[llvm-dev] Coroutine LLVM IR Intrinsics

[Alex Horn via llvm-dev]

I have trouble working with the new coroutines intrinsics. For example, I cannot get the example in the official docs to work [1].

What is the intended way of compiling the example to a binary?

Both the following C file and the corresponding manually written LLVM IR produce fatal errors in the toolchain.

=== C ===

#include <stdio.h>
#include <stdlib.h>
#include <stddef.h>

void *f(int n) {
   __builtin_coro_id(32, 0, 0, 0);
   size_t size = __builtin_coro_size();
   void* alloc = malloc(size);
   int8_t* hdl = __builtin_coro_begin(alloc);
   for(;;) {
     printf("n: %d\n", n++);
     int8_t cleanup = __builtin_coro_suspend(0);
     switch (cleanup) {
       case 0:  continue;
       case 1:  goto CLEANUP;
       default: goto SUSPEND;
     }
   }
CLEANUP:
   __builtin_coro_free(hdl);
SUSPEND:
   __builtin_coro_end(hdl, 0);
   return hdl;
}

int main() {
  void* hdl = f(4);
  __builtin_coro_resume(hdl);
  __builtin_coro_resume(hdl);
  __builtin_coro_destroy(hdl);
  return 0;
}


=== LLVM IR (v7) ===


define i32 @main() {
entry:
  %hdl = call i8* @f(i32 4)
  call void @llvm.coro.resume(i8* %hdl)
  call void @llvm.coro.resume(i8* %hdl)
  call void @llvm.coro.destroy(i8* %hdl)
  ret i32 0
}

define i8* @f(i32 %n) {
entry:
  %id = call token @llvm.coro.id(i32 0, i8* null, i8* null, i8* null)
  %size = call i32 @llvm.coro.size.i32()
  %alloc = call i8* @malloc(i32 %size)
  %hdl = call noalias i8* @llvm.coro.begin(token %id, i8* %alloc)
  br label %loop
loop:
  %n.val = phi i32 [ %n, %entry ], [ %inc, %loop ]
  %inc = mul nsw i32 %n.val, %n.val
  call void @print(i32 %n.val)
  %0 = call i8 @llvm.coro.suspend(token none, i1 false)
  switch i8 %0, label %suspend [i8 0, label %loop
                                i8 1, label %cleanup]
cleanup:
  %mem = call i8* @llvm.coro.free(token %id, i8* %hdl)
  br label %suspend
suspend:
  %unused = call i1 @llvm.coro.end(i8* %hdl, i1 false)
  ret i8* %hdl
}

declare i8* @llvm.coro.free(token, i8*)
declare i32 @llvm.coro.size.i32()
declare i8  @llvm.coro.suspend(token, i1)
declare void @llvm.coro.resume(i8*)
declare void @llvm.coro.destroy(i8*)

declare token @llvm.coro.id(i32, i8*, i8*, i8*)
declare i1 @llvm.coro.alloc(token)
declare i8* @llvm.coro.begin(token, i8*)
declare i1 @llvm.coro.end(i8*, i1)

declare noalias i8* @malloc(i32)
declare void @print(i32)
declare void @free(i8*)


I compiled the former with clang -fcoroutines-ts gen.c, whereas the latter was transformed with opt -enable-coroutines -S gen_manual.ll -coro-early -coro-split -o opt.ll followed by an llc -filetype=obj.

In both cases, I used the most recent LLVM 7.0 release, but got fatal errors, e.g., “error in backend: Cannot select: intrinsic %llvm.coro.begin”.

Is there a complete end-to-end example that illustrates the compilation of a small coroutine example written in LLVM IR to a binary?

Many thanks in advance!

- Alex

[1] https://llvm.org/docs/Coroutines.html <https://llvm.org/docs/Coroutines.html>
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