[mlir][OpenMP] - Honor dependencies in code-generation of the if clause in omp.task correctly (llvm#90891)

This patch fixes the code generation of the if clause, specifically when the
condition evaluates to false and when the task directive has the depend
clause on it. When the if clause of a task construct evaluates to false,
then the task is an undeferred task. This undeferred task still has to
honor dependencies. Previously, the OpenMPIRbuilder didn't honor
dependencies. This patch fixes that.

Fixes llvm#90869

Author: bhandarkar-pranav

llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp

@@ -1870,6 +1870,9 @@ OpenMPIRBuilder::createTask(const LocationDescription &Loc,
     //    call @__kmpc_omp_task(...)
     //    br label %exit
     //  else:
+    //    ;; Wait for resolution of dependencies, if any, before
+    //    ;; beginning the task
+    //    call @__kmpc_omp_wait_deps(...)
     //    call @__kmpc_omp_task_begin_if0(...)
     //    call @outlined_fn(...)
     //    call @__kmpc_omp_task_complete_if0(...)
@@ -1887,6 +1890,16 @@ OpenMPIRBuilder::createTask(const LocationDescription &Loc,
       SplitBlockAndInsertIfThenElse(IfCondition, IfTerminator, &ThenTI,
                                     &ElseTI);
       Builder.SetInsertPoint(ElseTI);
+
+      if (Dependencies.size()) {
+        Function *TaskWaitFn =
+            getOrCreateRuntimeFunctionPtr(OMPRTL___kmpc_omp_wait_deps);
+        Builder.CreateCall(
+            TaskWaitFn,
+            {Ident, ThreadID, Builder.getInt32(Dependencies.size()), DepArray,
+             ConstantInt::get(Builder.getInt32Ty(), 0),
+             ConstantPointerNull::get(PointerType::getUnqual(M.getContext()))});
+      }
       Function *TaskBeginFn =
           getOrCreateRuntimeFunctionPtr(OMPRTL___kmpc_omp_task_begin_if0);
       Function *TaskCompleteFn =

mlir/test/Target/LLVMIR/omptask_if_false.mlir

@@ -0,0 +1,17 @@
+// RUN: mlir-translate -mlir-to-llvmir %s | FileCheck %s
+
+llvm.func @foo_(%arg0: !llvm.ptr {fir.bindc_name = "n"}, %arg1: !llvm.ptr {fir.bindc_name = "r"}) attributes {fir.internal_name = "_QPfoo"} {
+  %0 = llvm.mlir.constant(false) : i1
+  omp.task if(%0) depend(taskdependin -> %arg0 : !llvm.ptr) {
+    %1 = llvm.load %arg0 : !llvm.ptr -> i32
+    llvm.store %1, %arg1 : i32, !llvm.ptr
+    omp.terminator
+  }
+  llvm.return
+}
+
+// CHECK: call void @__kmpc_omp_wait_deps
+// CHECK-NEXT: call void @__kmpc_omp_task_begin_if0
+// CHECK-NEXT: call void @foo_..omp_par
+// CHECK-NEXT: call void @__kmpc_omp_task_complete_if0
+