 1:
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90 r = n;
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91 return r;
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92 case 42:
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93 r = n;
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94 return r;
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95 }
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96 }
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97
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98 static_assert (fn8 (1) == 1);
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99 static_assert (fn8 (42) == 42);
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