[Mlir-commits] [llvm] [mlir] [MLIR][OpenMP] Remove Generic-SPMD early detection (PR #150922)
Sergio Afonso
llvmlistbot at llvm.org
Mon Apr 27 04:45:13 PDT 2026
https://github.com/skatrak updated https://github.com/llvm/llvm-project/pull/150922
>From 0524485bea2a22c62042d60f7f4f0a5bdd24eb08 Mon Sep 17 00:00:00 2001
From: Sergio Afonso <safonsof at amd.com>
Date: Wed, 21 May 2025 16:29:23 +0100
Subject: [PATCH] [MLIR][OpenMP] Remove Generic-SPMD early detection
This patch removes logic from MLIR to attempt identifying Generic kernels that
could be executed in SPMD mode.
This optimization is done by the OpenMPOpt pass for Clang and is only required
here to circumvent missing support for the new DeviceRTL APIs used in MLIR to
LLVM IR translation that Clang doesn't currently use (e.g.
`kmpc_distribute_static_loop`). Removing checks in MLIR avoids duplicating the
logic that should be centralized in the OpenMPOpt pass.
Additionally, offloading kernels currently compiled through the OpenMP dialect
fail to run parallel regions properly when in Generic mode. By disabling early
detection, this issue becomes apparent for a range of kernels where this was
masked by having them run in SPMD mode.
---
llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp | 3 +-
.../mlir/Dialect/OpenMP/OpenMPEnums.td | 36 ++++-----
mlir/include/mlir/Dialect/OpenMP/OpenMPOps.td | 12 ++-
mlir/lib/Dialect/OpenMP/IR/OpenMPDialect.cpp | 77 ++++++++-----------
.../OpenMP/OpenMPToLLVMIRTranslation.cpp | 44 +++++------
.../LLVMIR/openmp-target-generic-spmd.mlir | 2 +-
6 files changed, 73 insertions(+), 101 deletions(-)
diff --git a/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp b/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp
index 125620bd49502..e42b5a2d696f3 100644
--- a/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp
+++ b/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp
@@ -7844,7 +7844,8 @@ OpenMPIRBuilder::InsertPointTy OpenMPIRBuilder::createTargetInit(
Constant *Ident = getOrCreateIdent(SrcLocStr, SrcLocStrSize);
Constant *IsSPMDVal = ConstantInt::getSigned(Int8, Attrs.ExecFlags);
Constant *UseGenericStateMachineVal = ConstantInt::getSigned(
- Int8, Attrs.ExecFlags != omp::OMP_TGT_EXEC_MODE_SPMD);
+ Int8, Attrs.ExecFlags != omp::OMP_TGT_EXEC_MODE_SPMD &&
+ Attrs.ExecFlags != omp::OMP_TGT_EXEC_MODE_SPMD_NO_LOOP);
Constant *MayUseNestedParallelismVal = ConstantInt::getSigned(Int8, true);
Constant *DebugIndentionLevelVal = ConstantInt::getSigned(Int16, 0);
diff --git a/mlir/include/mlir/Dialect/OpenMP/OpenMPEnums.td b/mlir/include/mlir/Dialect/OpenMP/OpenMPEnums.td
index 06c5e0b89ff05..6c649f4243f13 100644
--- a/mlir/include/mlir/Dialect/OpenMP/OpenMPEnums.td
+++ b/mlir/include/mlir/Dialect/OpenMP/OpenMPEnums.td
@@ -297,31 +297,21 @@ def ScheduleModifier : OpenMP_I32EnumAttr<
def ScheduleModifierAttr : OpenMP_EnumAttr<ScheduleModifier, "sched_mod">;
//===----------------------------------------------------------------------===//
-// target_region_flags enum.
+// target_exec_mode enum.
//===----------------------------------------------------------------------===//
-def TargetRegionFlagsNone : I32BitEnumAttrCaseNone<"none">;
-def TargetRegionFlagsGeneric : I32BitEnumAttrCaseBit<"generic", 0>;
-def TargetRegionFlagsSpmd : I32BitEnumAttrCaseBit<"spmd", 1>;
-def TargetRegionFlagsTripCount : I32BitEnumAttrCaseBit<"trip_count", 2>;
-def TargetRegionFlagsNoLoop : I32BitEnumAttrCaseBit<"no_loop", 3>;
-
-def TargetRegionFlags : OpenMP_BitEnumAttr<
- "TargetRegionFlags",
- "These flags describe properties of the target kernel. "
- "TargetRegionFlagsGeneric - denotes generic kernel. "
- "TargetRegionFlagsSpmd - denotes SPMD kernel. "
- "TargetRegionFlagsNoLoop - denotes kernel where "
- "num_teams * num_threads >= loop_trip_count. It allows the conversion "
- "of loops into sequential code by ensuring that each team/thread "
- "executes at most one iteration. "
- "TargetRegionFlagsTripCount - checks if the loop trip count should be "
- "calculated.", [
- TargetRegionFlagsNone,
- TargetRegionFlagsGeneric,
- TargetRegionFlagsSpmd,
- TargetRegionFlagsTripCount,
- TargetRegionFlagsNoLoop
+def TargetExecModeBare : I32EnumAttrCase<"bare", 0>;
+def TargetExecModeGeneric : I32EnumAttrCase<"generic", 1>;
+def TargetExecModeSpmd : I32EnumAttrCase<"spmd", 2>;
+def TargetExecModeSpmdNoLoop : I32EnumAttrCase<"no_loop", 3>;
+
+def TargetExecMode : OpenMP_I32EnumAttr<
+ "TargetExecMode",
+ "target execution mode, mirroring the `OMPTgtExecModeFlags` LLVM enum", [
+ TargetExecModeBare,
+ TargetExecModeGeneric,
+ TargetExecModeSpmd,
+ TargetExecModeSpmdNoLoop,
]>;
//===----------------------------------------------------------------------===//
diff --git a/mlir/include/mlir/Dialect/OpenMP/OpenMPOps.td b/mlir/include/mlir/Dialect/OpenMP/OpenMPOps.td
index 1931c91080644..cffa3a9a3e752 100644
--- a/mlir/include/mlir/Dialect/OpenMP/OpenMPOps.td
+++ b/mlir/include/mlir/Dialect/OpenMP/OpenMPOps.td
@@ -1605,13 +1605,17 @@ def TargetOp : OpenMP_Op<"target", traits = [
/// operations, the top level one will be the one captured.
Operation *getInnermostCapturedOmpOp();
- /// Infers the kernel type (Generic, SPMD or Generic-SPMD) based on the
- /// contents of the target region.
+ /// Infers the kernel type (Bare, Generic or SPMD) based on the contents of
+ /// the target region.
///
/// \param capturedOp result of a still valid (no modifications made to any
/// nested operations) previous call to `getInnermostCapturedOmpOp()`.
- static ::mlir::omp::TargetRegionFlags
- getKernelExecFlags(Operation *capturedOp);
+ /// \param hostEvalTripCount output argument to store whether this kernel
+ /// wraps a loop whose bounds must be evaluated on the host prior to
+ /// launching it.
+ static ::mlir::omp::TargetExecMode
+ getKernelExecFlags(Operation *capturedOp,
+ bool *hostEvalTripCount = nullptr);
}] # clausesExtraClassDeclaration;
let assemblyFormat = clausesAssemblyFormat # [{
diff --git a/mlir/lib/Dialect/OpenMP/IR/OpenMPDialect.cpp b/mlir/lib/Dialect/OpenMP/IR/OpenMPDialect.cpp
index 691793b50d33d..d8ddf7f0407cb 100644
--- a/mlir/lib/Dialect/OpenMP/IR/OpenMPDialect.cpp
+++ b/mlir/lib/Dialect/OpenMP/IR/OpenMPDialect.cpp
@@ -2406,8 +2406,9 @@ LogicalResult TargetOp::verifyRegions() {
return emitError("target containing multiple 'omp.teams' nested ops");
// Check that host_eval values are only used in legal ways.
+ bool hostEvalTripCount;
Operation *capturedOp = getInnermostCapturedOmpOp();
- TargetRegionFlags execFlags = getKernelExecFlags(capturedOp);
+ TargetExecMode execMode = getKernelExecFlags(capturedOp, &hostEvalTripCount);
for (Value hostEvalArg :
cast<BlockArgOpenMPOpInterface>(getOperation()).getHostEvalBlockArgs()) {
for (Operation *user : hostEvalArg.getUsers()) {
@@ -2422,7 +2423,7 @@ LogicalResult TargetOp::verifyRegions() {
"and 'thread_limit' in 'omp.teams'";
}
if (auto parallelOp = dyn_cast<ParallelOp>(user)) {
- if (bitEnumContainsAny(execFlags, TargetRegionFlags::spmd) &&
+ if (execMode == TargetExecMode::spmd &&
parallelOp->isAncestor(capturedOp) &&
llvm::is_contained(parallelOp.getNumThreadsVars(), hostEvalArg))
continue;
@@ -2432,8 +2433,7 @@ LogicalResult TargetOp::verifyRegions() {
"'omp.parallel' when representing target SPMD";
}
if (auto loopNestOp = dyn_cast<LoopNestOp>(user)) {
- if (bitEnumContainsAny(execFlags, TargetRegionFlags::trip_count) &&
- loopNestOp.getOperation() == capturedOp &&
+ if (hostEvalTripCount && loopNestOp.getOperation() == capturedOp &&
(llvm::is_contained(loopNestOp.getLoopLowerBounds(), hostEvalArg) ||
llvm::is_contained(loopNestOp.getLoopUpperBounds(), hostEvalArg) ||
llvm::is_contained(loopNestOp.getLoopSteps(), hostEvalArg)))
@@ -2563,7 +2563,9 @@ static bool canPromoteToNoLoop(Operation *capturedOp, TeamsOp teamsOp,
ompFlags.getAssumeThreadsOversubscription();
}
-TargetRegionFlags TargetOp::getKernelExecFlags(Operation *capturedOp) {
+TargetExecMode TargetOp::getKernelExecFlags(Operation *capturedOp,
+ bool *hostEvalTripCount) {
+ // TODO: Support detection of bare kernel mode.
// A non-null captured op is only valid if it resides inside of a TargetOp
// and is the result of calling getInnermostCapturedOmpOp() on it.
TargetOp targetOp =
@@ -2572,9 +2574,12 @@ TargetRegionFlags TargetOp::getKernelExecFlags(Operation *capturedOp) {
(targetOp && targetOp.getInnermostCapturedOmpOp() == capturedOp)) &&
"unexpected captured op");
+ if (hostEvalTripCount)
+ *hostEvalTripCount = false;
+
// If it's not capturing a loop, it's a default target region.
if (!isa_and_present<LoopNestOp>(capturedOp))
- return TargetRegionFlags::generic;
+ return TargetExecMode::generic;
// Get the innermost non-simd loop wrapper.
SmallVector<LoopWrapperInterface> loopWrappers;
@@ -2587,31 +2592,32 @@ TargetRegionFlags TargetOp::getKernelExecFlags(Operation *capturedOp) {
auto numWrappers = std::distance(innermostWrapper, loopWrappers.end());
if (numWrappers != 1 && numWrappers != 2)
- return TargetRegionFlags::generic;
+ return TargetExecMode::generic;
// Detect target-teams-distribute-parallel-wsloop[-simd].
if (numWrappers == 2) {
WsloopOp *wsloopOp = dyn_cast<WsloopOp>(innermostWrapper);
if (!wsloopOp)
- return TargetRegionFlags::generic;
+ return TargetExecMode::generic;
innermostWrapper = std::next(innermostWrapper);
if (!isa<DistributeOp>(innermostWrapper))
- return TargetRegionFlags::generic;
+ return TargetExecMode::generic;
Operation *parallelOp = (*innermostWrapper)->getParentOp();
if (!isa_and_present<ParallelOp>(parallelOp))
- return TargetRegionFlags::generic;
+ return TargetExecMode::generic;
TeamsOp teamsOp = dyn_cast<TeamsOp>(parallelOp->getParentOp());
if (!teamsOp)
- return TargetRegionFlags::generic;
+ return TargetExecMode::generic;
if (teamsOp->getParentOp() == targetOp.getOperation()) {
- TargetRegionFlags result =
- TargetRegionFlags::spmd | TargetRegionFlags::trip_count;
+ TargetExecMode result = TargetExecMode::spmd;
if (canPromoteToNoLoop(capturedOp, teamsOp, wsloopOp))
- result = result | TargetRegionFlags::no_loop;
+ result = TargetExecMode::no_loop;
+ if (hostEvalTripCount)
+ *hostEvalTripCount = true;
return result;
}
}
@@ -2619,53 +2625,30 @@ TargetRegionFlags TargetOp::getKernelExecFlags(Operation *capturedOp) {
else if (isa<DistributeOp, LoopOp>(innermostWrapper)) {
Operation *teamsOp = (*innermostWrapper)->getParentOp();
if (!isa_and_present<TeamsOp>(teamsOp))
- return TargetRegionFlags::generic;
+ return TargetExecMode::generic;
if (teamsOp->getParentOp() != targetOp.getOperation())
- return TargetRegionFlags::generic;
+ return TargetExecMode::generic;
- if (isa<LoopOp>(innermostWrapper))
- return TargetRegionFlags::spmd | TargetRegionFlags::trip_count;
-
- // Find single immediately nested captured omp.parallel and add spmd flag
- // (generic-spmd case).
- //
- // TODO: This shouldn't have to be done here, as it is too easy to break.
- // The openmp-opt pass should be updated to be able to promote kernels like
- // this from "Generic" to "Generic-SPMD". However, the use of the
- // `kmpc_distribute_static_loop` family of functions produced by the
- // OMPIRBuilder for these kernels prevents that from working.
- Dialect *ompDialect = targetOp->getDialect();
- Operation *nestedCapture = findCapturedOmpOp(
- capturedOp, /*checkSingleMandatoryExec=*/false,
- [&](Operation *sibling) {
- return sibling && (ompDialect != sibling->getDialect() ||
- sibling->hasTrait<OpTrait::IsTerminator>());
- });
-
- TargetRegionFlags result =
- TargetRegionFlags::generic | TargetRegionFlags::trip_count;
-
- if (!nestedCapture)
- return result;
+ if (hostEvalTripCount)
+ *hostEvalTripCount = true;
- while (nestedCapture->getParentOp() != capturedOp)
- nestedCapture = nestedCapture->getParentOp();
+ if (isa<LoopOp>(innermostWrapper))
+ return TargetExecMode::spmd;
- return isa<ParallelOp>(nestedCapture) ? result | TargetRegionFlags::spmd
- : result;
+ return TargetExecMode::generic;
}
// Detect target-parallel-wsloop[-simd].
else if (isa<WsloopOp>(innermostWrapper)) {
Operation *parallelOp = (*innermostWrapper)->getParentOp();
if (!isa_and_present<ParallelOp>(parallelOp))
- return TargetRegionFlags::generic;
+ return TargetExecMode::generic;
if (parallelOp->getParentOp() == targetOp.getOperation())
- return TargetRegionFlags::spmd;
+ return TargetExecMode::spmd;
}
- return TargetRegionFlags::generic;
+ return TargetExecMode::generic;
}
//===----------------------------------------------------------------------===//
diff --git a/mlir/lib/Target/LLVMIR/Dialect/OpenMP/OpenMPToLLVMIRTranslation.cpp b/mlir/lib/Target/LLVMIR/Dialect/OpenMP/OpenMPToLLVMIRTranslation.cpp
index 8614aed1ab80c..1e944ac93e6f1 100644
--- a/mlir/lib/Target/LLVMIR/Dialect/OpenMP/OpenMPToLLVMIRTranslation.cpp
+++ b/mlir/lib/Target/LLVMIR/Dialect/OpenMP/OpenMPToLLVMIRTranslation.cpp
@@ -3643,13 +3643,8 @@ convertOmpWsloop(Operation &opInst, llvm::IRBuilderBase &builder,
// for every omp.wsloop nested inside a no-loop SPMD target region, even if
// that loop is not the top-level SPMD one.
if (loopOp == targetCapturedOp) {
- omp::TargetRegionFlags kernelFlags =
- targetOp.getKernelExecFlags(targetCapturedOp);
- if (omp::bitEnumContainsAll(kernelFlags,
- omp::TargetRegionFlags::spmd |
- omp::TargetRegionFlags::no_loop) &&
- !omp::bitEnumContainsAny(kernelFlags,
- omp::TargetRegionFlags::generic))
+ if (targetOp.getKernelExecFlags(targetCapturedOp) ==
+ omp::TargetExecMode::no_loop)
noLoopMode = true;
}
}
@@ -6936,23 +6931,21 @@ initTargetDefaultAttrs(omp::TargetOp targetOp, Operation *capturedOp,
}
// Update kernel bounds structure for the `OpenMPIRBuilder` to use.
- omp::TargetRegionFlags kernelFlags = targetOp.getKernelExecFlags(capturedOp);
- assert(
- omp::bitEnumContainsAny(kernelFlags, omp::TargetRegionFlags::generic |
- omp::TargetRegionFlags::spmd) &&
- "invalid kernel flags");
- attrs.ExecFlags =
- omp::bitEnumContainsAny(kernelFlags, omp::TargetRegionFlags::generic)
- ? omp::bitEnumContainsAny(kernelFlags, omp::TargetRegionFlags::spmd)
- ? llvm::omp::OMP_TGT_EXEC_MODE_GENERIC_SPMD
- : llvm::omp::OMP_TGT_EXEC_MODE_GENERIC
- : llvm::omp::OMP_TGT_EXEC_MODE_SPMD;
- if (omp::bitEnumContainsAll(kernelFlags,
- omp::TargetRegionFlags::spmd |
- omp::TargetRegionFlags::no_loop) &&
- !omp::bitEnumContainsAny(kernelFlags, omp::TargetRegionFlags::generic))
+ omp::TargetExecMode execMode = targetOp.getKernelExecFlags(capturedOp);
+ switch (execMode) {
+ case omp::TargetExecMode::bare:
+ attrs.ExecFlags = llvm::omp::OMP_TGT_EXEC_MODE_BARE;
+ break;
+ case omp::TargetExecMode::generic:
+ attrs.ExecFlags = llvm::omp::OMP_TGT_EXEC_MODE_GENERIC;
+ break;
+ case omp::TargetExecMode::spmd:
+ attrs.ExecFlags = llvm::omp::OMP_TGT_EXEC_MODE_SPMD;
+ break;
+ case omp::TargetExecMode::no_loop:
attrs.ExecFlags = llvm::omp::OMP_TGT_EXEC_MODE_SPMD_NO_LOOP;
-
+ break;
+ }
attrs.MinTeams = minTeamsVal;
attrs.MaxTeams.front() = maxTeamsVal;
attrs.MinThreads = 1;
@@ -7009,8 +7002,9 @@ initTargetRuntimeAttrs(llvm::IRBuilderBase &builder,
if (numThreads)
attrs.MaxThreads = moduleTranslation.lookupValue(numThreads);
- if (omp::bitEnumContainsAny(targetOp.getKernelExecFlags(capturedOp),
- omp::TargetRegionFlags::trip_count)) {
+ bool hostEvalTripCount;
+ targetOp.getKernelExecFlags(capturedOp, &hostEvalTripCount);
+ if (hostEvalTripCount) {
llvm::OpenMPIRBuilder *ompBuilder = moduleTranslation.getOpenMPBuilder();
attrs.LoopTripCount = nullptr;
diff --git a/mlir/test/Target/LLVMIR/openmp-target-generic-spmd.mlir b/mlir/test/Target/LLVMIR/openmp-target-generic-spmd.mlir
index 5c378173605a4..ecfc2dc7b4598 100644
--- a/mlir/test/Target/LLVMIR/openmp-target-generic-spmd.mlir
+++ b/mlir/test/Target/LLVMIR/openmp-target-generic-spmd.mlir
@@ -84,7 +84,7 @@ module attributes {dlti.dl_spec = #dlti.dl_spec<#dlti.dl_entry<"dlti.alloca_memo
}
}
-// DEVICE: @[[KERNEL_NAME:.*]]_exec_mode = weak protected constant i8 [[EXEC_MODE:3]]
+// DEVICE: @[[KERNEL_NAME:.*]]_exec_mode = weak protected constant i8 [[EXEC_MODE:1]]
// DEVICE: @llvm.compiler.used = appending global [1 x ptr] [ptr @[[KERNEL_NAME]]_exec_mode], section "llvm.metadata"
// DEVICE: @[[KERNEL_NAME]]_kernel_environment = weak_odr protected constant %struct.KernelEnvironmentTy {
// DEVICE-SAME: %struct.ConfigurationEnvironmentTy { i8 1, i8 1, i8 [[EXEC_MODE]], {{.*}}},
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