clang/test/CodeGenCoroutines/pr59221.cpp

   1 // Test for PR59221. Tests the compiler wouldn't misoptimize the final result.
   2 //
   3 // REQUIRES: x86-registered-target
   4 //
   5 // RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -std=c++20 %s -O3 -S -emit-llvm -o - | FileCheck %s
   6
   7 #include "Inputs/coroutine.h"
   8
   9 template <typename T> struct task {
  10         struct promise_type {
  11                 T value{123};
  12                 std::coroutine_handle<> caller{std::noop_coroutine()};
  13
  14                 struct final_awaiter: std::suspend_always {
  15                         auto await_suspend(std::coroutine_handle<promise_type> me) const noexcept {
  16                                 return me.promise().caller;
  17                         }
  18                 };
  19
  20                 constexpr auto initial_suspend() const noexcept {
  21                         return std::suspend_always();
  22                 }
  23                 constexpr auto final_suspend() const noexcept {
  24                         return final_awaiter{};
  25                 }
  26                 auto unhandled_exception() noexcept {
  27                         // ignore
  28                 }
  29                 constexpr void return_value(T v) noexcept {
  30                         value = v;
  31                 }
  32                 constexpr auto & get_return_object() noexcept {
  33                         return *this;
  34                 }
  35         };
  36
  37         using coroutine_handle = std::coroutine_handle<promise_type>;
  38
  39         promise_type & promise{nullptr};
  40
  41         task(promise_type & p) noexcept: promise{p} { }
  42
  43         ~task() noexcept {
  44                 coroutine_handle::from_promise(promise).destroy();
  45         }
  46
  47         auto await_ready() noexcept {
  48         return false;
  49     }
  50
  51     auto await_suspend(std::coroutine_handle<> caller) noexcept {
  52         promise.caller = caller;
  53         return coroutine_handle::from_promise(promise);
  54     }
  55
  56     constexpr auto await_resume() const noexcept {
  57         return promise.value;
  58     }
  59
  60         // non-coroutine access to result
  61         auto get() noexcept {
  62                 const auto handle = coroutine_handle::from_promise(promise);
  63
  64                 if (!handle.done()) {
  65                         handle.resume();
  66                 }
  67
  68         return promise.value;
  69         }
  70 };
  71
  72
  73 static inline auto a() noexcept -> task<int> {
  74         co_return 42;
  75 }
  76
  77 static inline auto test() noexcept -> task<int> {
  78         co_return co_await a();
  79 }
  80
  81 int foo() {
  82         return test().get();
  83 }
  84
  85 // Checks that the store for the result value 42 is not misoptimized out.
  86 // CHECK: define{{.*}}_Z3foov(
  87 // CHECK: store i32 42, ptr %{{.*}}
  88 // CHECK: }