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[llvm][mlir][OpenMP] Support translation for linear clause in omp.wsloop and omp.simd #139386

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[llvm][mlir][OpenMP] Support translation for linear clause in omp.wsloop and omp.simd #139386

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[flang][OpenMP] Support MLIR lowering of linear clause for omp.wsloop
NimishMishra Jul 9, 2025
29ba59e
Tests
NimishMishra Jul 9, 2025
39ca840
Add more tests
NimishMishra Jul 9, 2025
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7 changes: 3 additions & 4 deletions flang/lib/Lower/OpenMP/OpenMP.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1816,8 +1816,7 @@ static void genSimdClauses(
cp.processReduction(loc, clauseOps, reductionSyms);
cp.processSafelen(clauseOps);
cp.processSimdlen(clauseOps);

cp.processTODO<clause::Linear>(loc, llvm::omp::Directive::OMPD_simd);
cp.processLinear(clauseOps);
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The current implementation of processLinear does not seem to guarantee that the variable comes from an alloca. For example what if it is a function argument?

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I ran some tests, and the semantic checks were able to catch those cases. For instance, if the linear variable is anything other than an integer type, we get a semantic error noting that a linear variable with the REF modifier needs to be of integer type.

Do you think we should nevertheless add a check during FIR gen? I added a check during the translation but skipped adding it during FIR gen because of this reason.

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subroutine test(lin, lb, ub, step)
  integer :: lin, lb, ub, step, i

  !$omp do linear(lin)
  do i = lb,ub,step
    l = l + 2
  enddo
endsubroutine

}

static void genSingleClauses(lower::AbstractConverter &converter,
Expand Down Expand Up @@ -2007,9 +2006,9 @@ static void genWsloopClauses(
cp.processOrdered(clauseOps);
cp.processReduction(loc, clauseOps, reductionSyms);
cp.processSchedule(stmtCtx, clauseOps);
cp.processLinear(clauseOps);

cp.processTODO<clause::Allocate, clause::Linear>(
loc, llvm::omp::Directive::OMPD_do);
cp.processTODO<clause::Allocate>(loc, llvm::omp::Directive::OMPD_do);
}

//===----------------------------------------------------------------------===//
Expand Down
14 changes: 0 additions & 14 deletions flang/test/Lower/OpenMP/Todo/omp-do-simd-linear.f90
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54 changes: 54 additions & 0 deletions flang/test/Lower/OpenMP/simd-linear.f90
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Original file line number Diff line number Diff line change
@@ -0,0 +1,54 @@
! This test checks lowering of OpenMP DO Directive (Worksharing)
! with linear clause

! RUN: %flang_fc1 -fopenmp -emit-hlfir %s -o - 2>&1 | FileCheck %s

!CHECK: %[[X_alloca:.*]] = fir.alloca i32 {bindc_name = "x", uniq_name = "_QFsimple_linearEx"}
!CHECK: %[[X:.*]]:2 = hlfir.declare %[[X_alloca]] {uniq_name = "_QFsimple_linearEx"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
!CHECK: %[[const:.*]] = arith.constant 1 : i32
subroutine simple_linear
implicit none
integer :: x, y, i
!CHECK: omp.simd linear(%[[X]]#0 = %[[const]] : !fir.ref<i32>) {{.*}}
!$omp simd linear(x)
!CHECK: %[[LOAD:.*]] = fir.load %[[X]]#0 : !fir.ref<i32>
!CHECK: %[[const:.*]] = arith.constant 2 : i32
!CHECK: %[[RESULT:.*]] = arith.addi %[[LOAD]], %[[const]] : i32
do i = 1, 10
y = x + 2
end do
end subroutine


!CHECK: %[[X_alloca:.*]] = fir.alloca i32 {bindc_name = "x", uniq_name = "_QFlinear_stepEx"}
!CHECK: %[[X:.*]]:2 = hlfir.declare %[[X_alloca]] {uniq_name = "_QFlinear_stepEx"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
subroutine linear_step
implicit none
integer :: x, y, i
!CHECK: %[[const:.*]] = arith.constant 4 : i32
!CHECK: omp.simd linear(%[[X]]#0 = %[[const]] : !fir.ref<i32>) {{.*}}
!$omp simd linear(x:4)
!CHECK: %[[LOAD:.*]] = fir.load %[[X]]#0 : !fir.ref<i32>
!CHECK: %[[const:.*]] = arith.constant 2 : i32
!CHECK: %[[RESULT:.*]] = arith.addi %[[LOAD]], %[[const]] : i32
do i = 1, 10
y = x + 2
end do
end subroutine

!CHECK: %[[A_alloca:.*]] = fir.alloca i32 {bindc_name = "a", uniq_name = "_QFlinear_exprEa"}
!CHECK: %[[A:.*]]:2 = hlfir.declare %[[A_alloca]] {uniq_name = "_QFlinear_exprEa"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
!CHECK: %[[X_alloca:.*]] = fir.alloca i32 {bindc_name = "x", uniq_name = "_QFlinear_exprEx"}
!CHECK: %[[X:.*]]:2 = hlfir.declare %[[X_alloca]] {uniq_name = "_QFlinear_exprEx"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
subroutine linear_expr
implicit none
integer :: x, y, i, a
!CHECK: %[[LOAD_A:.*]] = fir.load %[[A]]#0 : !fir.ref<i32>
!CHECK: %[[const:.*]] = arith.constant 4 : i32
!CHECK: %[[LINEAR_EXPR:.*]] = arith.addi %[[LOAD_A]], %[[const]] : i32
!CHECK: omp.simd linear(%[[X]]#0 = %[[LINEAR_EXPR]] : !fir.ref<i32>) {{.*}}
!$omp simd linear(x:a+4)
do i = 1, 10
y = x + 2
end do
end subroutine
57 changes: 57 additions & 0 deletions flang/test/Lower/OpenMP/wsloop-linear.f90
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@@ -0,0 +1,57 @@
! This test checks lowering of OpenMP DO Directive (Worksharing)
! with linear clause

! RUN: %flang_fc1 -fopenmp -emit-hlfir %s -o - 2>&1 | FileCheck %s

!CHECK: %[[X_alloca:.*]] = fir.alloca i32 {bindc_name = "x", uniq_name = "_QFsimple_linearEx"}
!CHECK: %[[X:.*]]:2 = hlfir.declare %[[X_alloca]] {uniq_name = "_QFsimple_linearEx"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
!CHECK: %[[const:.*]] = arith.constant 1 : i32
subroutine simple_linear
implicit none
integer :: x, y, i
!CHECK: omp.wsloop linear(%[[X]]#0 = %[[const]] : !fir.ref<i32>) {{.*}}
!$omp do linear(x)
!CHECK: %[[LOAD:.*]] = fir.load %[[X]]#0 : !fir.ref<i32>
!CHECK: %[[const:.*]] = arith.constant 2 : i32
!CHECK: %[[RESULT:.*]] = arith.addi %[[LOAD]], %[[const]] : i32
do i = 1, 10
y = x + 2
end do
!$omp end do
end subroutine


!CHECK: %[[X_alloca:.*]] = fir.alloca i32 {bindc_name = "x", uniq_name = "_QFlinear_stepEx"}
!CHECK: %[[X:.*]]:2 = hlfir.declare %[[X_alloca]] {uniq_name = "_QFlinear_stepEx"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
subroutine linear_step
implicit none
integer :: x, y, i
!CHECK: %[[const:.*]] = arith.constant 4 : i32
!CHECK: omp.wsloop linear(%[[X]]#0 = %[[const]] : !fir.ref<i32>) {{.*}}
!$omp do linear(x:4)
!CHECK: %[[LOAD:.*]] = fir.load %[[X]]#0 : !fir.ref<i32>
!CHECK: %[[const:.*]] = arith.constant 2 : i32
!CHECK: %[[RESULT:.*]] = arith.addi %[[LOAD]], %[[const]] : i32
do i = 1, 10
y = x + 2
end do
!$omp end do
end subroutine

!CHECK: %[[A_alloca:.*]] = fir.alloca i32 {bindc_name = "a", uniq_name = "_QFlinear_exprEa"}
!CHECK: %[[A:.*]]:2 = hlfir.declare %[[A_alloca]] {uniq_name = "_QFlinear_exprEa"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
!CHECK: %[[X_alloca:.*]] = fir.alloca i32 {bindc_name = "x", uniq_name = "_QFlinear_exprEx"}
!CHECK: %[[X:.*]]:2 = hlfir.declare %[[X_alloca]] {uniq_name = "_QFlinear_exprEx"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
subroutine linear_expr
implicit none
integer :: x, y, i, a
!CHECK: %[[LOAD_A:.*]] = fir.load %[[A]]#0 : !fir.ref<i32>
!CHECK: %[[const:.*]] = arith.constant 4 : i32
!CHECK: %[[LINEAR_EXPR:.*]] = arith.addi %[[LOAD_A]], %[[const]] : i32
!CHECK: omp.wsloop linear(%[[X]]#0 = %[[LINEAR_EXPR]] : !fir.ref<i32>) {{.*}}
!$omp do linear(x:a+4)
do i = 1, 10
y = x + 2
end do
!$omp end do
end subroutine
2 changes: 1 addition & 1 deletion mlir/lib/Dialect/OpenMP/IR/OpenMPDialect.cpp
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Expand Up @@ -2608,7 +2608,7 @@ void SimdOp::build(OpBuilder &builder, OperationState &state,
// TODO Store clauses in op: linearVars, linearStepVars
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Suggested change
// TODO Store clauses in op: linearVars, linearStepVars

SimdOp::build(builder, state, clauses.alignedVars,
makeArrayAttr(ctx, clauses.alignments), clauses.ifExpr,
/*linear_vars=*/{}, /*linear_step_vars=*/{},
clauses.linearVars, clauses.linearStepVars,
clauses.nontemporalVars, clauses.order, clauses.orderMod,
clauses.privateVars, makeArrayAttr(ctx, clauses.privateSyms),
clauses.privateNeedsBarrier, clauses.reductionMod,
Expand Down
98 changes: 62 additions & 36 deletions mlir/lib/Target/LLVMIR/Dialect/OpenMP/OpenMPToLLVMIRTranslation.cpp
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Expand Up @@ -147,9 +147,9 @@ class LinearClauseProcessor {

public:
// Allocate space for linear variabes
void createLinearVar(llvm::IRBuilderBase &builder,
LLVM::ModuleTranslation &moduleTranslation,
mlir::Value &linearVar) {
LogicalResult createLinearVar(llvm::IRBuilderBase &builder,
LLVM::ModuleTranslation &moduleTranslation,
mlir::Value &linearVar, Operation &op) {
if (llvm::AllocaInst *linearVarAlloca = dyn_cast<llvm::AllocaInst>(
moduleTranslation.lookupValue(linearVar))) {
linearPreconditionVars.push_back(builder.CreateAlloca(
Expand All @@ -159,7 +159,12 @@ class LinearClauseProcessor {
linearOrigVal.push_back(moduleTranslation.lookupValue(linearVar));
linearLoopBodyTemps.push_back(linearLoopBodyTemp);
linearOrigVars.push_back(linearVarAlloca);
return success();
}

else
return op.emitError() << "not yet implemented: linear clause support"
<< " for non alloca linear variables";
}

// Initialize linear step
Expand All @@ -169,20 +174,15 @@ class LinearClauseProcessor {
}

// Emit IR for initialization of linear variables
llvm::OpenMPIRBuilder::InsertPointOrErrorTy
initLinearVar(llvm::IRBuilderBase &builder,
LLVM::ModuleTranslation &moduleTranslation,
llvm::BasicBlock *loopPreHeader) {
void initLinearVar(llvm::IRBuilderBase &builder,
LLVM::ModuleTranslation &moduleTranslation,
llvm::BasicBlock *loopPreHeader) {
builder.SetInsertPoint(loopPreHeader->getTerminator());
for (size_t index = 0; index < linearOrigVars.size(); index++) {
llvm::LoadInst *linearVarLoad = builder.CreateLoad(
linearOrigVars[index]->getAllocatedType(), linearOrigVars[index]);
builder.CreateStore(linearVarLoad, linearPreconditionVars[index]);
}
llvm::OpenMPIRBuilder::InsertPointOrErrorTy afterBarrierIP =
moduleTranslation.getOpenMPBuilder()->createBarrier(
builder.saveIP(), llvm::omp::OMPD_barrier);
return afterBarrierIP;
}

// Emit IR for updating Linear variables
Expand All @@ -193,18 +193,27 @@ class LinearClauseProcessor {
// Emit increments for linear vars
llvm::LoadInst *linearVarStart =
builder.CreateLoad(linearOrigVars[index]->getAllocatedType(),

linearPreconditionVars[index]);

auto mulInst = builder.CreateMul(loopInductionVar, linearSteps[index]);
auto addInst = builder.CreateAdd(linearVarStart, mulInst);
builder.CreateStore(addInst, linearLoopBodyTemps[index]);
if (linearOrigVars[index]->getAllocatedType()->isIntegerTy()) {
auto addInst = builder.CreateAdd(linearVarStart, mulInst);
builder.CreateStore(addInst, linearLoopBodyTemps[index]);
} else if (linearOrigVars[index]
->getAllocatedType()
->isFloatingPointTy()) {
auto cvt = builder.CreateSIToFP(
mulInst, linearOrigVars[index]->getAllocatedType());
auto addInst = builder.CreateFAdd(linearVarStart, cvt);
builder.CreateStore(addInst, linearLoopBodyTemps[index]);
}
}
}

// Linear variable finalization is conditional on the last logical iteration.
// Create BB splits to manage the same.
void outlineLinearFinalizationBB(llvm::IRBuilderBase &builder,
llvm::BasicBlock *loopExit) {
void splitLinearFiniBB(llvm::IRBuilderBase &builder,
llvm::BasicBlock *loopExit) {
linearFinalizationBB = loopExit->splitBasicBlock(
loopExit->getTerminator(), "omp_loop.linear_finalization");
linearExitBB = linearFinalizationBB->splitBasicBlock(
Expand Down Expand Up @@ -339,10 +348,6 @@ static LogicalResult checkImplementationStatus(Operation &op) {
if (!op.getIsDevicePtrVars().empty())
result = todo("is_device_ptr");
};
auto checkLinear = [&todo](auto op, LogicalResult &result) {
if (!op.getLinearVars().empty() || !op.getLinearStepVars().empty())
result = todo("linear");
};
auto checkNowait = [&todo](auto op, LogicalResult &result) {
if (op.getNowait())
result = todo("nowait");
Expand Down Expand Up @@ -432,18 +437,14 @@ static LogicalResult checkImplementationStatus(Operation &op) {
})
.Case([&](omp::WsloopOp op) {
checkAllocate(op, result);
checkLinear(op, result);
checkOrder(op, result);
checkReduction(op, result);
})
.Case([&](omp::ParallelOp op) {
checkAllocate(op, result);
checkReduction(op, result);
})
.Case([&](omp::SimdOp op) {
checkLinear(op, result);
checkReduction(op, result);
})
.Case([&](omp::SimdOp op) { checkReduction(op, result); })
.Case<omp::AtomicReadOp, omp::AtomicWriteOp, omp::AtomicUpdateOp,
omp::AtomicCaptureOp>([&](auto op) { checkHint(op, result); })
.Case<omp::TargetEnterDataOp, omp::TargetExitDataOp, omp::TargetUpdateOp>(
Expand Down Expand Up @@ -2587,13 +2588,13 @@ convertOmpWsloop(Operation &opInst, llvm::IRBuilderBase &builder,

// Initialize linear variables and linear step
LinearClauseProcessor linearClauseProcessor;
if (wsloopOp.getLinearVars().size()) {
for (mlir::Value linearVar : wsloopOp.getLinearVars())
linearClauseProcessor.createLinearVar(builder, moduleTranslation,
linearVar);
for (mlir::Value linearStep : wsloopOp.getLinearStepVars())
linearClauseProcessor.initLinearStep(moduleTranslation, linearStep);
for (mlir::Value linearVar : wsloopOp.getLinearVars()) {
if (failed(linearClauseProcessor.createLinearVar(builder, moduleTranslation,
linearVar, opInst)))
return failure();
}
for (mlir::Value linearStep : wsloopOp.getLinearStepVars())
linearClauseProcessor.initLinearStep(moduleTranslation, linearStep);

llvm::Expected<llvm::BasicBlock *> regionBlock = convertOmpOpRegions(
wsloopOp.getRegion(), "omp.wsloop.region", builder, moduleTranslation);
Expand All @@ -2605,16 +2606,17 @@ convertOmpWsloop(Operation &opInst, llvm::IRBuilderBase &builder,

// Emit Initialization and Update IR for linear variables
if (wsloopOp.getLinearVars().size()) {
linearClauseProcessor.initLinearVar(builder, moduleTranslation,
loopInfo->getPreheader());
llvm::OpenMPIRBuilder::InsertPointOrErrorTy afterBarrierIP =
linearClauseProcessor.initLinearVar(builder, moduleTranslation,
loopInfo->getPreheader());
moduleTranslation.getOpenMPBuilder()->createBarrier(
builder.saveIP(), llvm::omp::OMPD_barrier);
if (failed(handleError(afterBarrierIP, *loopOp)))
return failure();
builder.restoreIP(*afterBarrierIP);
linearClauseProcessor.updateLinearVar(builder, loopInfo->getBody(),
loopInfo->getIndVar());
linearClauseProcessor.outlineLinearFinalizationBB(builder,
loopInfo->getExit());
linearClauseProcessor.splitLinearFiniBB(builder, loopInfo->getExit());
}

builder.SetInsertPoint(*regionBlock, (*regionBlock)->begin());
Expand Down Expand Up @@ -2882,6 +2884,17 @@ convertOmpSimd(Operation &opInst, llvm::IRBuilderBase &builder,
llvm::OpenMPIRBuilder::InsertPointTy allocaIP =
findAllocaInsertPoint(builder, moduleTranslation);

// Create linear variables and initialize linear step
LinearClauseProcessor linearClauseProcessor;

for (mlir::Value linearVar : simdOp.getLinearVars()) {
if (failed(linearClauseProcessor.createLinearVar(builder, moduleTranslation,
linearVar, opInst)))
return failure();
}
for (mlir::Value linearStep : simdOp.getLinearStepVars())
linearClauseProcessor.initLinearStep(moduleTranslation, linearStep);

llvm::Expected<llvm::BasicBlock *> afterAllocas = allocatePrivateVars(
builder, moduleTranslation, privateVarsInfo, allocaIP);
if (handleError(afterAllocas, opInst).failed())
Expand Down Expand Up @@ -2945,14 +2958,27 @@ convertOmpSimd(Operation &opInst, llvm::IRBuilderBase &builder,
if (failed(handleError(regionBlock, opInst)))
return failure();

builder.SetInsertPoint(*regionBlock, (*regionBlock)->begin());
llvm::CanonicalLoopInfo *loopInfo = findCurrentLoopInfo(moduleTranslation);

// Emit Initialization for linear variables
if (simdOp.getLinearVars().size()) {
linearClauseProcessor.initLinearVar(builder, moduleTranslation,
loopInfo->getPreheader());
linearClauseProcessor.updateLinearVar(builder, loopInfo->getBody(),
loopInfo->getIndVar());
}
builder.SetInsertPoint(*regionBlock, (*regionBlock)->begin());

ompBuilder->applySimd(loopInfo, alignedVars,
simdOp.getIfExpr()
? moduleTranslation.lookupValue(simdOp.getIfExpr())
: nullptr,
order, simdlen, safelen);

for (size_t index = 0; index < simdOp.getLinearVars().size(); index++)
linearClauseProcessor.rewriteInPlace(builder, "omp.loop_nest.region",
index);

// We now need to reduce the per-simd-lane reduction variable into the
// original variable. This works a bit differently to other reductions (e.g.
// wsloop) because we don't need to call into the OpenMP runtime to handle
Expand Down
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