[Coroutines]: Part6b: Add coro.id intrinsic.

[GorNishanov]

Summary

1. Make coroutine representation more robust against optimization that may duplicate instruction by introducing coro.id intrinsics that returns a token that will get fed into coro.alloc and coro.begin. Due to coro.id returning a token, it won't get duplicated and can be used as reliable indicator of coroutine identify when a particular coroutine call gets inlined.
2. Move last three arguments of coro.begin into coro.id as they will be shared if coro.begin will get duplicated.
3. doc + test + code updated to support the new intrinsic.

[majnemer]

LGTM with nits addressed

docs/Coroutines.rst

925

optimization

[GorNishanov]

A lot of churn, needs a review.

[GorNishanov]

s/optimizatoin/optimization

[majnemer]

docs/Coroutines.rst

117–122

We should probably say something about coro.id here.

426

Missing the token.

lib/Transforms/Coroutines/CoroEarly.cpp

55–60

Did you intend to send this part out for review?

lib/Transforms/Coroutines/CoroElide.cpp

117

This could just be auto *False = ConstantInt::getFalse(C)

164–166

Hmm... Is it possible for a coro.subfn to use a coro.begin via something weird like a phi?

[GorNishanov]

lib/Transforms/Coroutines/CoroEarly.cpp

55–60

No. I'll take it out. It is for the next patch.

lib/Transforms/Coroutines/CoroElide.cpp

117

Cool! I'll switch to that.

164–166

Sure, but, in that case, it would mean that the handle to coroutine escaped, moved out, was zero out and thus is not eligible for devirtualization.

[GorNishanov]

Feedback addressed. Preparing for landing.

1. Fixes in Coroutines.rst
2. use ConstantInt::getFalse
3. remove commented out code
4. add clarification comment about coro.subfn.addr

docs/Coroutines.rst

 and 6 after which the coroutine will be destroyed.
 
 The LLVM IR for this coroutine looks like this:
 
 .. code-block:: none
 
   define i8* @f(i32 %n) {
   entry:
+    %id = call token @llvm.coro.id(i32 0, i8* null, i8* null)
     %size = call i32 @llvm.coro.size.i32()
     %alloc = call i8* @malloc(i32 %size)
-    %beg = call token @llvm.coro.begin(i8* %alloc, i8* null, i32 0, i8* null, i8* null)
-    %hdl = call noalias i8* @llvm.coro.frame(token %beg)
+    %hdl = call noalias i8* @llvm.coro.begin(token %id, i8* %alloc)
     br label %loop
   loop:
     %n.val = phi i32 [ %n, %entry ], [ %inc, %loop ]
     %inc = add nsw i32 %n.val, 1
     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(i8* %hdl)
     call void @free(i8* %mem)
     br label %suspend
   suspend:
     call void @llvm.coro.end(i8* %hdl, i1 false)
     ret i8* %hdl
   }
 
 The `entry` block establishes the coroutine frame. The `coro.size`_ intrinsic is
 lowered to a constant representing the size required for the coroutine frame. 
-The `coro.begin`_ intrinsic initializes the coroutine frame and returns the a
-token that is used to obtain the coroutine handle via `coro.frame` intrinsic.
-The first parameter of `coro.begin` is given a block of memory to be used if the
-coroutine frame needs to be allocated dynamically.
+The `coro.begin`_ intrinsic initializes the coroutine frame and returns the 
+coroutine handle. The second parameter of `coro.begin` is given a block of memory 
+to be used if the coroutine frame needs to be allocated dynamically.
 
 The `cleanup` block destroys the coroutine frame. The `coro.free`_ intrinsic, 
 given the coroutine handle, returns a pointer of the memory block to be freed or
 `null` if the coroutine frame was not allocated dynamically. The `cleanup` 
 block is entered when coroutine runs to completion by itself or destroyed via
 call to the `coro.destroy`_ intrinsic.
 
 The `suspend` block contains code to be executed when coroutine runs to 
 completion or suspended. The `coro.end`_ intrinsic marks the point where 

 After resume and destroy parts are outlined, function `f` will contain only the 
 code responsible for creation and initialization of the coroutine frame and 
 execution of the coroutine until a suspend point is reached:
 
 .. code-block:: none
 
   define i8* @f(i32 %n) {
   entry:
+    %id = call token @llvm.coro.id(i32 0, i8* null, i8* null)
     %alloc = call noalias i8* @malloc(i32 24)
-    %beg = call token @llvm.coro.begin(i8* %alloc, i8* null, i32 0, i8* null, i8* null)
-    %0 = call i8* @llvm.coro.frame(token %beg)
+    %0 = call noalias i8* @llvm.coro.begin(token %id, i8* %alloc)
     %frame = bitcast i8* %0 to %f.frame*
     %1 = getelementptr %f.frame, %f.frame* %frame, i32 0, i32 0
     store void (%f.frame*)* @f.resume, void (%f.frame*)** %1
     %2 = getelementptr %f.frame, %f.frame* %frame, i32 0, i32 1
     store void (%f.frame*)* @f.destroy, void (%f.frame*)** %2
    
     %inc = add nsw i32 %n, 1
     %inc.spill.addr = getelementptr inbounds %f.Frame, %f.Frame* %FramePtr, i32 0, i32 2

  
 A particular coroutine usage pattern, which is illustrated by the `main` 
 function in the overview section, where a coroutine is created, manipulated and 
 destroyed by the same calling function, is common for coroutines implementing
 RAII idiom and is suitable for allocation elision optimization which avoid 
 dynamic allocation by storing the coroutine frame as a static `alloca` in its 
 caller.
 
-In the entry block, we will call `coro.alloc`_ intrinsic that will return `null`
-when dynamic allocation is required, and an address of an alloca on the caller's
-frame where coroutine frame can be stored if dynamic allocation is elided.
+In the entry block, we will call `coro.alloc`_ intrinsic that will return `true`
+when dynamic allocation is required, and `false` if dynamic allocation is 
+elided.
 
 .. code-block:: none
 
   entry:
-    %elide = call i8* @llvm.coro.alloc()
-    %need.dyn.alloc = icmp ne i8* %elide, null
-    br i1 %need.dyn.alloc, label %coro.begin, label %dyn.alloc
+    %id = call token @llvm.coro.id(i32 0, i8* null, i8* null)
+    %need.dyn.alloc = call i1 @llvm.coro.alloc(token %id)
+    br i1 %need.dyn.alloc, label %dyn.alloc, label %coro.begin
   dyn.alloc:
     %size = call i32 @llvm.coro.size.i32()
     %alloc = call i8* @CustomAlloc(i32 %size)
     br label %coro.begin
   coro.begin:
-    %phi = phi i8* [ %elide, %entry ], [ %alloc, %dyn.alloc ]
-    %beg = call token @llvm.coro.begin(i8* %phi, i8* null, i32 0, i8* null, i8* null)
+    %phi = phi i8* [ null, %entry ], [ %alloc, %dyn.alloc ]
+    %hdl = call noalias i8* @llvm.coro.begin(token %id, i8* %phi)
 
 In the cleanup block, we will make freeing the coroutine frame conditional on
 `coro.free`_ intrinsic. If allocation is elided, `coro.free`_ returns `null`
 thus skipping the deallocation code:
 
 .. code-block:: llvm
 
   cleanup:

 
 .. _coroutine promise:
 
 Coroutine Promise
 -----------------
 
 A coroutine author or a frontend may designate a distinguished `alloca` that can
 be used to communicate with the coroutine. This distinguished alloca is called
-**coroutine promise** and is provided as a third parameter to the `coro.begin`_ 
-intrinsic.
+**coroutine promise** and is provided as the second parameter to the 
+`coro.id`_ intrinsic.
 
 The following coroutine designates a 32 bit integer `promise` and uses it to
 store the current value produced by a coroutine.
 
 .. code-block:: text
 
   define i8* @f(i32 %n) {
   entry:
     %promise = alloca i32
     %pv = bitcast i32* %promise to i8*
-    %elide = call i8* @llvm.coro.alloc()
-    %need.dyn.alloc = icmp ne i8* %elide, null
-    br i1 %need.dyn.alloc, label %coro.begin, label %dyn.alloc
+    %id = call token @llvm.coro.id(i32 0, i8* %pv, i8* null)
+    %need.dyn.alloc = call i1 @llvm.coro.alloc(token %id)
+    br i1 %need.dyn.alloc, label %dyn.alloc, label %coro.begin
   dyn.alloc:
     %size = call i32 @llvm.coro.size.i32()
     %alloc = call i8* @malloc(i32 %size)
     br label %coro.begin
   coro.begin:
-    %phi = phi i8* [ %elide, %entry ], [ %alloc, %dyn.alloc ]
-    %beg = call token @llvm.coro.begin(i8* %phi, i8* %elide, i32 0, i8* %pv, i8* null)
-    %hdl = call i8* @llvm.coro.frame(token %beg)
+    %phi = phi i8* [ null, %entry ], [ %alloc, %dyn.alloc ]
+    %hdl = call noalias i8* @llvm.coro.begin(i8* %phi)
     br label %loop
   loop:
     %n.val = phi i32 [ %n, %coro.begin ], [ %inc, %loop ]
     %inc = add nsw i32 %n.val, 1
     store i32 %n.val, i32* %promise
     %0 = call i8 @llvm.coro.suspend(token none, i1 false)
     switch i8 %0, label %suspend [i8 0, label %loop
                                   i8 1, label %cleanup]

 """"""""
 
 .. code-block:: text
 
   define i8* @f(i32 %n) {
   entry:
     %promise = alloca i32
     %pv = bitcast i32* %promise to i8*
+    ; the second argument to coro.id points to the coroutine promise.
+    %id = call token @llvm.coro.id(i32 0, i8* %pv, i8* null)
     ...
-    ; the fourth argument to coro.begin points to the coroutine promise.
-    %beg = call token @llvm.coro.begin(i8* %alloc, i8* null, i32 0, i8* %pv, i8* null)
-    %hdl = call noalias i8* @llvm.coro.frame(token %beg)
+    %hdl = call noalias i8* @llvm.coro.begin(token %id, i8* %alloc)
     ...
     store i32 42, i32* %promise ; store something into the promise
     ...
     ret i8* %hdl
   }
 
   define i32 @main() {
   entry:

 the coroutine frame. 
 
 .. _coro.begin:
 
 'llvm.coro.begin' Intrinsic
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 ::
 
-  declare i8* @llvm.coro.begin(i8* <mem>, i8* <elide>, i32 <align>, i8* <promise>, i8* <fnaddr>)
+  declare i8* @llvm.coro.begin(token <id>, i8* <mem>)
 
 Overview:
 """""""""
 
-The '``llvm.coro.begin``' intrinsic captures coroutine initialization 
-information and returns a token that can be used by `coro.frame` intrinsic to
-return an address of the coroutine frame.
+The '``llvm.coro.begin``' intrinsic returns an address of the coroutine frame.
 
 Arguments:
 """"""""""
 
-The first argument is a pointer to a block of memory where coroutine frame
-will be stored.
+The first argument is a token returned by a call to '``llvm.coro.id``' 
+identifying the coroutine.
 
-The second argument is either null or an SSA value of `coro.alloc` intrinsic.
-
-The third argument provides information on the alignment of the memory returned 
-by the allocation function and given to `coro.begin` by the first argument. If 
-this argument is 0, the memory is assumed to be aligned to 2 * sizeof(i8*).
-This argument only accepts constants.
-
-The fourth argument, if not `null`, designates a particular alloca instruction to
-be a `coroutine promise`_.
-
-The fifth argument is `null` before coroutine is split, and later is replaced 
-to point to a private global constant array containing function pointers to 
-outlined resume and destroy parts of the coroutine.
+The second argument is a pointer to a block of memory where coroutine frame
+will be stored if it is allocated dynamically.
 
 Semantics:
 """"""""""
 
 Depending on the alignment requirements of the objects in the coroutine frame
-and/or on the codegen compactness reasons the pointer returned from `coro.frame`
-associated with a particular `coro.begin` may be at offset to the `%mem` 
-argument. (This could be beneficial if instructions that express relative access
-to data can be more compactly encoded with small positive and negative offsets).
+and/or on the codegen compactness reasons the pointer returned from `coro.begin` 
+may be at offset to the `%mem` argument. (This could be beneficial if 
+instructions that express relative access to data can be more compactly encoded 
+with small positive and negative offsets).
 
 A frontend should emit exactly one `coro.begin` intrinsic per coroutine.
 
 .. _coro.free:
 
 'llvm.coro.free' Intrinsic
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 ::
 
   declare i8* @llvm.coro.free(i8* <frame>)
 
 Overview:
 """""""""
 
 The '``llvm.coro.free``' intrinsic returns a pointer to a block of memory where 
 coroutine frame is stored or `null` if this instance of a coroutine did not use
 dynamically allocated memory for its coroutine frame.
 
 Arguments:
 """"""""""
 
 A pointer to the coroutine frame. This should be the same pointer that was 
-returned by prior `coro.frame` call.
+returned by prior `coro.begin` call.
 
 Example (custom deallocation function):
 """""""""""""""""""""""""""""""""""""""
 
 .. code-block:: llvm
 
   cleanup:
     %mem = call i8* @llvm.coro.free(i8* %frame)
cleanup:
     ret void
 
 .. _coro.alloc:
 
 'llvm.coro.alloc' Intrinsic
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 ::
 
-  declare i8* @llvm.coro.alloc()
+  declare i1 @llvm.coro.alloc(token <id>)
 
 Overview:
 """""""""
 
-The '``llvm.coro.alloc``' intrinsic returns an address of the memory on the 
-callers frame where coroutine frame of this coroutine can be placed or `null` 
-otherwise.
+The '``llvm.coro.alloc``' intrinsic returns `true` if dynamic allocation is
+required to obtain a memory for the corutine frame and `false` otherwise.
 
 Arguments:
 """"""""""
 
-None
+The first argument is a token returned by a call to '``llvm.coro.id``' 
+identifying the coroutine.
 
 Semantics:
 """"""""""
 
-If the coroutine is eligible for heap elision, this intrinsic is lowered to an 
-alloca storing the coroutine frame. Otherwise, it is lowered to constant `null`.
-
 A frontend should emit at most one `coro.alloc` intrinsic per coroutine.
-
-If `coro.alloc` is present, the second parameter to `coro.begin` should refer 
-to it.
+The intrinsic is used to suppress dynamic allocation of the coroutine frame
+when possible.
 
 Example:
 """"""""
 
 .. code-block:: text
 
   entry:
-    %elide = call i8* @llvm.coro.alloc()
-    %0 = icmp ne i8* %elide, null
-    br i1 %0, label %coro.begin, label %coro.alloc
+    %id = call token @llvm.coro.id(i32 0, i8* null, i8* null)
+    %dyn.alloc.required = call i1 @llvm.coro.alloc(token %id)
+    br i1 %dyn.alloc.required, label %coro.alloc, label %coro.begin
 
   coro.alloc:
     %frame.size = call i32 @llvm.coro.size()
     %alloc = call i8* @MyAlloc(i32 %frame.size)
     br label %coro.begin
 
   coro.begin:
-    %phi = phi i8* [ %elide, %entry ], [ %alloc, %coro.alloc ]
-    %beg = call token @llvm.coro.begin(i8* %phi, i8* %elide, i32 0, i8* null, i8* null)
-    %frame = call i8* @llvm.coro.frame(token %beg)
+    %phi = phi i8* [ null, %entry ], [ %alloc, %coro.alloc ]
+    %frame = call i8* @llvm.coro.begin(token %id, i8* %phi)
 
 .. _coro.frame:
 
 'llvm.coro.frame' Intrinsic
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 ::
 
   declare i8* @llvm.coro.frame()
 
 Overview:
 """""""""
 
 The '``llvm.coro.frame``' intrinsic returns an address of the coroutine frame of
 the enclosing coroutine.
 
 Arguments:
 """"""""""
 
-A token that refers to `coro.begin` instruction.
+None
+
+Semantics:
+""""""""""
+
+This intrinsic is lowered to refer to the `coro.begin`_ instruction. This is
+a frontend convenience intrinsic that makes it easier to refer to the
+coroutine frame.
+
+.. _coro.id:
+
+'llvm.coro.id' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+::
+
+  declare token @llvm.coro.id(i32 <align>, i8* <promise>, i8* <fnaddr>)
+
+Overview:
+"""""""""
+
+The '``llvm.coro.id``' intrinsic returns a token identifying a coroutine.
+
+Arguments:
+""""""""""
+
+The first argument provides information on the alignment of the memory returned 
+by the allocation function and given to `coro.begin` by the first argument. If 
+this argument is 0, the memory is assumed to be aligned to 2 * sizeof(i8*).
+This argument only accepts constants.
+
+The second argument, if not `null`, designates a particular alloca instruction
+to be a `coroutine promise`_.
+
+The third argument is `null` before coroutine is split, and later is replaced 
+to point to a private global constant array containing function pointers to 
+outlined resume and destroy parts of the coroutine.
+
 
 Semantics:
 """"""""""
 
-This intrinsic is lowered to refer to address of the coroutine frame. 
+The purpose of this intrinsic is to tie together `coro.id`, `coro.alloc` and
+`coro.begin` belonging to the same coroutine to prevent optimizatoin passes from
+duplicating any of these instructions unless entire body of the coroutine is
+duplicated.
+
+A frontend should emit exactly one `coro.id` intrinsic per coroutine.
 
 .. _coro.end:
 
 'llvm.coro.end' Intrinsic
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 ::
 
   declare void @llvm.coro.end(i8* <handle>, i1 <unwind>)

 CoroSplit
 ---------
 The pass CoroSplit buides coroutine frame and outlines resume and destroy parts 
 into separate functions.
 
 CoroElide
 ---------
 The pass CoroElide examines if the inlined coroutine is eligible for heap 
-allocation elision optimization. If so, it replaces `coro.alloc` and 
-`coro.frame` intrinsic with an address of a coroutine frame placed on its caller
-and replaces `coro.free` intrinsics with `null` to remove the deallocation code. 
+allocation elision optimization. If so, it replaces 
+`coro.begin` intrinsic with an address of a coroutine frame placed on its caller
+and replaces `coro.alloc` and `coro.free` intrinsics with `false` and `null`
+respectively to remove the deallocation code. 
 This pass also replaces `coro.resume` and `coro.destroy` intrinsics with direct 
 calls to resume and destroy functions for a particular coroutine where possible.
 
 CoroCleanup
 -----------
 This pass runs late to lower all coroutine related intrinsics not replaced by
 earlier passes.
 

include/llvm/IR/Intrinsics.td

def int_experimental_gc_relocate : Intrinsic<[llvm_any_ty],
                                 [llvm_token_ty, llvm_i32_ty, llvm_i32_ty],
                                 [IntrReadMem]>;
 
 //===------------------------ Coroutine Intrinsics ---------------===//
 // These are documented in docs/Coroutines.rst
 
 // Coroutine Structure Intrinsics.
 
-def int_coro_alloc : Intrinsic<[llvm_ptr_ty], [], []>;
-def int_coro_begin : Intrinsic<[llvm_token_ty], [llvm_ptr_ty, llvm_ptr_ty, 
-                                llvm_i32_ty, llvm_ptr_ty, llvm_ptr_ty],
-                               [WriteOnly<0>, WriteOnly<0>, 
-                                ReadNone<3>, ReadOnly<4>, NoCapture<4>]>;
+def int_coro_id : Intrinsic<[llvm_token_ty], [llvm_i32_ty, llvm_ptr_ty, 
+                             llvm_ptr_ty], 
+                            [IntrArgMemOnly, IntrReadMem, 
+                             ReadNone<1>, ReadOnly<2>, NoCapture<2>]>;
+def int_coro_alloc : Intrinsic<[llvm_i1_ty], [llvm_token_ty], []>;
+def int_coro_begin : Intrinsic<[llvm_ptr_ty], [llvm_token_ty, llvm_ptr_ty],
+                               [WriteOnly<1>]>;
 
 def int_coro_free : Intrinsic<[llvm_ptr_ty], [llvm_ptr_ty],
                               [IntrArgMemOnly, ReadOnly<0>, NoCapture<0>]>;
 def int_coro_end : Intrinsic<[], [llvm_ptr_ty, llvm_i1_ty], []>;
 
-def int_coro_frame : Intrinsic<[llvm_ptr_ty], [llvm_token_ty], [IntrNoMem]>;
+def int_coro_frame : Intrinsic<[llvm_ptr_ty], [], [IntrNoMem]>;
 def int_coro_size : Intrinsic<[llvm_anyint_ty], [], [IntrNoMem]>;
 
 def int_coro_save : Intrinsic<[llvm_token_ty], [llvm_ptr_ty], []>;
 def int_coro_suspend : Intrinsic<[llvm_i8_ty], [llvm_token_ty, llvm_i1_ty], []>;
 
 def int_coro_param : Intrinsic<[llvm_i1_ty], [llvm_ptr_ty, llvm_ptr_ty],
                                [IntrNoMem, ReadNone<0>, ReadNone<1>]>;
 

lib/IR/Verifier.cpp

void Verifier::visitIntrinsicCallSite(Intrinsic::ID ID, CallSite CS) {
   // or are local to *this* function.
   for (Value *V : CS.args()) 
     if (auto *MD = dyn_cast<MetadataAsValue>(V))
       visitMetadataAsValue(*MD, CS.getCaller());
 
   switch (ID) {
   default:
     break;
-  case Intrinsic::coro_begin: {
-    auto *InfoArg = CS.getArgOperand(3)->stripPointerCasts();
+  case Intrinsic::coro_id: {
+    auto *InfoArg = CS.getArgOperand(2)->stripPointerCasts();
     if (isa<ConstantPointerNull>(InfoArg))
       break;
     auto *GV = dyn_cast<GlobalVariable>(InfoArg);
     Assert(GV && GV->isConstant() && GV->hasDefinitiveInitializer(),
       "info argument of llvm.coro.begin must refer to an initialized "
       "constant");
     Constant *Init = GV->getInitializer();
     Assert(isa<ConstantStruct>(Init) || isa<ConstantArray>(Init),

lib/Transforms/Coroutines/CoroEarly.cpp

 bool Lowerer::lowerEarlyIntrinsics(Function &F) {
   bool Changed = false;
   for (auto IB = inst_begin(F), IE = inst_end(F); IB != IE;) {
     Instruction &I = *IB++;
     if (auto CS = CallSite(&I)) {
       switch (CS.getIntrinsicID()) {
       default:
         continue;
-      case Intrinsic::coro_begin:
+      // case Intrinsic::coro_alloc:
+      // case Intrinsic::coro_begin:
+      //   CS.setCannotDuplicate();
+      //   break;
+      case Intrinsic::coro_id:
         // Mark a function that comes out of the frontend that has a coro.begin
         // with a coroutine attribute.
-        if (auto *CB = cast<CoroBeginInst>(&I)) {
-          if (CB->getInfo().isPreSplit())
+        if (auto *CII = cast<CoroIdInst>(&I)) {
+          if (CII->getInfo().isPreSplit())
             F.addFnAttr(CORO_PRESPLIT_ATTR, UNPREPARED_FOR_SPLIT);
         }
         break;
       case Intrinsic::coro_resume:
         lowerResumeOrDestroy(CS, CoroSubFnInst::ResumeIndex);
         break;
       case Intrinsic::coro_destroy:
         lowerResumeOrDestroy(CS, CoroSubFnInst::DestroyIndex);

lib/Transforms/Coroutines/CoroElide.cpp

 #include "llvm/IR/InstIterator.h"
 #include "llvm/Pass.h"
 #include "llvm/Support/ErrorHandling.h"
 
 using namespace llvm;
 
 #define DEBUG_TYPE "coro-elide"
 
-//===----------------------------------------------------------------------===//
-//                              Top Level Driver
-//===----------------------------------------------------------------------===//
-
-namespace {
-struct CoroElide : FunctionPass {
-  static char ID;
-  CoroElide() : FunctionPass(ID) {}
-
-  bool NeedsToRun = false;
+// Created on demand if CoroElide pass has work to do.
+struct Lowerer : coro::LowererBase {
+  SmallVector<CoroIdInst *, 4> CoroIds;
+  SmallVector<CoroBeginInst *, 1> CoroBegins;
+  SmallVector<CoroAllocInst *, 1> CoroAllocs;
+  SmallVector<CoroSubFnInst *, 4> ResumeAddr;
+  SmallVector<CoroSubFnInst *, 4> DestroyAddr;
+  SmallVector<CoroFreeInst *, 1> CoroFrees;
 
-  bool doInitialization(Module &M) override {
-    NeedsToRun = coro::declaresIntrinsics(M, {"llvm.coro.begin"});
-    return false;
-  }
+  Lowerer(Module &M) : LowererBase(M) {}
 
-  bool runOnFunction(Function &F) override;
-  void getAnalysisUsage(AnalysisUsage &AU) const override {
-    AU.addRequired<AAResultsWrapperPass>();
-    AU.setPreservesCFG();
-  }
+  void elideHeapAllocations(Function *F, Type *FrameTy, AAResults &AA);
+  bool processCoroId(CoroIdInst *, AAResults &AA);
 };
-}
-
-char CoroElide::ID = 0;
-INITIALIZE_PASS_BEGIN(
-    CoroElide, "coro-elide",
-    "Coroutine frame allocation elision and indirect calls replacement", false,
-    false)
-INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
-INITIALIZE_PASS_END(
-    CoroElide, "coro-elide",
-    "Coroutine frame allocation elision and indirect calls replacement", false,
-    false)
-
-Pass *llvm::createCoroElidePass() { return new CoroElide(); }
-
-//===----------------------------------------------------------------------===//
-//                              Implementation
-//===----------------------------------------------------------------------===//
 
 // Go through the list of coro.subfn.addr intrinsics and replace them with the
 // provided constant.
 static void replaceWithConstant(Constant *Value,
                                 SmallVectorImpl<CoroSubFnInst *> &Users) {
   if (Users.empty())
     return;
 
static Instruction *getFirstNonAllocaInTheEntryBlock(Function *F) {
   for (Instruction &I : F->getEntryBlock())
     if (!isa<AllocaInst>(&I))
       return &I;
   llvm_unreachable("no terminator in the entry block");
 }
 
 // To elide heap allocations we need to suppress code blocks guarded by
 // llvm.coro.alloc and llvm.coro.free instructions.
-static void elideHeapAllocations(CoroBeginInst *CoroBegin, Type *FrameTy,
-                                 CoroAllocInst *AllocInst, AAResults &AA) {
-  LLVMContext &C = CoroBegin->getContext();
-  auto *InsertPt = getFirstNonAllocaInTheEntryBlock(CoroBegin->getFunction());
+void Lowerer::elideHeapAllocations(Function *F, Type *FrameTy, AAResults &AA) {
+  LLVMContext &C = FrameTy->getContext();
+  auto *InsertPt =
+      getFirstNonAllocaInTheEntryBlock(CoroIds.front()->getFunction());
+
+  // Replacing llvm.coro.alloc with false will suppress dynamic
+  // allocation as it is expected for the frontend to generate the code that
+  // looks like:
+  //   id = coro.id(...)
+  //   mem = coro.alloc(id) ? malloc(coro.size()) : 0;
+  //   coro.begin(id, mem)
+  auto *False = ConstantInt::get(Type::getInt1Ty(C), 0);
+  for (auto *CA : CoroAllocs) {
+    CA->replaceAllUsesWith(False);
+    CA->eraseFromParent();
+  }
+
+  // To suppress deallocation code, we replace all llvm.coro.free intrinsics
+  // associated with this coro.begin with null constant.
+  auto *NullPtr = ConstantPointerNull::get(Type::getInt8PtrTy(C));
+  for (auto *CF : CoroFrees) {
+    CF->replaceAllUsesWith(NullPtr);
+    CF->eraseFromParent();
+  }
 
   // FIXME: Design how to transmit alignment information for every alloca that
   // is spilled into the coroutine frame and recreate the alignment information
   // here. Possibly we will need to do a mini SROA here and break the coroutine
   // frame into individual AllocaInst recreating the original alignment.
   auto *Frame = new AllocaInst(FrameTy, "", InsertPt);
   auto *FrameVoidPtr =
       new BitCastInst(Frame, Type::getInt8PtrTy(C), "vFrame", InsertPt);
 
-  // Replacing llvm.coro.alloc with non-null value will suppress dynamic
-  // allocation as it is expected for the frontend to generate the code that
-  // looks like:
-  //   mem = coro.alloc();
-  //   if (!mem) mem = malloc(coro.size());
-  //   coro.begin(mem, ...)
-  AllocInst->replaceAllUsesWith(FrameVoidPtr);
-  AllocInst->eraseFromParent();
-
-  // To suppress deallocation code, we replace all llvm.coro.free intrinsics
-  // associated with this coro.begin with null constant.
-  auto *NullPtr = ConstantPointerNull::get(Type::getInt8PtrTy(C));
-  coro::replaceAllCoroFrees(CoroBegin, NullPtr);
-  CoroBegin->lowerTo(FrameVoidPtr);
+  for (auto *CB : CoroBegins) {
+    CB->replaceAllUsesWith(FrameVoidPtr);
+    CB->eraseFromParent();
+  }
 
   // Since now coroutine frame lives on the stack we need to make sure that
   // any tail call referencing it, must be made non-tail call.
   removeTailCallAttribute(Frame, AA);
 }
 
-// See if there are any coro.subfn.addr intrinsics directly referencing
-// the coro.begin. If found, replace them with an appropriate coroutine
-// subfunction associated with that coro.begin.
-static bool replaceIndirectCalls(CoroBeginInst *CoroBegin, AAResults &AA) {
-  SmallVector<CoroSubFnInst *, 8> ResumeAddr;
-  SmallVector<CoroSubFnInst *, 8> DestroyAddr;
-
-  for (User *CF : CoroBegin->users()) {
-    assert(isa<CoroFrameInst>(CF) &&
-           "CoroBegin can be only used by coro.frame instructions");
-    for (User *U : CF->users()) {
-      if (auto *II = dyn_cast<CoroSubFnInst>(U)) {
+bool Lowerer::processCoroId(CoroIdInst *CoroId, AAResults &AA) {
+  CoroBegins.clear();
+  CoroAllocs.clear();
+  ResumeAddr.clear();
+  DestroyAddr.clear();
+
+  // Collect all coro.begin and coro.allocs associated with this coro.id.
+  for (User *U : CoroId->users()) {
+    if (auto *CB = dyn_cast<CoroBeginInst>(U))
+      CoroBegins.push_back(CB);
+    else if (auto *CA = dyn_cast<CoroAllocInst>(U))
+      CoroAllocs.push_back(CA);
+  }
+
+  // Collect all coro.subfn.addrs associated with coro.begin.
+  for (CoroBeginInst *CB : CoroBegins) {
+    for (User *U : CB->users())
+      if (auto *II = dyn_cast<CoroSubFnInst>(U))
         switch (II->getIndex()) {
         case CoroSubFnInst::ResumeIndex:
           ResumeAddr.push_back(II);
           break;
         case CoroSubFnInst::DestroyIndex:
           DestroyAddr.push_back(II);
           break;
         default:
           llvm_unreachable("unexpected coro.subfn.addr constant");
         }
-      }
-    }
-  }
-  if (ResumeAddr.empty() && DestroyAddr.empty())
-    return false;
 
-  // PostSplit coro.begin refers to an array of subfunctions in its Info
+  // PostSplit coro.id refers to an array of subfunctions in its Info
   // argument.
-  ConstantArray *Resumers = CoroBegin->getInfo().Resumers;
-  assert(Resumers && "PostSplit coro.begin Info argument must refer to an array"
+  ConstantArray *Resumers = CoroId->getInfo().Resumers;
+  assert(Resumers && "PostSplit coro.id Info argument must refer to an array"
                      "of coroutine subfunctions");
   auto *ResumeAddrConstant =
       ConstantExpr::getExtractValue(Resumers, CoroSubFnInst::ResumeIndex);
+
   replaceWithConstant(ResumeAddrConstant, ResumeAddr);
 
   if (DestroyAddr.empty())
     return true;
 
   auto *DestroyAddrConstant =
       ConstantExpr::getExtractValue(Resumers, CoroSubFnInst::DestroyIndex);
+
   replaceWithConstant(DestroyAddrConstant, DestroyAddr);
 
-  // If llvm.coro.begin refers to llvm.coro.alloc, we can elide the allocation.
-  if (auto *AllocInst = CoroBegin->getAlloc()) {
+  // If there is a coro.alloc that llvm.coro.id refers to, we have the ability
+  // to suppress dynamic allocation.
+  if (!CoroAllocs.empty()) {
     // FIXME: The check above is overly lax. It only checks for whether we have
     // an ability to elide heap allocations, not whether it is safe to do so.
     // We need to do something like:
     // If for every exit from the function where coro.begin is
     // live, there is a coro.free or coro.destroy dominating that exit block,
     // then it is safe to elide heap allocation, since the lifetime of coroutine
     // is fully enclosed in its caller.
     auto *FrameTy = getFrameType(cast<Function>(ResumeAddrConstant));
-    elideHeapAllocations(CoroBegin, FrameTy, AllocInst, AA);
+    elideHeapAllocations(CoroId->getFunction(), FrameTy, AA);
   }
-
   return true;
 }
 
 // See if there are any coro.subfn.addr instructions referring to coro.devirt
 // trigger, if so, replace them with a direct call to devirt trigger function.
 static bool replaceDevirtTrigger(Function &F) {
   SmallVector<CoroSubFnInst *, 1> DevirtAddr;
   for (auto &I : instructions(F))
     if (auto *SubFn = dyn_cast<CoroSubFnInst>(&I))
       if (SubFn->getIndex() == CoroSubFnInst::RestartTrigger)
         DevirtAddr.push_back(SubFn);
 
   if (DevirtAddr.empty())
     return false;
 
   Module &M = *F.getParent();
   Function *DevirtFn = M.getFunction(CORO_DEVIRT_TRIGGER_FN);
   assert(DevirtFn && "coro.devirt.fn not found");
   replaceWithConstant(DevirtFn, DevirtAddr);
 
   return true;
 }
 
-bool CoroElide::runOnFunction(Function &F) {
+//===----------------------------------------------------------------------===//
+//                              Top Level Driver
+//===----------------------------------------------------------------------===//
+
+namespace {
+struct CoroElide : FunctionPass {
+  static char ID;
+  CoroElide() : FunctionPass(ID) {}
+
+  std::unique_ptr<Lowerer> L;
+
+  bool doInitialization(Module &M) override {
+    if (coro::declaresIntrinsics(M, {"llvm.coro.id"}))
+      L = llvm::make_unique<Lowerer>(M);
+    return false;
+  }
+
+  bool runOnFunction(Function &F) override {
+    if (!L)
+      return false;
+
     bool Changed = false;
 
     if (F.hasFnAttribute(CORO_PRESPLIT_ATTR))
       Changed = replaceDevirtTrigger(F);
 
-  // Collect all PostSplit coro.begins.
-  SmallVector<CoroBeginInst *, 4> CoroBegins;
+    L->CoroIds.clear();
+    L->CoroFrees.clear();
+
+    // Collect all PostSplit coro.ids and all coro.free.
     for (auto &I : instructions(F))
-    if (auto *CB = dyn_cast<CoroBeginInst>(&I))
-      if (CB->getInfo().isPostSplit())
-        CoroBegins.push_back(CB);
+      if (auto *CF = dyn_cast<CoroFreeInst>(&I))
+        L->CoroFrees.push_back(CF);
+      else if (auto *CII = dyn_cast<CoroIdInst>(&I))
+        if (CII->getInfo().isPostSplit())
+          L->CoroIds.push_back(CII);
 
-  if (CoroBegins.empty())
+    // If we did not find any coro.id, there is nothing to do.
+    if (L->CoroIds.empty())
       return Changed;
 
     AAResults &AA = getAnalysis<AAResultsWrapperPass>().getAAResults();
-  for (auto *CB : CoroBegins)
-    Changed |= replaceIndirectCalls(CB, AA);
+    for (auto *CII : L->CoroIds)
+      Changed |= L->processCoroId(CII, AA);
 
     return Changed;
   }
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.addRequired<AAResultsWrapperPass>();
+    AU.setPreservesCFG();
+  }
+};
+}
+
+char CoroElide::ID = 0;
+INITIALIZE_PASS_BEGIN(
+    CoroElide, "coro-elide",
+    "Coroutine frame allocation elision and indirect calls replacement", false,
+    false)
+INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
+INITIALIZE_PASS_END(
+    CoroElide, "coro-elide",
+    "Coroutine frame allocation elision and indirect calls replacement", false,
+    false)
+
+Pass *llvm::createCoroElidePass() { return new CoroElide(); }

lib/Transforms/Coroutines/CoroInstr.h

 //===-- CoroInstr.h - Coroutine Intrinsics Instruction Wrappers -*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 // This file defines classes that make it really easy to deal with intrinsic
 // functions with the isa/dyncast family of functions.  In particular, this
 // allows you to do things like:
 //
 //     if (auto *SF = dyn_cast<CoroSubFnInst>(Inst))
-//        ... SF->getFrame() ... SF->getAlloc() ...
+//        ... SF->getFrame() ... 
 //
 // All intrinsic function calls are instances of the call instruction, so these
 // are all subclasses of the CallInst class.  Note that none of these classes
 // has state or virtual methods, which is an important part of this gross/neat
 // hack working.
 //
 // The helpful comment above is borrowed from llvm/IntrinsicInst.h, we keep
 // coroutine intrinsic wrappers here since they are only used by the passes in
public:
   static inline bool classof(const IntrinsicInst *I) {
     return I->getIntrinsicID() == Intrinsic::coro_alloc;
   }
   static inline bool classof(const Value *V) {
     return isa<IntrinsicInst>(V) && classof(cast<IntrinsicInst>(V));
   }
 };
 
-/// This represents the llvm.coro.frame instruction.
-class LLVM_LIBRARY_VISIBILITY CoroFrameInst : public IntrinsicInst {
-public:
-  // Methods to support type inquiry through isa, cast, and dyn_cast:
-  static inline bool classof(const IntrinsicInst *I) {
-    return I->getIntrinsicID() == Intrinsic::coro_frame;
-  }
-  static inline bool classof(const Value *V) {
-    return isa<IntrinsicInst>(V) && classof(cast<IntrinsicInst>(V));
-  }
-};
-
-/// This represents the llvm.coro.free instruction.
-class LLVM_LIBRARY_VISIBILITY CoroFreeInst : public IntrinsicInst {
-public:
-  // Methods to support type inquiry through isa, cast, and dyn_cast:
-  static inline bool classof(const IntrinsicInst *I) {
-    return I->getIntrinsicID() == Intrinsic::coro_free;
-  }
-  static inline bool classof(const Value *V) {
-    return isa<IntrinsicInst>(V) && classof(cast<IntrinsicInst>(V));
-  }
-};
-
-/// This class represents the llvm.coro.begin instruction.
-class LLVM_LIBRARY_VISIBILITY CoroBeginInst : public IntrinsicInst {
-  enum { MemArg, ElideArg, AlignArg, PromiseArg, InfoArg };
-
+/// This represents the llvm.coro.alloc instruction.
+class LLVM_LIBRARY_VISIBILITY CoroIdInst : public IntrinsicInst {
+  enum { AlignArg, PromiseArg, InfoArg };
 public:
-  CoroAllocInst *getAlloc() const {
-    if (auto *CAI = dyn_cast<CoroAllocInst>(
-            getArgOperand(ElideArg)->stripPointerCasts()))
-      return CAI;
-
-    return nullptr;
-  }
-
-  Value *getMem() const { return getArgOperand(MemArg); }
-
-  Constant *getRawInfo() const {
-    return cast<Constant>(getArgOperand(InfoArg)->stripPointerCasts());
-  }
-
-  void setInfo(Constant *C) { setArgOperand(InfoArg, C); }
-
-  // Info argument of coro.begin is
+  // Info argument of coro.id is
   //   fresh out of the frontend: null ;
   //   outlined                 : {Init, Return, Susp1, Susp2, ...} ;
   //   postsplit                : [resume, destroy, cleanup] ;
   //
   // If parts of the coroutine were outlined to protect against undesirable
   // code motion, these functions will be stored in a struct literal referred to
   // by the Info parameter. Note: this is only needed before coroutine is split.
   //
Info getInfo() const {
     assert(GV->isConstant() && GV->hasDefinitiveInitializer());
     Constant *Initializer = GV->getInitializer();
     if ((Result.OutlinedParts = dyn_cast<ConstantStruct>(Initializer)))
       return Result;
 
     Result.Resumers = cast<ConstantArray>(Initializer);
     return Result;
   }
+  Constant *getRawInfo() const {
+    return cast<Constant>(getArgOperand(InfoArg)->stripPointerCasts());
+  }
+
+  void setInfo(Constant *C) { setArgOperand(InfoArg, C); }
+
+
+  // Methods to support type inquiry through isa, cast, and dyn_cast:
+  static inline bool classof(const IntrinsicInst *I) {
+    return I->getIntrinsicID() == Intrinsic::coro_id;
+  }
+  static inline bool classof(const Value *V) {
+    return isa<IntrinsicInst>(V) && classof(cast<IntrinsicInst>(V));
+  }
+};
+
+/// This represents the llvm.coro.frame instruction.
+class LLVM_LIBRARY_VISIBILITY CoroFrameInst : public IntrinsicInst {
+public:
+  // Methods to support type inquiry through isa, cast, and dyn_cast:
+  static inline bool classof(const IntrinsicInst *I) {
+    return I->getIntrinsicID() == Intrinsic::coro_frame;
+  }
+  static inline bool classof(const Value *V) {
+    return isa<IntrinsicInst>(V) && classof(cast<IntrinsicInst>(V));
+  }
+};
 
-  // Replaces all coro.frame intrinsics that are associated with this coro.begin
-  // to a replacement value and removes coro.begin and all of the coro.frame
-  // intrinsics.
-  void lowerTo(Value* Replacement) {
-    SmallVector<CoroFrameInst*, 4> FrameInsts;
-    for (auto *CF : this->users())
-      FrameInsts.push_back(cast<CoroFrameInst>(CF));
-
-    for (auto *CF : FrameInsts) {
-      CF->replaceAllUsesWith(Replacement);
-      CF->eraseFromParent();
-    }
+/// This represents the llvm.coro.free instruction.
+class LLVM_LIBRARY_VISIBILITY CoroFreeInst : public IntrinsicInst {
+public:
+  // Methods to support type inquiry through isa, cast, and dyn_cast:
+  static inline bool classof(const IntrinsicInst *I) {
+    return I->getIntrinsicID() == Intrinsic::coro_free;
+  static inline bool classof(const Value *V) {
+    return isa<IntrinsicInst>(V) && classof(cast<IntrinsicInst>(V));
+  }
+};
+
+/// This class represents the llvm.coro.begin instruction.
+class LLVM_LIBRARY_VISIBILITY CoroBeginInst : public IntrinsicInst {
+  enum { IdArg, MemArg };
 
-    this->eraseFromParent();
+public:
+  CoroIdInst *getId() const {
+    return cast<CoroIdInst>(getArgOperand(IdArg));
   }
 
+  Value *getMem() const { return getArgOperand(MemArg); }
+
   // Methods for support type inquiry through isa, cast, and dyn_cast:
   static inline bool classof(const IntrinsicInst *I) {
     return I->getIntrinsicID() == Intrinsic::coro_begin;
   }
   static inline bool classof(const Value *V) {
     return isa<IntrinsicInst>(V) && classof(cast<IntrinsicInst>(V));
   }
 };
 
 } // End namespace llvm.

lib/Transforms/Coroutines/CoroInternal.h

 #define UNPREPARED_FOR_SPLIT "0"
 #define PREPARED_FOR_SPLIT "1"
 
 #define CORO_DEVIRT_TRIGGER_FN "coro.devirt.trigger"
 
 namespace coro {
 
 bool declaresIntrinsics(Module &M, std::initializer_list<StringRef>);
+void replaceAllCoroAllocs(CoroBeginInst *CB, bool Replacement);
 void replaceAllCoroFrees(CoroBeginInst *CB, Value *Replacement);
 
 // Keeps data and helper functions for lowering coroutine intrinsics.
 struct LowererBase {
   Module &TheModule;
   LLVMContext &Context;
   FunctionType *const ResumeFnType;
 
   LowererBase(Module &M);
   Value *makeSubFnCall(Value *Arg, int Index, Instruction *InsertPt);
 };
 
 } // End namespace coro.
 } // End namespace llvm
 
 #endif

lib/Transforms/Coroutines/Coroutines.cpp

auto *Bitcast =
       new BitCastInst(Call, ResumeFnType->getPointerTo(), "", InsertPt);
   return Bitcast;
 }
 
 #ifndef NDEBUG
 static bool isCoroutineIntrinsicName(StringRef Name) {
   // NOTE: Must be sorted!
   static const char *const CoroIntrinsics[] = {
-      "llvm.coro.alloc",   "llvm.coro.begin", "llvm.coro.destroy",
-      "llvm.coro.done",    "llvm.coro.end",   "llvm.coro.frame",
-      "llvm.coro.free",    "llvm.coro.param", "llvm.coro.promise",
-      "llvm.coro.resume",  "llvm.coro.save",  "llvm.coro.size",
-      "llvm.coro.suspend",
+      "llvm.coro.alloc",   "llvm.coro.begin",   "llvm.coro.destroy",
+      "llvm.coro.done",    "llvm.coro.end",     "llvm.coro.frame",
+      "llvm.coro.free",    "llvm.coro.id",      "llvm.coro.param",
+      "llvm.coro.promise", "llvm.coro.resume",  "llvm.coro.save",
+      "llvm.coro.size",    "llvm.coro.suspend",
   };
   return Intrinsic::lookupLLVMIntrinsicByName(CoroIntrinsics, Name) != -1;
 }
 #endif
 
 // Verifies if a module has named values listed. Also, in debug mode verifies
 // that names are intrinsic names.
 bool coro::declaresIntrinsics(Module &M,
                               std::initializer_list<StringRef> List) {
 
   for (StringRef Name : List) {
     assert(isCoroutineIntrinsicName(Name) && "not a coroutine intrinsic");
     if (M.getNamedValue(Name))
       return true;
   }
 
   return false;
 }
-
-// Find all llvm.coro.free instructions associated with the provided coro.begin
-// and replace them with the provided replacement value.
-void coro::replaceAllCoroFrees(CoroBeginInst *CB, Value *Replacement) {
-  SmallVector<CoroFreeInst *, 4> CoroFrees;
-  for (User *FramePtr: CB->users())
-    for (User *U : FramePtr->users())
-      if (auto *CF = dyn_cast<CoroFreeInst>(U))
-        CoroFrees.push_back(CF);
-
-  if (CoroFrees.empty())
-    return;
-
-  for (CoroFreeInst *CF : CoroFrees) {
-    CF->replaceAllUsesWith(Replacement);
-    CF->eraseFromParent();
-  }
-}

test/Transforms/Coroutines/coro-elide.ll

 }
 
 @f.resumers = internal constant [2 x void (i8*)*] [void (i8*)* @f.resume,
                                                    void (i8*)* @f.destroy]
 
 ; a coroutine start function
 define i8* @f() {
 entry:
-  %tok = call token @llvm.coro.begin(i8* null, i8* null, i32 0, i8* null,
+  %id = call token @llvm.coro.id(i32 0, i8* null,
                           i8* bitcast ([2 x void (i8*)*]* @f.resumers to i8*))
-  %hdl = call i8* @llvm.coro.frame(token %tok)
+  %hdl = call i8* @llvm.coro.begin(token %id, i8* null)
   ret i8* %hdl
 }
 
 ; CHECK-LABEL: @callResume(
 define void @callResume() {
 entry:
-; CHECK: call token @llvm.coro.begin
+; CHECK: call i8* @llvm.coro.begin
   %hdl = call i8* @f()
 
 ; CHECK-NEXT: call void @print(i32 0)
   %0 = call i8* @llvm.coro.subfn.addr(i8* %hdl, i8 0)
   %1 = bitcast i8* %0 to void (i8*)*
   call fastcc void %1(i8* %hdl)
 
 ; CHECK-NEXT: call void @print(i32 1)
   %2 = call i8* @llvm.coro.subfn.addr(i8* %hdl, i8 1)
   %3 = bitcast i8* %2 to void (i8*)*
   call fastcc void %3(i8* %hdl)
 
 ; CHECK-NEXT: ret void
   ret void
 }
 
 ; CHECK-LABEL: @eh(
 define void @eh() personality i8* null {
 entry:
-; CHECK: call token @llvm.coro.begin
+; CHECK: call i8* @llvm.coro.begin
   %hdl = call i8* @f()
 
 ; CHECK-NEXT: call void @print(i32 0)
   %0 = call i8* @llvm.coro.subfn.addr(i8* %hdl, i8 0)
   %1 = bitcast i8* %0 to void (i8*)*
   invoke void %1(i8* %hdl)
           to label %cont unwind label %ehcleanup
 cont:
   ret void
 
 ehcleanup:
   %tok = cleanuppad within none []
   cleanupret from %tok unwind to caller
 }
 
 ; CHECK-LABEL: @no_devirt_info_null(
 ; no devirtualization here, since coro.begin info parameter is null
 define void @no_devirt_info_null() {
 entry:
-  %tok = call token @llvm.coro.begin(i8* null, i8* null, i32 0, i8* null, i8* null)
-  %hdl = call i8* @llvm.coro.frame(token %tok)
+  %id = call token @llvm.coro.id(i32 0, i8* null, i8* null)
+  %hdl = call i8* @llvm.coro.begin(token %id, i8* null)
 
 ; CHECK: call i8* @llvm.coro.subfn.addr(i8* %hdl, i8 0)
   %0 = call i8* @llvm.coro.subfn.addr(i8* %hdl, i8 0)
   %1 = bitcast i8* %0 to void (i8*)*
   call fastcc void %1(i8* %hdl)
 
 ; CHECK: call i8* @llvm.coro.subfn.addr(i8* %hdl, i8 1)
   %2 = call i8* @llvm.coro.subfn.addr(i8* %hdl, i8 1)
; CHECK: call i8* @llvm.coro.subfn.addr(i8* %hdl, i8 1)
   %2 = call i8* @llvm.coro.subfn.addr(i8* %hdl, i8 1)
   %3 = bitcast i8* %2 to void (i8*)*
   call fastcc void %3(i8* %hdl)
 
 ; CHECK: ret void
   ret void
 }
 
-
-declare token @llvm.coro.begin(i8*, i8*, i32, i8*, i8*)
-declare i8* @llvm.coro.frame(token)
+declare token @llvm.coro.id(i32, i8*, i8*)
+declare i8* @llvm.coro.begin(token, i8*)
+declare i8* @llvm.coro.frame()
 declare i8* @llvm.coro.subfn.addr(i8*, i8)

test/Transforms/Coroutines/coro-heap-elide.ll

 declare void @CustomFree(i8*)
 
 @f.resumers = internal constant 
   [2 x void (%f.frame*)*] [void (%f.frame*)* @f.resume, void (%f.frame*)* @f.destroy]
 
 ; a coroutine start function
 define i8* @f() personality i8* null {
 entry:
-  %elide = call i8* @llvm.coro.alloc()
-  %need.dyn.alloc = icmp ne i8* %elide, null
-  br i1 %need.dyn.alloc, label %coro.begin, label %dyn.alloc
+  %id = call token @llvm.coro.id(i32 0, i8* null,
+                      i8* bitcast ([2 x void (%f.frame*)*]* @f.resumers to i8*))
+  %need.dyn.alloc = call i1 @llvm.coro.alloc(token %id)
+  br i1 %need.dyn.alloc, label %dyn.alloc, label %coro.begin
 dyn.alloc:
   %alloc = call i8* @CustomAlloc(i32 4)
   br label %coro.begin
 coro.begin:
-  %phi = phi i8* [ %elide, %entry ], [ %alloc, %dyn.alloc ]
-  %beg = call token @llvm.coro.begin(i8* %phi, i8* %elide, i32 0, i8* null,
-                          i8* bitcast ([2 x void (%f.frame*)*]* @f.resumers to i8*))
-  %hdl = call i8* @llvm.coro.frame(token %beg)
+  %phi = phi i8* [ null, %entry ], [ %alloc, %dyn.alloc ]
+  %hdl = call i8* @llvm.coro.begin(token %id, i8* %phi)
   invoke void @may_throw() 
     to label %ret unwind label %ehcleanup
 ret:          
   ret i8* %hdl
 
 ehcleanup:
   %tok = cleanuppad within none []
   %mem = call i8* @llvm.coro.free(i8* %hdl)

 ; CHECK-NEXT: ret void
   ret void
 }
 
 ; a coroutine start function (cannot elide heap alloc, due to second argument to
 ; coro.begin not pointint to coro.alloc)
 define i8* @f_no_elision() personality i8* null {
 entry:
-  %alloc = call i8* @CustomAlloc(i32 4)
-  %beg = call token @llvm.coro.begin(i8* %alloc, i8* null, i32 0, i8* null,
-                          i8* bitcast ([2 x void (%f.frame*)*]* @f.resumers to i8*))
-  %hdl = call i8* @llvm.coro.frame(token %beg)
+  %id = call token @llvm.coro.id(i32 0, i8* null,
+  %alloc = call i8* @CustomAlloc(i32 4)
+  %hdl = call i8* @llvm.coro.begin(token %id, i8* %alloc)
   ret i8* %hdl
 }
 
 ; CHECK-LABEL: @callResume_no_elision(
 define void @callResume_no_elision() {
 entry:
 ; CHECK: call i8* @CustomAlloc(
   %hdl = call i8* @f_no_elision()
; CHECK-NEXT: call fastcc void bitcast (void (%f.frame*)* @f.destroy to void (i8*)*)(i8*
   %2 = call i8* @llvm.coro.subfn.addr(i8* %hdl, i8 1)
   %3 = bitcast i8* %2 to void (i8*)*
   call fastcc void %3(i8* %hdl)
 
 ; CHECK-NEXT: ret void
   ret void
 }
 
-
-declare i8* @llvm.coro.alloc()
+declare token @llvm.coro.id(i32, i8*, i8*)
+declare i1 @llvm.coro.alloc(token)
 declare i8* @llvm.coro.free(i8*)
-declare token @llvm.coro.begin(i8*, i8*, i32, i8*, i8*)
+declare i8* @llvm.coro.begin(token, i8*)
 declare i8* @llvm.coro.frame(token)
 declare i8* @llvm.coro.subfn.addr(i8*, i8)

test/Transforms/Coroutines/restart-trigger.ll

 ; Verifies that restart trigger forces IPO pipelines restart and the same
 ; coroutine is looked at by CoroSplit pass twice.
 ; REQUIRES: asserts
 ; RUN: opt < %s -S -O0 -enable-coroutines -debug-only=coro-split 2>&1 | FileCheck %s
 ; RUN: opt < %s -S -O1 -enable-coroutines -debug-only=coro-split 2>&1 | FileCheck %s
 
 ; CHECK:      CoroSplit: Processing coroutine 'f' state: 0
 ; CHECK-NEXT: CoroSplit: Processing coroutine 'f' state: 1
 
-declare token @llvm.coro.begin(i8*, i8*, i32, i8*, i8*)
+declare token @llvm.coro.id(i32, i8*, i8*)
+declare i8* @llvm.coro.begin(token, i8*)
 
 ; a coroutine start function
 define void @f() {
-  call token @llvm.coro.begin(i8* null, i8* null, i32 0, i8* null, i8* null)
+  %id = call token @llvm.coro.id(i32 0, i8* null, i8* null)
+  call i8* @llvm.coro.begin(token %id, i8* null)
   ret void
 }