clang/test/SemaCXX/attr-likelihood.cpp

   1 // RUN: %clang_cc1 %s -std=c++17 -fsyntax-only -verify
   2 // RUN: %clang_cc1 %s -DPEDANTIC -pedantic -fsyntax-only -verify
   3
   4 #if PEDANTIC
   5 void g() {
   6   if (true)
   7     [[likely]] {} // expected-warning {{use of the 'likely' attribute is a C++20 extension}}
   8   else
   9     [[unlikely]] {} // expected-warning {{use of the 'unlikely' attribute is a C++20 extension}}
  10 }
  11 #else
  12 void a() {
  13   if (true)
  14     [[likely]]; // expected-warning {{conflicting attributes 'likely' are ignored}}
  15   else
  16     [[likely]]; // expected-note {{conflicting attribute is here}}
  17 }
  18
  19 void b() {
  20   if (true)
  21     [[unlikely]]; // expected-warning {{conflicting attributes 'unlikely' are ignored}}
  22   else
  23     [[unlikely]]; // expected-note {{conflicting attribute is here}}
  24 }
  25
  26 void c() {
  27   if (true)
  28     [[likely]];
  29 }
  30
  31 void d() {
  32   if (true)
  33     [[unlikely]];
  34 }
  35
  36 void g() {
  37   if (true)
  38     [[likely]] {}
  39   else
  40     [[unlikely]] {}
  41 }
  42
  43 void h() {
  44   if (true)
  45     [[likely]] {}
  46   else {
  47   }
  48 }
  49
  50 void i() {
  51   if (true)
  52     [[unlikely]] {}
  53   else {
  54   }
  55 }
  56
  57 void j() {
  58   if (true) {
  59   } else
  60     [[likely]] {}
  61 }
  62
  63 void k() {
  64   if (true) {
  65   } else
  66     [[likely]] {}
  67 }
  68
  69 void l() {
  70   if (true)
  71     [[likely]] {}
  72   else
  73     [[unlikely]] if (false) [[likely]] {}
  74 }
  75
  76 void m() {
  77   [[likely]] int x = 42; // expected-error {{'likely' attribute cannot be applied to a declaration}}
  78
  79   if (x)
  80     [[unlikely]] {}
  81   if (x) {
  82     [[unlikely]];
  83   }
  84   switch (x) {
  85   case 1:
  86     [[likely]] {}
  87     break;
  88     [[likely]] case 2 : case 3 : {}
  89     break;
  90   }
  91
  92   do {
  93     [[unlikely]];
  94   } while (x);
  95   do
  96     [[unlikely]] {}
  97   while (x);
  98   do { // expected-note {{to match this 'do'}}
  99   }
 100   [[unlikely]] while (x); // expected-error {{expected 'while' in do/while loop}}
 101   for (;;)
 102     [[unlikely]] {}
 103   for (;;) {
 104     [[unlikely]];
 105   }
 106   while (x)
 107     [[unlikely]] {}
 108   while (x) {
 109     [[unlikely]];
 110   }
 111
 112   switch (x)
 113     [[unlikely]] {}
 114
 115   if (x)
 116     goto lbl;
 117
 118   // FIXME: allow the attribute on the label
 119   [[unlikely]] lbl : // expected-error {{'unlikely' attribute cannot be applied to a declaration}}
 120                      [[likely]] x = x + 1;
 121
 122   [[likely]]++ x;
 123 }
 124
 125 void n() [[likely]] // expected-error {{'likely' attribute cannot be applied to types}}
 126 {
 127   try
 128     [[likely]] {} // expected-error {{expected '{'}}
 129   catch (...) [[likely]] { // expected-error {{expected expression}}
 130   }
 131 }
 132
 133 void o()
 134 {
 135   // expected-warning@+2 {{attribute 'likely' has no effect when annotating an 'if constexpr' statement}}
 136   // expected-note@+1 {{annotating the 'if constexpr' statement here}}
 137   if constexpr (true) [[likely]];
 138
 139   // expected-note@+1 {{annotating the 'if constexpr' statement here}}
 140   if constexpr (true) {
 141   // expected-warning@+1 {{attribute 'unlikely' has no effect when annotating an 'if constexpr' statement}}
 142   } else [[unlikely]];
 143
 144   // Annotating both branches with conflicting likelihoods generates no diagnostic regarding the conflict.
 145   // expected-warning@+2 {{attribute 'likely' has no effect when annotating an 'if constexpr' statement}}
 146   // expected-note@+1 2 {{annotating the 'if constexpr' statement here}}
 147   if constexpr (true) [[likely]] {
 148   // expected-warning@+1 {{attribute 'likely' has no effect when annotating an 'if constexpr' statement}}
 149   } else [[likely]];
 150
 151   if (1) [[likely, unlikely]] { // expected-error {{'unlikely' and 'likely' attributes are not compatible}} \
 152                                 // expected-note {{conflicting attribute is here}}
 153   } else [[unlikely]][[likely]] { // expected-error {{'likely' and 'unlikely' attributes are not compatible}} \
 154                                   // expected-note {{conflicting attribute is here}}
 155   }
 156 }
 157
 158 constexpr int constexpr_function() {
 159   [[likely]] return 0;
 160 }
 161 static_assert(constexpr_function() == 0);
 162
 163 constexpr double pow(double x, long long n) noexcept {
 164     if (n > 0) [[likely]]
 165         return x * pow(x, n - 1);
 166     else [[unlikely]]
 167         return 1;
 168 }
 169 constexpr long long fact(long long n) noexcept {
 170     if (n > 1) [[likely]]
 171         return n * fact(n - 1);
 172     else [[unlikely]]
 173         return 1;
 174 }
 175
 176 #endif