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[coroutines] Add support for allocation elision 

Summary:
We wrap allocation code so that backend can elide it if necessary.
llvm.coro.alloc intrinsic returns true, when allocation is needed and false otherwise.

```
  %NeedAlloc = call i1 @llvm.coro.alloc(token %2)
  br i1 %NeedAlloc, label %AllocBB, label %InitBB

AllocBB:
  %5 = call i64 @llvm.coro.size.i64()
  %call = call i8* @_Znwm(i64 %5) ; operator new
  br label %InitBB

InitBB:
  %Phi = phi i8* [ null, %0 ], [ %call, %4 ]
  call i8* @llvm.coro.begin(token %2, i8* %Phi)
```

Reviewers: majnemer, EricWF

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D31584

llvm-svn: 303596
This commit is contained in:
Gor Nishanov 2017-05-23 01:13:17 +00:00
parent fb9476ee6c
commit aa6e9a99b4
2 changed files with 34 additions and 4 deletions
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27
clang/lib/CodeGen/CGCoroutine.cpp
View File

@ -284,6 +284,9 @@ void CodeGenFunction::EmitCoroutineBody(const CoroutineBodyStmt &S) {
auto &TI = CGM.getContext().getTargetInfo();
unsigned NewAlign = TI.getNewAlign() / TI.getCharWidth();
auto *EntryBB = Builder.GetInsertBlock();
auto *AllocBB = createBasicBlock("coro.alloc");
auto *InitBB = createBasicBlock("coro.init");
auto *FinalBB = createBasicBlock("coro.final");
auto *RetBB = createBasicBlock("coro.ret");
@ -293,12 +296,20 @@ void CodeGenFunction::EmitCoroutineBody(const CoroutineBodyStmt &S) {
createCoroData(*this, CurCoro, CoroId);
CurCoro.Data->SuspendBB = RetBB;
// Backend is allowed to elide memory allocations, to help it, emit
// auto mem = coro.alloc() ? 0 : ... allocation code ...;
auto *CoroAlloc = Builder.CreateCall(
CGM.getIntrinsic(llvm::Intrinsic::coro_alloc), {CoroId});
Builder.CreateCondBr(CoroAlloc, AllocBB, InitBB);
EmitBlock(AllocBB);
auto *AllocateCall = EmitScalarExpr(S.getAllocate());
auto *AllocOrInvokeContBB = Builder.GetInsertBlock();
// Handle allocation failure if 'ReturnStmtOnAllocFailure' was provided.
if (auto *RetOnAllocFailure = S.getReturnStmtOnAllocFailure()) {
auto *RetOnFailureBB = createBasicBlock("coro.ret.on.failure");
auto *InitBB = createBasicBlock("coro.init");
// See if allocation was successful.
auto *NullPtr = llvm::ConstantPointerNull::get(Int8PtrTy);
@ -308,9 +319,19 @@ void CodeGenFunction::EmitCoroutineBody(const CoroutineBodyStmt &S) {
// If not, return OnAllocFailure object.
EmitBlock(RetOnFailureBB);
EmitStmt(RetOnAllocFailure);
EmitBlock(InitBB);
}
else {
Builder.CreateBr(InitBB);
}
EmitBlock(InitBB);
// Pass the result of the allocation to coro.begin.
auto *Phi = Builder.CreatePHI(VoidPtrTy, 2);
Phi->addIncoming(NullPtr, EntryBB);
Phi->addIncoming(AllocateCall, AllocOrInvokeContBB);
Builder.CreateCall(
CGM.getIntrinsic(llvm::Intrinsic::coro_begin), {CoroId, Phi});
CurCoro.Data->CleanupJD = getJumpDestInCurrentScope(RetBB);
{

11
clang/test/CodeGenCoroutines/coro-alloc.cpp
View File

@ -56,8 +56,17 @@ struct std::experimental::coroutine_traits<void, global_new_delete_tag> {
// CHECK-LABEL: f0(
extern "C" void f0(global_new_delete_tag) {
// CHECK: %[[ID:.+]] = call token @llvm.coro.id(i32 16
// CHECK: %[[NeedAlloc:.+]] = call i1 @llvm.coro.alloc(token %[[ID]])
// CHECK: br i1 %[[NeedAlloc]], label %[[AllocBB:.+]], label %[[InitBB:.+]]
// CHECK: [[AllocBB]]:
// CHECK: %[[SIZE:.+]] = call i64 @llvm.coro.size.i64()
// CHECK: call i8* @_Znwm(i64 %[[SIZE]])
// CHECK: %[[MEM:.+]] = call i8* @_Znwm(i64 %[[SIZE]])
// CHECK: br label %[[InitBB]]
// CHECK: [[InitBB]]:
// CHECK: %[[PHI:.+]] = phi i8* [ null, %{{.+}} ], [ %call, %[[AllocBB]] ]
// CHECK: call i8* @llvm.coro.begin(token %[[ID]], i8* %[[PHI]])
// CHECK: %[[FRAME:.+]] = call i8* @llvm.coro.frame()
// CHECK: %[[MEM:.+]] = call i8* @llvm.coro.free(token %[[ID]], i8* %[[FRAME]])