[Mlir-commits] [mlir] [MLIR][Vector] Add warp distribution for `scf.if` (PR #157119)
llvmlistbot at llvm.org
llvmlistbot at llvm.org
Fri Sep 5 07:55:06 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-mlir
Author: Artem Kroviakov (akroviakov)
<details>
<summary>Changes</summary>
This PR adds `scf.if` op distribution to the existing `VectorDistribute` patterns.
The logic mostly follows that of `scf.for`: move op outside, wrap each branch with `gpu.warp_execute_on_lane_0`.
A notable difference to `scf.for` is that each branch has its own set of escaping values, and `scf.if` itself does not have block arguments.
---
Full diff: https://github.com/llvm/llvm-project/pull/157119.diff
2 Files Affected:
- (modified) mlir/lib/Dialect/Vector/Transforms/VectorDistribute.cpp (+201)
- (modified) mlir/test/Dialect/Vector/vector-warp-distribute.mlir (+69)
``````````diff
diff --git a/mlir/lib/Dialect/Vector/Transforms/VectorDistribute.cpp b/mlir/lib/Dialect/Vector/Transforms/VectorDistribute.cpp
index c84eb2c9f8857..cf5928278aa64 100644
--- a/mlir/lib/Dialect/Vector/Transforms/VectorDistribute.cpp
+++ b/mlir/lib/Dialect/Vector/Transforms/VectorDistribute.cpp
@@ -1713,6 +1713,205 @@ struct WarpOpInsert : public WarpDistributionPattern {
}
};
+struct WarpOpScfIfOp : public WarpDistributionPattern {
+ WarpOpScfIfOp(MLIRContext *ctx, DistributionMapFn fn, PatternBenefit b = 1)
+ : WarpDistributionPattern(ctx, b), distributionMapFn(std::move(fn)) {}
+ LogicalResult matchAndRewrite(WarpExecuteOnLane0Op warpOp,
+ PatternRewriter &rewriter) const override {
+ gpu::YieldOp warpOpYield = warpOp.getTerminator();
+ // Only pick up `IfOp` if it is the last op in the region.
+ Operation *lastNode = warpOpYield->getPrevNode();
+ auto ifOp = dyn_cast_or_null<scf::IfOp>(lastNode);
+ if (!ifOp)
+ return failure();
+
+ // The current `WarpOp` can yield two types of values:
+ // 1. Not results of `IfOp`:
+ // Preserve them in the new `WarpOp`.
+ // Collect their yield index.
+ // 2. Results of `IfOp`:
+ // They are not part of the new `WarpOp` results.
+ // Map current warp's yield operand index to `IfOp` result idx.
+ SmallVector<Value> nonIfYieldValues;
+ SmallVector<unsigned> nonIfYieldIndices;
+ llvm::SmallDenseMap<unsigned, unsigned> ifResultMapping;
+ llvm::SmallDenseMap<unsigned, VectorType> ifResultDistTypes;
+ for (OpOperand &yieldOperand : warpOpYield->getOpOperands()) {
+ const unsigned yieldOperandIdx = yieldOperand.getOperandNumber();
+ if (yieldOperand.get().getDefiningOp() != ifOp.getOperation()) {
+ nonIfYieldValues.push_back(yieldOperand.get());
+ nonIfYieldIndices.push_back(yieldOperandIdx);
+ continue;
+ }
+ OpResult ifResult = cast<OpResult>(yieldOperand.get());
+ const unsigned ifResultIdx = ifResult.getResultNumber();
+ ifResultMapping[yieldOperandIdx] = ifResultIdx;
+ // If this `ifOp` result is vector type and it is yielded by the
+ // `WarpOp`, we keep track the distributed type for this result.
+ if (!isa<VectorType>(ifResult.getType()))
+ continue;
+ VectorType distType =
+ cast<VectorType>(warpOp.getResult(yieldOperandIdx).getType());
+ ifResultDistTypes[ifResultIdx] = distType;
+ }
+
+ // Collect `WarpOp`-defined values used in `ifOp`, the new warp op returns
+ // them
+ auto getEscapingValues = [&](Region &branch,
+ llvm::SmallSetVector<Value, 32> &values,
+ SmallVector<Type> &inputTypes,
+ SmallVector<Type> &distTypes) {
+ if (branch.empty())
+ return;
+ mlir::visitUsedValuesDefinedAbove(branch, [&](OpOperand *operand) {
+ Operation *parent = operand->get().getParentRegion()->getParentOp();
+ if (warpOp->isAncestor(parent)) {
+ if (!values.insert(operand->get()))
+ return;
+ Type distType = operand->get().getType();
+ if (auto vecType = dyn_cast<VectorType>(distType)) {
+ AffineMap map = distributionMapFn(operand->get());
+ distType = getDistributedType(vecType, map, warpOp.getWarpSize());
+ }
+ inputTypes.push_back(operand->get().getType());
+ distTypes.push_back(distType);
+ }
+ });
+ };
+ llvm::SmallSetVector<Value, 32> escapingValuesThen;
+ SmallVector<Type> escapingValueInputTypesThen; // inner warp op block args
+ SmallVector<Type> escapingValueDistTypesThen; // new warp returns
+ getEscapingValues(ifOp.getThenRegion(), escapingValuesThen,
+ escapingValueInputTypesThen, escapingValueDistTypesThen);
+ llvm::SmallSetVector<Value, 32> escapingValuesElse;
+ SmallVector<Type> escapingValueInputTypesElse; // inner warp op block args
+ SmallVector<Type> escapingValueDistTypesElse; // new warp returns
+ getEscapingValues(ifOp.getElseRegion(), escapingValuesElse,
+ escapingValueInputTypesElse, escapingValueDistTypesElse);
+
+ if (llvm::is_contained(escapingValueDistTypesThen, Type{}) ||
+ llvm::is_contained(escapingValueDistTypesElse, Type{}))
+ return failure();
+
+ // The new `WarpOp` groups yields values in following order:
+ // 1. Escaping values then branch
+ // 2. Escaping values else branch
+ // 3. All non-`ifOp` yielded values.
+ SmallVector<Value> newWarpOpYieldValues{escapingValuesThen.begin(),
+ escapingValuesThen.end()};
+ newWarpOpYieldValues.append(escapingValuesElse.begin(),
+ escapingValuesElse.end());
+ SmallVector<Type> newWarpOpDistTypes = escapingValueDistTypesThen;
+ newWarpOpDistTypes.append(escapingValueDistTypesElse.begin(),
+ escapingValueDistTypesElse.end());
+
+ llvm::SmallDenseMap<unsigned, unsigned> origToNewYieldIdx;
+ for (auto [idx, val] :
+ llvm::zip_equal(nonIfYieldIndices, nonIfYieldValues)) {
+ origToNewYieldIdx[idx] = newWarpOpYieldValues.size();
+ newWarpOpYieldValues.push_back(val);
+ newWarpOpDistTypes.push_back(warpOp.getResult(idx).getType());
+ }
+ // Create the new `WarpOp` with the updated yield values and types.
+ WarpExecuteOnLane0Op newWarpOp = moveRegionToNewWarpOpAndReplaceReturns(
+ rewriter, warpOp, newWarpOpYieldValues, newWarpOpDistTypes);
+
+ // `ifOp` returns the result of the inner warp op.
+ SmallVector<Type> newIfOpDistResTypes;
+ for (auto [i, res] : llvm::enumerate(ifOp.getResults())) {
+ Type distType = cast<Value>(res).getType();
+ if (auto vecType = dyn_cast<VectorType>(distType)) {
+ AffineMap map = distributionMapFn(cast<Value>(res));
+ distType = ifResultDistTypes.count(i)
+ ? ifResultDistTypes[i]
+ : getDistributedType(vecType, map, warpOp.getWarpSize());
+ }
+ newIfOpDistResTypes.push_back(distType);
+ }
+ // Create a new `IfOp` outside the new `WarpOp` region.
+ OpBuilder::InsertionGuard g(rewriter);
+ rewriter.setInsertionPointAfter(newWarpOp);
+ auto newIfOp = scf::IfOp::create(rewriter, ifOp.getLoc(),
+ newIfOpDistResTypes, ifOp.getCondition(),
+ static_cast<bool>(ifOp.thenBlock()),
+ static_cast<bool>(ifOp.elseBlock()));
+
+ auto processBranch = [&](Block *oldIfBranch, Block *newIfBranch,
+ llvm::SmallSetVector<Value, 32> &escapingValues,
+ SmallVector<Type> &escapingValueInputTypes) {
+ OpBuilder::InsertionGuard g(rewriter);
+ if (!newIfBranch)
+ return;
+ rewriter.setInsertionPointToStart(newIfBranch);
+ llvm::SmallDenseMap<Value, int64_t> escapeValToBlockArgIndex;
+ SmallVector<Value> innerWarpInputVals;
+ SmallVector<Type> innerWarpInputTypes;
+ for (size_t i = 0; i < escapingValues.size(); ++i) {
+ innerWarpInputVals.push_back(newWarpOp.getResult(i));
+ escapeValToBlockArgIndex[escapingValues[i]] =
+ innerWarpInputTypes.size();
+ innerWarpInputTypes.push_back(escapingValueInputTypes[i]);
+ }
+ auto innerWarp = WarpExecuteOnLane0Op::create(
+ rewriter, newWarpOp.getLoc(), newIfOp.getResultTypes(),
+ newWarpOp.getLaneid(), newWarpOp.getWarpSize(), innerWarpInputVals,
+ innerWarpInputTypes);
+
+ innerWarp.getWarpRegion().takeBody(*oldIfBranch->getParent());
+ innerWarp.getWarpRegion().addArguments(
+ innerWarpInputTypes,
+ SmallVector<Location>(innerWarpInputTypes.size(), ifOp.getLoc()));
+
+ SmallVector<Value> yieldOperands;
+ for (Value operand : oldIfBranch->getTerminator()->getOperands())
+ yieldOperands.push_back(operand);
+ rewriter.eraseOp(oldIfBranch->getTerminator());
+
+ rewriter.setInsertionPointToEnd(innerWarp.getBody());
+ gpu::YieldOp::create(rewriter, innerWarp.getLoc(), yieldOperands);
+ rewriter.setInsertionPointAfter(innerWarp);
+ scf::YieldOp::create(rewriter, ifOp.getLoc(), innerWarp.getResults());
+
+ // Update any users of escaping values that were forwarded to the
+ // inner `WarpOp`. These values are now arguments of the inner `WarpOp`.
+ innerWarp.walk([&](Operation *op) {
+ for (OpOperand &operand : op->getOpOperands()) {
+ auto it = escapeValToBlockArgIndex.find(operand.get());
+ if (it == escapeValToBlockArgIndex.end())
+ continue;
+ operand.set(innerWarp.getBodyRegion().getArgument(it->second));
+ }
+ });
+ mlir::vector::moveScalarUniformCode(innerWarp);
+ };
+ processBranch(&ifOp.getThenRegion().front(),
+ &newIfOp.getThenRegion().front(), escapingValuesThen,
+ escapingValueInputTypesThen);
+ if (!ifOp.getElseRegion().empty())
+ processBranch(&ifOp.getElseRegion().front(),
+ &newIfOp.getElseRegion().front(), escapingValuesElse,
+ escapingValueInputTypesElse);
+ // Update the users of `<- WarpOp.yield <- IfOp.yield` to use the new `IfOp`
+ // result.
+ for (auto [origIdx, newIdx] : ifResultMapping)
+ rewriter.replaceAllUsesExcept(warpOp.getResult(origIdx),
+ newIfOp.getResult(newIdx), newIfOp);
+ // Similarly, update any users of the `WarpOp` results that were not
+ // results of the `IfOp`.
+ for (auto [origIdx, newIdx] : origToNewYieldIdx)
+ rewriter.replaceAllUsesWith(warpOp.getResult(origIdx),
+ newWarpOp.getResult(newIdx));
+ // Remove the original `WarpOp` and `IfOp`, they should not have any uses
+ // at this point.
+ rewriter.eraseOp(ifOp);
+ rewriter.eraseOp(warpOp);
+ return success();
+ }
+
+private:
+ DistributionMapFn distributionMapFn;
+};
+
/// Sink scf.for region out of WarpExecuteOnLane0Op. This can be done only if
/// the scf.ForOp is the last operation in the region so that it doesn't
/// change the order of execution. This creates a new scf.for region after the
@@ -2068,6 +2267,8 @@ void mlir::vector::populatePropagateWarpVectorDistributionPatterns(
benefit);
patterns.add<WarpOpScfForOp>(patterns.getContext(), distributionMapFn,
benefit);
+ patterns.add<WarpOpScfIfOp>(patterns.getContext(), distributionMapFn,
+ benefit);
}
void mlir::vector::populateDistributeReduction(
diff --git a/mlir/test/Dialect/Vector/vector-warp-distribute.mlir b/mlir/test/Dialect/Vector/vector-warp-distribute.mlir
index 8750582ef1e1f..bb7639204022f 100644
--- a/mlir/test/Dialect/Vector/vector-warp-distribute.mlir
+++ b/mlir/test/Dialect/Vector/vector-warp-distribute.mlir
@@ -1856,3 +1856,72 @@ func.func @negative_warp_step_more_than_warp_size(%laneid: index, %buffer: memre
// CHECK-PROP-LABEL: @negative_warp_step_more_than_warp_size
// CHECK-PROP-NOT: vector.broadcast
// CHECK-PROP: vector.step : vector<64xindex>
+
+// -----
+
+func.func @warp_scf_if_no_yield_distribute(%buffer: memref<128xindex>, %pred : i1) {
+ %laneid = gpu.lane_id
+ %c0 = arith.constant 0 : index
+
+ gpu.warp_execute_on_lane_0(%laneid)[32] {
+ %seq = vector.step : vector<32xindex>
+ scf.if %pred {
+ vector.store %seq, %buffer[%c0] : memref<128xindex>, vector<32xindex>
+ }
+ gpu.yield
+ }
+ return
+}
+
+// CHECK-PROP-LABEL: func.func @warp_scf_if_no_yield_distribute(
+// CHECK-PROP-SAME: %[[ARG0:.+]]: memref<128xindex>, %[[ARG1:.+]]: i1
+// CHECK-PROP: scf.if %[[ARG1]] {
+// CHECK-PROP: gpu.warp_execute_on_lane_0(%{{.*}})[32] args(%{{.*}} : vector<1xindex>) {
+// CHECK-PROP: ^bb0(%[[ARG2:.+]]: vector<32xindex>):
+// CHECK-PROP: vector.store %[[ARG2]], %[[ARG0]][%{{.*}}] : memref<128xindex>, vector<32xindex>
+
+// -----
+
+func.func @warp_scf_if_distribute(%pred : i1) {
+ %laneid = gpu.lane_id
+ %c0 = arith.constant 0 : index
+
+ %0 = gpu.warp_execute_on_lane_0(%laneid)[32] -> vector<1xf32> {
+ %seq1 = vector.step : vector<32xindex>
+ %seq2 = arith.constant dense<2> : vector<32xindex>
+ %0 = scf.if %pred -> (vector<32xf32>) {
+ %1 = "some_op"(%seq1) : (vector<32xindex>) -> (vector<32xf32>)
+ scf.yield %1 : vector<32xf32>
+ } else {
+ %2 = "other_op"(%seq2) : (vector<32xindex>) -> (vector<32xf32>)
+ scf.yield %2 : vector<32xf32>
+ }
+ gpu.yield %0 : vector<32xf32>
+ }
+ "some_use"(%0) : (vector<1xf32>) -> ()
+
+ return
+}
+
+// CHECK-PROP-LABEL: func.func @warp_scf_if_distribute(
+// CHECK-PROP-SAME: %[[ARG0:.+]]: i1
+// CHECK-PROP: %[[SEQ2:.+]] = arith.constant dense<2> : vector<32xindex>
+// CHECK-PROP: %[[LANE_ID:.+]] = gpu.lane_id
+// CHECK-PROP: %[[SEQ1:.+]] = vector.broadcast %[[LANE_ID]] : index to vector<1xindex>
+// CHECK-PROP: %[[IF_YIELD_DIST:.+]] = scf.if %[[ARG0]] -> (vector<1xf32>) {
+// CHECK-PROP: %[[THEN_DIST:.+]] = gpu.warp_execute_on_lane_0(%[[LANE_ID]])[32] args(%[[SEQ1]] : vector<1xindex>) -> (vector<1xf32>) {
+// CHECK-PROP: ^bb0(%[[ARG1:.+]]: vector<32xindex>):
+// CHECK-PROP: %{{.*}} = "some_op"(%[[ARG1]]) : (vector<32xindex>) -> vector<32xf32>
+// CHECK-PROP: gpu.yield %{{.*}} : vector<32xf32>
+// CHECK-PROP: }
+// CHECK-PROP: scf.yield %[[THEN_DIST]] : vector<1xf32>
+// CHECK-PROP: } else {
+// CHECK-PROP: %[[ELSE_DIST:.+]] = gpu.warp_execute_on_lane_0(%[[LANE_ID]])[32] -> (vector<1xf32>) {
+// CHECK-PROP: %{{.*}} = "other_op"(%[[SEQ2]]) : (vector<32xindex>) -> vector<32xf32>
+// CHECK-PROP: gpu.yield %{{.*}} : vector<32xf32>
+// CHECK-PROP: }
+// CHECK-PROP: scf.yield %[[ELSE_DIST]] : vector<1xf32>
+// CHECK-PROP: }
+// CHECK-PROP: "some_use"(%[[IF_YIELD_DIST]]) : (vector<1xf32>) -> ()
+// CHECK-PROP: return
+// CHECK-PROP: }
``````````
</details>
https://github.com/llvm/llvm-project/pull/157119
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