[OpenMPIRBuilder] Add support for distribute-parallel-for/do constructs

[skatrak]

This patch adds codegen for kmpc_dist_for_static_init runtime calls, used to support worksharing a single loop across teams and threads. This can be used to implement distribute parallel for/do support.

[llvmbot]

@llvm/pr-subscribers-flang-openmp

Author: Sergio Afonso (skatrak)

Changes

This patch adds codegen for kmpc_dist_for_static_init runtime calls, used to support worksharing a single loop across teams and threads. This can be used to implement distribute parallel for/do support.

---

Full diff: https://github.com/llvm/llvm-project/pull/127818.diff

1 Files Affected:

• (modified) llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp (+30-4)

diff --git a/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp b/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp
index 9e380bf2d3dbe..7788897fc0795 100644
--- a/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp
+++ b/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp
@@ -4130,6 +4130,23 @@ Expected<CanonicalLoopInfo *> OpenMPIRBuilder::createCanonicalLoop(
   return createCanonicalLoop(LoopLoc, BodyGen, TripCount, Name);
 }
 
+// Returns an LLVM function to call for initializing loop bounds using OpenMP
+// static scheduling for composite `distribute parallel for` depending on
+// `type`. Only i32 and i64 are supported by the runtime. Always interpret
+// integers as unsigned similarly to CanonicalLoopInfo.
+static FunctionCallee
+getKmpcDistForStaticInitForType(Type *Ty, Module &M,
+                                OpenMPIRBuilder &OMPBuilder) {
+  unsigned Bitwidth = Ty->getIntegerBitWidth();
+  if (Bitwidth == 32)
+    return OMPBuilder.getOrCreateRuntimeFunction(
+        M, omp::RuntimeFunction::OMPRTL___kmpc_dist_for_static_init_4u);
+  if (Bitwidth == 64)
+    return OMPBuilder.getOrCreateRuntimeFunction(
+        M, omp::RuntimeFunction::OMPRTL___kmpc_dist_for_static_init_8u);
+  llvm_unreachable("unknown OpenMP loop iterator bitwidth");
+}
+
 // Returns an LLVM function to call for initializing loop bounds using OpenMP
 // static scheduling depending on `type`. Only i32 and i64 are supported by the
 // runtime. Always interpret integers as unsigned similarly to
@@ -4164,7 +4181,10 @@ OpenMPIRBuilder::InsertPointOrErrorTy OpenMPIRBuilder::applyStaticWorkshareLoop(
   // Declare useful OpenMP runtime functions.
   Value *IV = CLI->getIndVar();
   Type *IVTy = IV->getType();
-  FunctionCallee StaticInit = getKmpcForStaticInitForType(IVTy, M, *this);
+  FunctionCallee StaticInit =
+      LoopType == WorksharingLoopType::DistributeForStaticLoop
+          ? getKmpcDistForStaticInitForType(IVTy, M, *this)
+          : getKmpcForStaticInitForType(IVTy, M, *this);
   FunctionCallee StaticFini =
       getOrCreateRuntimeFunction(M, omp::OMPRTL___kmpc_for_static_fini);
 
@@ -4200,9 +4220,15 @@ OpenMPIRBuilder::InsertPointOrErrorTy OpenMPIRBuilder::applyStaticWorkshareLoop(
 
   // Call the "init" function and update the trip count of the loop with the
   // value it produced.
-  Builder.CreateCall(StaticInit,
-                     {SrcLoc, ThreadNum, SchedulingType, PLastIter, PLowerBound,
-                      PUpperBound, PStride, One, Zero});
+  SmallVector<Value *, 10> Args(
+      {SrcLoc, ThreadNum, SchedulingType, PLastIter, PLowerBound, PUpperBound});
+  if (LoopType == WorksharingLoopType::DistributeForStaticLoop) {
+    Value *PDistUpperBound =
+        Builder.CreateAlloca(IVTy, nullptr, "p.distupperbound");
+    Args.push_back(PDistUpperBound);
+  }
+  Args.append({PStride, One, Zero});
+  Builder.CreateCall(StaticInit, Args);
   Value *LowerBound = Builder.CreateLoad(IVTy, PLowerBound);
   Value *InclusiveUpperBound = Builder.CreateLoad(IVTy, PUpperBound);
   Value *TripCountMinusOne = Builder.CreateSub(InclusiveUpperBound, LowerBound);

[skatrak]

PR stack:

• [MLIR][OpenMP] Prevent loop wrapper translation crashes #115475
• [MLIR][OpenMP] Normalize lowering of omp.loop_nest #127217
• [OpenMPIRBuilder] Add support for distribute constructs #127816
• [MLIR][OpenMP] Host lowering of standalone distribute #127817
• ➡️ [OpenMPIRBuilder] Add support for distribute-parallel-for/do constructs #127818
• [MLIR][OpenMP] Host lowering of distribute-parallel-do/for #127819
• [OpenMPIRBuilder] Split calculation of canonical loop trip count, NFC #127820
• [MLIR][OpenMP] Support target SPMD #127821
• [Flang][OpenMP] Allow host evaluation of loop bounds for distribute #127822

[tblah]

LGTM, thanks

[Meinersbur]

LGTM

[llvm-ci]

LLVM Buildbot has detected a new failure on builder openmp-offload-amdgpu-runtime running on omp-vega20-0 while building llvm at step 6 "test-openmp".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/30/builds/16378

Here is the relevant piece of the build log for the reference

Step 6 (test-openmp) failure: test (failure)
******************** TEST 'libomp :: tasking/issue-94260-2.c' FAILED ********************
Exit Code: -11

Command Output (stdout):
--
# RUN: at line 1
/home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.build/./bin/clang -fopenmp   -I /home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.build/runtimes/runtimes-bins/openmp/runtime/src -I /home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.src/openmp/runtime/test -L /home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.build/runtimes/runtimes-bins/openmp/runtime/src  -fno-omit-frame-pointer -I /home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.src/openmp/runtime/test/ompt /home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.src/openmp/runtime/test/tasking/issue-94260-2.c -o /home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.build/runtimes/runtimes-bins/openmp/runtime/test/tasking/Output/issue-94260-2.c.tmp -lm -latomic && /home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.build/runtimes/runtimes-bins/openmp/runtime/test/tasking/Output/issue-94260-2.c.tmp
# executed command: /home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.build/./bin/clang -fopenmp -I /home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.build/runtimes/runtimes-bins/openmp/runtime/src -I /home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.src/openmp/runtime/test -L /home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.build/runtimes/runtimes-bins/openmp/runtime/src -fno-omit-frame-pointer -I /home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.src/openmp/runtime/test/ompt /home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.src/openmp/runtime/test/tasking/issue-94260-2.c -o /home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.build/runtimes/runtimes-bins/openmp/runtime/test/tasking/Output/issue-94260-2.c.tmp -lm -latomic
# note: command had no output on stdout or stderr
# executed command: /home/ompworker/bbot/openmp-offload-amdgpu-runtime/llvm.build/runtimes/runtimes-bins/openmp/runtime/test/tasking/Output/issue-94260-2.c.tmp
# note: command had no output on stdout or stderr
# error: command failed with exit status: -11

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