f786881340
Implement `llvm.coro.await.suspend` intrinsics, to deal with performance regression after prohibiting `.await_suspend` inlining, as suggested in #64945. Actually, there are three new intrinsics, which directly correspond to each of three forms of `await_suspend`: ``` void llvm.coro.await.suspend.void(ptr %awaiter, ptr %frame, ptr @wrapperFunction) i1 llvm.coro.await.suspend.bool(ptr %awaiter, ptr %frame, ptr @wrapperFunction) ptr llvm.coro.await.suspend.handle(ptr %awaiter, ptr %frame, ptr @wrapperFunction) ``` There are three different versions instead of one, because in `bool` case it's result is used for resuming via a branch, and in `coroutine_handle` case exceptions from `await_suspend` are handled in the coroutine, and exceptions from the subsequent `.resume()` are propagated to the caller. Await-suspend block is simplified down to intrinsic calls only, for example for symmetric transfer: ``` %id = call token @llvm.coro.save(ptr null) %handle = call ptr @llvm.coro.await.suspend.handle(ptr %awaiter, ptr %frame, ptr @wrapperFunction) call void @llvm.coro.resume(%handle) %result = call i8 @llvm.coro.suspend(token %id, i1 false) switch i8 %result, ... ``` All await-suspend logic is moved out into a wrapper function, generated for each suspension point. The signature of the function is `<type> wrapperFunction(ptr %awaiter, ptr %frame)` where `<type>` is one of `void` `i1` or `ptr`, depending on the return type of `await_suspend`. Intrinsic calls are lowered during `CoroSplit` pass, right after the split. Because I'm new to LLVM, I'm not sure if the helper function generation, calls to them and lowering are implemented in the right way, especially with regard to various metadata and attributes, i. e. for TBAA. All things that seemed questionable are marked with `FIXME` comments. There is another detail: in case of symmetric transfer raw pointer to the frame of coroutine, that should be resumed, is returned from the helper function and a direct call to `@llvm.coro.resume` is generated. C++ standard demands, that `.resume()` method is evaluated. Not sure how important is this, because code has been generated in the same way before, sans helper function.
54 lines
1.6 KiB
C++
54 lines
1.6 KiB
C++
// The output of O0 is highly redundant and hard to test. Also it is not good
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// limit the output of O0. So we test the optimized output from O0. The idea
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// is the optimizations shouldn't change the semantics of the program.
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// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -std=c++20 \
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// RUN: -O0 -emit-llvm %s -o - -disable-O0-optnone \
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// RUN: | opt -passes='sroa,mem2reg,simplifycfg' -S | FileCheck %s --check-prefix=CHECK-O0
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#include "Inputs/coroutine.h"
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// A simple awaiter type with an await_suspend method that can't be
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// inlined.
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struct Awaiter {
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const int& x;
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bool await_ready() { return false; }
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std::coroutine_handle<> await_suspend(const std::coroutine_handle<> h);
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void await_resume() {}
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};
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struct MyTask {
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// A lazy promise with an await_transform method that supports awaiting
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// integer references using the Awaiter struct above.
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struct promise_type {
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MyTask get_return_object() {
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return MyTask{
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std::coroutine_handle<promise_type>::from_promise(*this),
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};
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}
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std::suspend_always initial_suspend() { return {}; }
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std::suspend_always final_suspend() noexcept { return {}; }
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void unhandled_exception();
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auto await_transform(const int& x) { return Awaiter{x}; }
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};
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std::coroutine_handle<> h;
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};
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// A global array of integers.
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int g_array[32];
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// A coroutine that awaits each integer in the global array.
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MyTask FooBar() {
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for (const int& x : g_array) {
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co_await x;
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}
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}
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// CHECK-O0: define{{.*}}@_Z6FooBarv.resume
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// CHECK-O0: call{{.*}}@__await_suspend_wrapper__Z6FooBarv_await(
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// CHECK-O0-NOT: store
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// CHECK-O0: ret void
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