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

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-mlir

Author: Pranav Bhandarkar (bhandarkar-pranav)

<details>
<summary>Changes</summary>

This patch fixes 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 https://github.com/llvm/llvm-project/issues/90869

---
Full diff: https://github.com/llvm/llvm-project/pull/90891.diff


2 Files Affected:

- (modified) llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp (+9) 
- (added) mlir/test/Target/LLVMIR/omptask_if_false.mlir (+23) 


``````````diff
diff --git a/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp b/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp
index 4d2d352f7520b2..695308419e0d20 100644
--- a/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp
+++ b/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp
@@ -1887,6 +1887,15 @@ OpenMPIRBuilder::createTask(const LocationDescription &Loc,
       SplitBlockAndInsertIfThenElse(IfCondition, IfTerminator, &ThenTI,
                                     &ElseTI);
       Builder.SetInsertPoint(ElseTI);
+
+      if (Dependencies.size()) {
+        Function *TaskWaitFn =
+            getOrCreateRuntimeFunctionPtr(OMPRTL___kmpc_omp_taskwait_deps_51);
+        Builder.CreateCall(TaskWaitFn, {Ident, ThreadID, Builder.getInt32(Dependencies.size()),
+                                        DepArray, ConstantInt::get(Builder.getInt32Ty(), 0),
+                                        ConstantPointerNull::get(PointerType::getUnqual(M.getContext())),
+                                        ConstantInt::get(Builder.getInt32Ty(), false)});
+      }
       Function *TaskBeginFn =
           getOrCreateRuntimeFunctionPtr(OMPRTL___kmpc_omp_task_begin_if0);
       Function *TaskCompleteFn =
diff --git a/mlir/test/Target/LLVMIR/omptask_if_false.mlir b/mlir/test/Target/LLVMIR/omptask_if_false.mlir
new file mode 100644
index 00000000000000..c7fd5eb62a9772
--- /dev/null
+++ b/mlir/test/Target/LLVMIR/omptask_if_false.mlir
@@ -0,0 +1,23 @@
+// RUN: mlir-translate -mlir-to-llvmir %s | FileCheck %s
+
+module attributes {dlti.dl_spec = #dlti.dl_spec<#dlti.dl_entry<!llvm.ptr<270>, dense<32> : vector<4xi64>>, #dlti.dl_entry<i64, dense<64> : vector<2xi64>>, #dlti.dl_entry<i32, dense<32> : vector<2xi64>>, #dlti.dl_entry<!llvm.ptr<272>, dense<64> : vector<4xi64>>, #dlti.dl_entry<!llvm.ptr<271>, dense<32> : vector<4xi64>>, #dlti.dl_entry<f16, dense<16> : vector<2xi64>>, #dlti.dl_entry<f64, dense<64> : vector<2xi64>>, #dlti.dl_entry<f128, dense<128> : vector<2xi64>>, #dlti.dl_entry<f80, dense<128> : vector<2xi64>>, #dlti.dl_entry<i128, dense<128> : vector<2xi64>>, #dlti.dl_entry<i16, dense<16> : vector<2xi64>>, #dlti.dl_entry<i8, dense<8> : vector<2xi64>>, #dlti.dl_entry<i1, dense<8> : vector<2xi64>>, #dlti.dl_entry<!llvm.ptr, dense<64> : vector<4xi64>>, #dlti.dl_entry<"dlti.endianness", "little">, #dlti.dl_entry<"dlti.stack_alignment", 128 : i64>>, fir.defaultkind = "a1c4d8i4l4r4", fir.kindmap = "", llvm.data_layout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128", llvm.target_triple = "x86_64-unknown-linux-gnu", omp.is_gpu = false, omp.is_target_device = false, omp.version = #omp.version<version = 11>}
+{
+  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
+  }
+  llvm.func @llvm.stacksave.p0() -> !llvm.ptr attributes {sym_visibility = "private"}
+  llvm.func @llvm.stackrestore.p0(!llvm.ptr) attributes {sym_visibility = "private"}
+}
+
+
+// CHECK: call void @__kmpc_omp_taskwait_deps_51
+// 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
+

``````````

</details>


https://github.com/llvm/llvm-project/pull/90891