[clang] [OpenMP][OMPIRBuilder] Add support to omp target parallel (PR #67000)

[Johannes Doerfert via cfe-commits]

================
@@ -1126,6 +1133,185 @@ void OpenMPIRBuilder::emitCancelationCheckImpl(Value *CancelFlag,
   Builder.SetInsertPoint(NonCancellationBlock, NonCancellationBlock->begin());
 }
 
+// Callback used to create OpenMP runtime calls to support
+// omp parallel clause for the device.
+// We need to use this callback to replace call to the OutlinedFn in OuterFn
+// by the call to the OpenMP DeviceRTL runtime function (kmpc_parallel_51)
+static void
+targetParallelCallback(OpenMPIRBuilder *OMPIRBuilder, Function &OutlinedFn,
+                       Function *OuterFn, Value *Ident, Value *IfCondition,
+                       Value *NumThreads, Instruction *PrivTID,
+                       AllocaInst *PrivTIDAddr, Value *ThreadID,
+                       const SmallVector<Instruction *, 4> &ToBeDeleted) {
+  // Add some known attributes.
+  Module &M = OMPIRBuilder->M;
+  IRBuilder<> &Builder = OMPIRBuilder->Builder;
+  OutlinedFn.addParamAttr(0, Attribute::NoAlias);
+  OutlinedFn.addParamAttr(1, Attribute::NoAlias);
+  OutlinedFn.addParamAttr(0, Attribute::NoUndef);
+  OutlinedFn.addParamAttr(1, Attribute::NoUndef);
+  OutlinedFn.addFnAttr(Attribute::NoUnwind);
+
+  assert(OutlinedFn.arg_size() >= 2 &&
+         "Expected at least tid and bounded tid as arguments");
+  unsigned NumCapturedVars = OutlinedFn.arg_size() - /* tid & bounded tid */ 2;
+
+  CallInst *CI = cast<CallInst>(OutlinedFn.user_back());
+  assert(CI && "Expected call instruction to outlined function");
+  CI->getParent()->setName("omp_parallel");
+  // Replace direct call to the outlined function by the call to
+  // __kmpc_parallel_51
+  Builder.SetInsertPoint(CI);
+
+  // Build call __kmpc_parallel_51
+  auto PtrTy = Type::getInt8PtrTy(M.getContext());
+  Value *Void = ConstantPointerNull::get(PtrTy);
+  // Add alloca for kernel args. Put this instruction at the beginning
+  // of the function.
+  OpenMPIRBuilder ::InsertPointTy CurrentIP = Builder.saveIP();
+  Builder.SetInsertPoint(&OuterFn->front(),
+                         OuterFn->front().getFirstInsertionPt());
+  AllocaInst *ArgsAlloca =
+      Builder.CreateAlloca(ArrayType::get(PtrTy, NumCapturedVars));
+  Value *Args =
+      Builder.CreatePointerCast(ArgsAlloca, Type::getInt8PtrTy(M.getContext()));
+  Builder.restoreIP(CurrentIP);
+  // Store captured vars which are used by kmpc_parallel_51
+  if (NumCapturedVars) {
+    for (unsigned Idx = 0; Idx < NumCapturedVars; Idx++) {
+      Value *V = *(CI->arg_begin() + 2 + Idx);
+      Value *StoreAddress = Builder.CreateConstInBoundsGEP2_64(
+          ArrayType::get(PtrTy, NumCapturedVars), Args, 0, Idx);
+      Builder.CreateStore(V, StoreAddress);
+    }
+  }
+  Value *Cond = IfCondition ? Builder.CreateSExtOrTrunc(
+                                  IfCondition, Type::getInt32Ty(M.getContext()))
+                            : Builder.getInt32(1);
+  Value *Parallel51CallArgs[] = {
+      /* identifier*/ Ident,
+      /* global thread num*/ ThreadID,
+      /* if expression */ Cond, NumThreads ? NumThreads : Builder.getInt32(-1),
----------------
jdoerfert wrote:

Either provide comments for all arguments or none. this is confusing.

https://github.com/llvm/llvm-project/pull/67000