[coroutines] Add support for deallocation elision

Wrap deallocation code with:

  if (auto *mem = coro.free()) Deallocate

When backend decides to elide allocations it will replace coro.free with nullptr to suppress deallocation code.

llvm-svn: 303599
This commit is contained in:
Gor Nishanov 2017-05-23 04:21:27 +00:00
parent 68fe6ee768
commit 6c4530c6b5
2 changed files with 58 additions and 8 deletions

View File

@ -62,6 +62,10 @@ struct clang::CodeGen::CGCoroData {
// the address of the coroutine frame of the current coroutine.
llvm::CallInst *CoroBegin = nullptr;
// Stores the last emitted coro.free for the deallocate expressions, we use it
// to wrap dealloc code with if(auto mem = coro.free) dealloc(mem).
llvm::CallInst *LastCoroFree = nullptr;
// If coro.id came from the builtin, remember the expression to give better
// diagnostic. If CoroIdExpr is nullptr, the coro.id was created by
// EmitCoroutineBody.
@ -262,14 +266,47 @@ namespace {
struct CallCoroDelete final : public EHScopeStack::Cleanup {
Stmt *Deallocate;
// TODO: Wrap deallocate in if(coro.free(...)) Deallocate.
// Emit "if (coro.free(CoroId, CoroBegin)) Deallocate;"
// Note: That deallocation will be emitted twice: once for a normal exit and
// once for exceptional exit. This usage is safe because Deallocate does not
// contain any declarations. The SubStmtBuilder::makeNewAndDeleteExpr()
// builds a single call to a deallocation function which is safe to emit
// multiple times.
void Emit(CodeGenFunction &CGF, Flags) override {
// Note: That deallocation will be emitted twice: once for a normal exit and
// once for exceptional exit. This usage is safe because Deallocate does not
// contain any declarations. The SubStmtBuilder::makeNewAndDeleteExpr()
// builds a single call to a deallocation function which is safe to emit
// multiple times.
// Remember the current point, as we are going to emit deallocation code
// first to get to coro.free instruction that is an argument to a delete
// call.
BasicBlock *SaveInsertBlock = CGF.Builder.GetInsertBlock();
auto *FreeBB = CGF.createBasicBlock("coro.free");
CGF.EmitBlock(FreeBB);
CGF.EmitStmt(Deallocate);
auto *AfterFreeBB = CGF.createBasicBlock("after.coro.free");
CGF.EmitBlock(AfterFreeBB);
// We should have captured coro.free from the emission of deallocate.
auto *CoroFree = CGF.CurCoro.Data->LastCoroFree;
if (!CoroFree) {
CGF.CGM.Error(Deallocate->getLocStart(),
"Deallocation expressoin does not refer to coro.free");
return;
}
// Get back to the block we were originally and move coro.free there.
auto *InsertPt = SaveInsertBlock->getTerminator();
CoroFree->moveBefore(InsertPt);
CGF.Builder.SetInsertPoint(InsertPt);
// Add if (auto *mem = coro.free) Deallocate;
auto *NullPtr = llvm::ConstantPointerNull::get(CGF.Int8PtrTy);
auto *Cond = CGF.Builder.CreateICmpNE(CoroFree, NullPtr);
CGF.Builder.CreateCondBr(Cond, FreeBB, AfterFreeBB);
// No longer need old terminator.
InsertPt->eraseFromParent();
CGF.Builder.SetInsertPoint(AfterFreeBB);
}
explicit CallCoroDelete(Stmt *DeallocStmt) : Deallocate(DeallocStmt) {}
};
@ -431,7 +468,7 @@ RValue CodeGenFunction::EmitCoroutineIntrinsic(const CallExpr *E,
llvm::Value *F = CGM.getIntrinsic(IID);
llvm::CallInst *Call = Builder.CreateCall(F, Args);
// Note: The following code is to enable to emit coroutine intrinsics by
// Note: The following code is to enable to emit coro.id and coro.begin by
// hand to experiment with coroutines in C.
// If we see @llvm.coro.id remember it in the CoroData. We will update
// coro.alloc, coro.begin and coro.free intrinsics to refer to it.
@ -442,5 +479,10 @@ RValue CodeGenFunction::EmitCoroutineIntrinsic(const CallExpr *E,
if (CurCoro.Data)
CurCoro.Data->CoroBegin = Call;
}
return RValue::get(Call);
else if (IID == llvm::Intrinsic::coro_free) {
// Remember the last coro_free as we need it to build the conditional
// deletion of the coroutine frame.
if (CurCoro.Data)
CurCoro.Data->LastCoroFree = Call;
} return RValue::get(Call);
}

View File

@ -69,7 +69,15 @@ extern "C" void f0(global_new_delete_tag) {
// CHECK: %[[FRAME:.+]] = call i8* @llvm.coro.begin(token %[[ID]], i8* %[[PHI]])
// CHECK: %[[MEM:.+]] = call i8* @llvm.coro.free(token %[[ID]], i8* %[[FRAME]])
// CHECK: %[[NeedDealloc:.+]] = icmp ne i8* %[[MEM]], null
// CHECK: br i1 %[[NeedDealloc]], label %[[FreeBB:.+]], label %[[Afterwards:.+]]
// CHECK: [[FreeBB]]:
// CHECK: call void @_ZdlPv(i8* %[[MEM]])
// CHECK: br label %[[Afterwards]]
// CHECK: [[Afterwards]]:
// CHECK: ret void
co_return;
}