[OMPIRBuilder] - Handle dependencies in createTarget (#93977)

Summary:
This patch handles dependencies specified by the `depend` clause on an
OpenMP target construct. It does this much the same way clang does it by
materializing an OpenMP `task` that is tagged with the dependencies.

The following functions are relevant to this patch -
1) `createTarget` - This function itself is largely unchanged except
that it now accepts a vector of `DependData` objects that it simply
forwards to `emitTargetCall`
2) `emitTargetCall` - This function has changed now to check if an outer
target-task needs to be materialized (i.e if `target` construct has
`nowait` or has `depend` clause). If yes, it calls `emitTargetTask` to
do all the heavy lifting for creating and dispatching the task.
3) `emitTargetTask` - Bulk of the change is here. See the large comment
explaining what it does at the beginning of this function

Test Plan: 

Reviewers: 

Subscribers: 

Tasks: 

Tags: 


Differential Revision: https://phabricator.intern.facebook.com/D60251117

Author: bhandarkar-pranav

llvm/include/llvm/Frontend/OpenMP/OMPIRBuilder.h

@@ -2322,6 +2322,26 @@ class OpenMPIRBuilder {
       EmitFallbackCallbackTy EmitTargetCallFallbackCB, TargetKernelArgs &Args,
       Value *DeviceID, Value *RTLoc, InsertPointTy AllocaIP);
 
+  /// Generate a target-task for the target construct
+  ///
+  /// \param OutlinedFn The outlined device/target kernel function.
+  /// \param OutlinedFnID The ooulined function ID.
+  /// \param EmitTargetCallFallbackCB Call back function to generate host
+  ///        fallback code.
+  /// \param Args Data structure holding information about the kernel arguments.
+  /// \param DeviceID Identifier for the device via the 'device' clause.
+  /// \param RTLoc Source location identifier
+  /// \param AllocaIP The insertion point to be used for alloca instructions.
+  /// \param Dependencies Vector of DependData objects holding information of
+  ///        dependencies as specified by the 'depend' clause.
+  /// \param HasNoWait True if the target construct had 'nowait' on it, false
+  ///        otherwise
+  InsertPointTy emitTargetTask(
+      Function *OutlinedFn, Value *OutlinedFnID,
+      EmitFallbackCallbackTy EmitTargetCallFallbackCB, TargetKernelArgs &Args,
+      Value *DeviceID, Value *RTLoc, InsertPointTy AllocaIP,
+      SmallVector<OpenMPIRBuilder::DependData> &Dependencies, bool HasNoWait);
+
   /// Emit the arguments to be passed to the runtime library based on the
   /// arrays of base pointers, pointers, sizes, map types, and mappers.  If
   /// ForEndCall, emit map types to be passed for the end of the region instead
@@ -2805,6 +2825,8 @@ class OpenMPIRBuilder {
   /// \param BodyGenCB Callback that will generate the region code.
   /// \param ArgAccessorFuncCB Callback that will generate accessors
   /// instructions for passed in target arguments where neccessary
+  /// \param Dependencies A vector of DependData objects that carry
+  // dependency information as passed in the depend clause
   InsertPointTy createTarget(const LocationDescription &Loc,
                              OpenMPIRBuilder::InsertPointTy AllocaIP,
                              OpenMPIRBuilder::InsertPointTy CodeGenIP,
@@ -2813,7 +2835,8 @@ class OpenMPIRBuilder {
                              SmallVectorImpl<Value *> &Inputs,
                              GenMapInfoCallbackTy GenMapInfoCB,
                              TargetBodyGenCallbackTy BodyGenCB,
-                             TargetGenArgAccessorsCallbackTy ArgAccessorFuncCB);
+                             TargetGenArgAccessorsCallbackTy ArgAccessorFuncCB,
+                             SmallVector<DependData> Dependencies = {});
 
   /// Returns __kmpc_for_static_init_* runtime function for the specified
   /// size \a IVSize and sign \a IVSigned. Will create a distribute call