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merged 6 commits into from
Jul 11, 2025

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Meinersbur
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@Meinersbur Meinersbur commented Jul 4, 2025

Support for translating the operations introduced in #144785 to LLVM-IR.

In order to keep the lowering simple, OpenMPIRBuider::unrollLoopHeuristic is applied when encountering the omp.unroll_heuristic op. As a result, the operation that unrolling is applied to (omp.canonical_loop) must have been emitted before even though logically there is no such requirement.

Eventually, all transformations on a loop must be applied directly after emitting omp.canonical_loop, i.e. future transformations must be looked-up when encountering omp.canonical_loop itself. This is because many OpenMPIRBuilder methods (e.g. createParallel) expect all the region code to be emitted withing a callback. In the case of createParallel, the region code is getting outlined into a new function. Therefore, making the operation order a formal requirement would not make the implementation any easier.

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llvmbot commented Jul 7, 2025

@llvm/pr-subscribers-flang-openmp
@llvm/pr-subscribers-mlir-llvm

@llvm/pr-subscribers-mlir

Author: Michael Kruse (Meinersbur)

Changes

Support for translating the operations introduced in #144785 to LLVM-IR.

In order to keep the lowering simple, OpenMPIRBuider::unrollLoopHeuristic is applied when encountering the omp.unroll_heuristic op. As a result, the operation that unrolling is applied to (omp.canonical_loop) must have been emitted before even though logically there is no such requirement.

Eventually, all transformations on a loop must be applied directly after emitting omp.canonical_loop, i.e. future transformations must be looked-up when encountering omp.canonical_loop itself. This is because many OpenMPIRBuilder methods (e.g. createParallel) expect all the region code to be emitted withing a callback. In the case of createParallel, the region code is getting outlined into a new function. Therefore, making the operation requirement an IR order would not make the implementation any easier.


Patch is 21.16 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/147069.diff

6 Files Affected:

  • (modified) mlir/include/mlir/Target/LLVMIR/ModuleTranslation.h (+43)
  • (modified) mlir/lib/Conversion/OpenMPToLLVM/OpenMPToLLVM.cpp (+10)
  • (modified) mlir/lib/Target/LLVMIR/Dialect/OpenMP/OpenMPToLLVMIRTranslation.cpp (+78)
  • (added) mlir/test/Target/LLVMIR/openmp-cli-canonical_loop.mlir (+175)
  • (added) mlir/test/Target/LLVMIR/openmp-cli-unroll-heuristic01.mlir (+56)
  • (added) mlir/test/Target/LLVMIR/openmp-cli-unroll-heuristic02.mlir (+93)
diff --git a/mlir/include/mlir/Target/LLVMIR/ModuleTranslation.h b/mlir/include/mlir/Target/LLVMIR/ModuleTranslation.h
index 79e8bb6add0da..5d52cf3f04b6a 100644
--- a/mlir/include/mlir/Target/LLVMIR/ModuleTranslation.h
+++ b/mlir/include/mlir/Target/LLVMIR/ModuleTranslation.h
@@ -15,6 +15,7 @@
 #define MLIR_TARGET_LLVMIR_MODULETRANSLATION_H
 
 #include "mlir/Dialect/LLVMIR/LLVMInterfaces.h"
+#include "mlir/Dialect/OpenMP/OpenMPDialect.h"
 #include "mlir/IR/Operation.h"
 #include "mlir/IR/SymbolTable.h"
 #include "mlir/IR/Value.h"
@@ -24,6 +25,7 @@
 #include "mlir/Target/LLVMIR/TypeToLLVM.h"
 
 #include "llvm/ADT/SetVector.h"
+#include "llvm/Frontend/OpenMP/OMPIRBuilder.h"
 #include "llvm/IR/FPEnv.h"
 
 namespace llvm {
@@ -108,6 +110,41 @@ class ModuleTranslation {
     return blockMapping.lookup(block);
   }
 
+  /// Find the LLVM-IR loop that represents an MLIR loop.
+  llvm::CanonicalLoopInfo *lookupOMPLoop(omp::NewCliOp mlir) const {
+    llvm::CanonicalLoopInfo *result = loopMapping.lookup(mlir);
+    assert(result && "attempt to get non-existing loop");
+    return result;
+  }
+
+  /// Find the LLVM-IR loop that represents an MLIR loop.
+  llvm::CanonicalLoopInfo *lookupOMPLoop(Value mlir) const {
+    return lookupOMPLoop(mlir.getDefiningOp<omp::NewCliOp>());
+  }
+
+  /// Mark an OpenMP loop as having been consumed.
+  void invalidateOmpLoop(omp::NewCliOp mlir) { loopMapping.erase(mlir); }
+
+  /// Mark an OpenMP loop as having been consumed.
+  void invalidateOmpLoop(Value mlir) {
+    invalidateOmpLoop(mlir.getDefiningOp<omp::NewCliOp>());
+  }
+
+  /// Map an MLIR OpenMP dialect CanonicalLoopInfo to its lowered LLVM-IR
+  /// OpenMPIRBuilder CanonicalLoopInfo
+  void mapOmpLoop(omp::NewCliOp mlir, llvm::CanonicalLoopInfo *llvm) {
+    assert(llvm && "argument must be non-null");
+    llvm::CanonicalLoopInfo *&cur = loopMapping[mlir];
+    assert(cur == nullptr && "attempting to map a loop that is already mapped");
+    cur = llvm;
+  }
+
+  /// Map an MLIR OpenMP dialect CanonicalLoopInfo to its lowered LLVM-IR
+  /// OpenMPIRBuilder CanonicalLoopInfo
+  void mapOmpLoop(Value mlir, llvm::CanonicalLoopInfo *llvm) {
+    mapOmpLoop(mlir.getDefiningOp<omp::NewCliOp>(), llvm);
+  }
+
   /// Stores the mapping between an MLIR operation with successors and a
   /// corresponding LLVM IR instruction.
   void mapBranch(Operation *mlir, llvm::Instruction *llvm) {
@@ -381,6 +418,12 @@ class ModuleTranslation {
   DenseMap<Value, llvm::Value *> valueMapping;
   DenseMap<Block *, llvm::BasicBlock *> blockMapping;
 
+  /// List of not yet consumed MLIR loop handles (represented by an omp.new_cli
+  /// operation which creates a value of type CanonicalLoopInfoType) and their
+  /// LLVM-IR representation as CanonicalLoopInfo which is managed by the
+  /// OpenMPIRBuilder.
+  DenseMap<omp::NewCliOp, llvm::CanonicalLoopInfo *> loopMapping;
+
   /// A mapping between MLIR LLVM dialect terminators and LLVM IR terminators
   /// they are converted to. This allows for connecting PHI nodes to the source
   /// values after all operations are converted.
diff --git a/mlir/lib/Conversion/OpenMPToLLVM/OpenMPToLLVM.cpp b/mlir/lib/Conversion/OpenMPToLLVM/OpenMPToLLVM.cpp
index 77a2708653576..7ac9687c4eeda 100644
--- a/mlir/lib/Conversion/OpenMPToLLVM/OpenMPToLLVM.cpp
+++ b/mlir/lib/Conversion/OpenMPToLLVM/OpenMPToLLVM.cpp
@@ -41,6 +41,16 @@ template <typename T>
 struct OpenMPOpConversion : public ConvertOpToLLVMPattern<T> {
   using ConvertOpToLLVMPattern<T>::ConvertOpToLLVMPattern;
 
+  OpenMPOpConversion(LLVMTypeConverter &typeConverter,
+                     PatternBenefit benefit = 1)
+      : ConvertOpToLLVMPattern<T>(typeConverter, benefit) {
+    // Operations using CanonicalLoopInfoType are lowered only by
+    // mlir::translateModuleToLLVMIR() using the OpenMPIRBuilder. Until then,
+    // the type and operations using it must be preserved.
+    typeConverter.addConversion(
+        [&](::mlir::omp::CanonicalLoopInfoType type) { return type; });
+  }
+
   LogicalResult
   matchAndRewrite(T op, typename T::Adaptor adaptor,
                   ConversionPatternRewriter &rewriter) const override {
diff --git a/mlir/lib/Target/LLVMIR/Dialect/OpenMP/OpenMPToLLVMIRTranslation.cpp b/mlir/lib/Target/LLVMIR/Dialect/OpenMP/OpenMPToLLVMIRTranslation.cpp
index 7a517fb86d1ff..8b9bf7cb2a393 100644
--- a/mlir/lib/Target/LLVMIR/Dialect/OpenMP/OpenMPToLLVMIRTranslation.cpp
+++ b/mlir/lib/Target/LLVMIR/Dialect/OpenMP/OpenMPToLLVMIRTranslation.cpp
@@ -3096,6 +3096,67 @@ convertOmpLoopNest(Operation &opInst, llvm::IRBuilderBase &builder,
   return success();
 }
 
+/// Convert an omp.canonical_loop to LLVM-IR
+static LogicalResult
+convertOmpCanonicalLoopOp(omp::CanonicalLoopOp op, llvm::IRBuilderBase &builder,
+                          LLVM::ModuleTranslation &moduleTranslation) {
+  llvm::OpenMPIRBuilder *ompBuilder = moduleTranslation.getOpenMPBuilder();
+
+  llvm::OpenMPIRBuilder::LocationDescription loopLoc(builder);
+  Value loopIV = op.getInductionVar();
+  Value loopTC = op.getTripCount();
+
+  llvm::Value *llvmTC = moduleTranslation.lookupValue(loopTC);
+
+  llvm::Expected<llvm::CanonicalLoopInfo *> llvmOrError =
+      ompBuilder->createCanonicalLoop(
+          loopLoc,
+          [&](llvm::OpenMPIRBuilder::InsertPointTy ip, llvm::Value *llvmIV) {
+            // Register the mapping of MLIR induction variable to LLVM-IR
+            // induction variable
+            moduleTranslation.mapValue(loopIV, llvmIV);
+
+            builder.restoreIP(ip);
+            llvm::Expected<llvm::BasicBlock *> bodyGenStatus =
+                convertOmpOpRegions(op.getRegion(), "omp.loop.region", builder,
+                                    moduleTranslation);
+
+            return bodyGenStatus.takeError();
+          },
+          llvmTC, "omp.loop");
+  if (!llvmOrError)
+    return op.emitError(llvm::toString(llvmOrError.takeError()));
+
+  llvm::CanonicalLoopInfo *llvmCLI = *llvmOrError;
+  llvm::IRBuilderBase::InsertPoint afterIP = llvmCLI->getAfterIP();
+  builder.restoreIP(afterIP);
+
+  // Register the mapping of MLIR loop to LLVM-IR OpenMPIRBuilder loop
+  if (Value cli = op.getCli())
+    moduleTranslation.mapOmpLoop(cli, llvmCLI);
+
+  return success();
+}
+
+/// Apply a `#pragma omp unroll` / "!$omp unroll" transformation using the
+/// OpenMPIRBuilder.
+static LogicalResult
+applyUnrollHeuristic(omp::UnrollHeuristicOp op, llvm::IRBuilderBase &builder,
+                     LLVM::ModuleTranslation &moduleTranslation) {
+  llvm::OpenMPIRBuilder *ompBuilder = moduleTranslation.getOpenMPBuilder();
+
+  Value applyee = op.getApplyee();
+  assert(applyee && "Loop to apply unrolling on required");
+
+  llvm::CanonicalLoopInfo *consBuilderCLI =
+      moduleTranslation.lookupOMPLoop(applyee);
+  llvm::OpenMPIRBuilder::LocationDescription loc(builder);
+  ompBuilder->unrollLoopHeuristic(loc.DL, consBuilderCLI);
+
+  moduleTranslation.invalidateOmpLoop(applyee);
+  return success();
+}
+
 /// Convert an Atomic Ordering attribute to llvm::AtomicOrdering.
 static llvm::AtomicOrdering
 convertAtomicOrdering(std::optional<omp::ClauseMemoryOrderKind> ao) {
@@ -5988,6 +6049,23 @@ convertHostOrTargetOperation(Operation *op, llvm::IRBuilderBase &builder,
                 // etc. and then discarded
                 return success();
               })
+          .Case([&](omp::NewCliOp op) {
+            // Meta-operation: Doesn't do anything by itself, but used to
+            // identify a loop.
+            return success();
+          })
+          .Case([&](omp::CanonicalLoopOp op) {
+            return convertOmpCanonicalLoopOp(op, builder, moduleTranslation);
+          })
+          .Case([&](omp::UnrollHeuristicOp op) {
+            // FIXME: Handling omp.unroll_heuristic as an executable requires
+            // that the generator (e.g. omp.canonical_loop) has been seen first.
+            // For construct that require all codegen to occur inside a callback
+            // (e.g. OpenMPIRBilder::createParallel), all codegen of that
+            // contained region including their transformations must occur at
+            // the omp.canonical_loop.
+            return applyUnrollHeuristic(op, builder, moduleTranslation);
+          })
           .Default([&](Operation *inst) {
             return inst->emitError()
                    << "not yet implemented: " << inst->getName();
diff --git a/mlir/test/Target/LLVMIR/openmp-cli-canonical_loop.mlir b/mlir/test/Target/LLVMIR/openmp-cli-canonical_loop.mlir
new file mode 100644
index 0000000000000..9abef003d6183
--- /dev/null
+++ b/mlir/test/Target/LLVMIR/openmp-cli-canonical_loop.mlir
@@ -0,0 +1,175 @@
+// Test lowering of standalone omp.canonical_loop
+// RUN: mlir-translate -mlir-to-llvmir %s | FileCheck %s
+
+// CHECK-LABEL: define void @anon_loop(
+// CHECK-SAME:    ptr %[[ptr:.+]],
+// CHECK-SAME:    i32 %[[tc:.+]]) {
+// CHECK-NEXT:    br label %omp_omp.loop.preheader
+// CHECK-EMPTY:
+// CHECK-NEXT:  omp_omp.loop.preheader:
+// CHECK-NEXT:    br label %omp_omp.loop.header
+// CHECK-EMPTY:
+// CHECK-NEXT:  omp_omp.loop.header:
+// CHECK-NEXT:    %omp_omp.loop.iv = phi i32 [ 0, %omp_omp.loop.preheader ], [ %omp_omp.loop.next, %omp_omp.loop.inc ]
+// CHECK-NEXT:    br label %omp_omp.loop.cond
+// CHECK-EMPTY:
+// CHECK-NEXT:  omp_omp.loop.cond:
+// CHECK-NEXT:    %omp_omp.loop.cmp = icmp ult i32 %omp_omp.loop.iv, %[[tc]]
+// CHECK-NEXT:    br i1 %omp_omp.loop.cmp, label %omp_omp.loop.body, label %omp_omp.loop.exit
+// CHECK-EMPTY:
+// CHECK-NEXT:  omp_omp.loop.body:
+// CHECK-NEXT:    br label %omp.loop.region
+// CHECK-EMPTY:
+// CHECK-NEXT:  omp.loop.region:
+// CHECK-NEXT:    store float 4.200000e+01, ptr %[[ptr]], align 4
+// CHECK-NEXT:    br label %omp.region.cont
+// CHECK-EMPTY:
+// CHECK-NEXT:  omp.region.cont:
+// CHECK-NEXT:    br label %omp_omp.loop.inc
+// CHECK-EMPTY:
+// CHECK-NEXT:  omp_omp.loop.inc:
+// CHECK-NEXT:    %omp_omp.loop.next = add nuw i32 %omp_omp.loop.iv, 1
+// CHECK-NEXT:    br label %omp_omp.loop.header
+// CHECK-EMPTY:
+// CHECK-NEXT:  omp_omp.loop.exit:
+// CHECK-NEXT:    br label %omp_omp.loop.after
+// CHECK-EMPTY:
+// CHECK-NEXT:  omp_omp.loop.after:
+// CHECK-NEXT:    ret void
+// CHECK-NEXT:  }
+llvm.func @anon_loop(%ptr: !llvm.ptr, %tc : i32) -> () {
+  omp.canonical_loop %iv : i32 in range(%tc) {
+    %val = llvm.mlir.constant(42.0 : f32) : f32
+    llvm.store %val, %ptr : f32, !llvm.ptr
+    omp.terminator
+  }
+  llvm.return
+}
+
+
+
+// CHECK-LABEL: define void @trivial_loop(
+// CHECK-SAME:    ptr %[[ptr:.+]],
+// CHECK-SAME:    i32 %[[tc:.+]]) {
+// CHECK-NEXT:    br label %omp_omp.loop.preheader
+// CHECK-EMPTY:
+// CHECK-NEXT:  omp_omp.loop.preheader:
+// CHECK-NEXT:    br label %omp_omp.loop.header
+// CHECK-EMPTY:
+// CHECK-NEXT:  omp_omp.loop.header:
+// CHECK-NEXT:    %omp_omp.loop.iv = phi i32 [ 0, %omp_omp.loop.preheader ], [ %omp_omp.loop.next, %omp_omp.loop.inc ]
+// CHECK-NEXT:    br label %omp_omp.loop.cond
+// CHECK-EMPTY:
+// CHECK-NEXT:  omp_omp.loop.cond:
+// CHECK-NEXT:    %omp_omp.loop.cmp = icmp ult i32 %omp_omp.loop.iv, %[[tc]]
+// CHECK-NEXT:    br i1 %omp_omp.loop.cmp, label %omp_omp.loop.body, label %omp_omp.loop.exit
+// CHECK-EMPTY:
+// CHECK-NEXT:  omp_omp.loop.body:
+// CHECK-NEXT:    br label %omp.loop.region
+// CHECK-EMPTY:
+// CHECK-NEXT:  omp.loop.region:
+// CHECK-NEXT:    store float 4.200000e+01, ptr %[[ptr]], align 4
+// CHECK-NEXT:    br label %omp.region.cont
+// CHECK-EMPTY:
+// CHECK-NEXT:  omp.region.cont:
+// CHECK-NEXT:    br label %omp_omp.loop.inc
+// CHECK-EMPTY:
+// CHECK-NEXT:  omp_omp.loop.inc:
+// CHECK-NEXT:    %omp_omp.loop.next = add nuw i32 %omp_omp.loop.iv, 1
+// CHECK-NEXT:    br label %omp_omp.loop.header
+// CHECK-EMPTY:
+// CHECK-NEXT:  omp_omp.loop.exit:
+// CHECK-NEXT:    br label %omp_omp.loop.after
+// CHECK-EMPTY:
+// CHECK-NEXT:  omp_omp.loop.after:
+// CHECK-NEXT:    ret void
+// CHECK-NEXT:  }
+llvm.func @trivial_loop(%ptr: !llvm.ptr, %tc : i32) -> () {
+  %cli = omp.new_cli
+  omp.canonical_loop(%cli) %iv : i32 in range(%tc) {
+    %val = llvm.mlir.constant(42.0 : f32) : f32
+    llvm.store %val, %ptr : f32, !llvm.ptr
+    omp.terminator
+  }
+  llvm.return
+}
+
+
+// CHECK-LABEL: define void @nested_loop(
+// CHECK-SAME:    ptr %[[ptr:.+]], i32 %[[outer_tc:.+]], i32 %[[inner_tc:.+]]) {
+// CHECK-NEXT:  br label %omp_omp.loop.preheader
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.preheader:
+// CHECK-NEXT:  br label %omp_omp.loop.header
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.header:
+// CHECK-NEXT:  %omp_omp.loop.iv = phi i32 [ 0, %omp_omp.loop.preheader ], [ %omp_omp.loop.next, %omp_omp.loop.inc ]
+// CHECK-NEXT:  br label %omp_omp.loop.cond
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.cond:
+// CHECK-NEXT:  %omp_omp.loop.cmp = icmp ult i32 %omp_omp.loop.iv, %[[outer_tc]]
+// CHECK-NEXT:  br i1 %omp_omp.loop.cmp, label %omp_omp.loop.body, label %omp_omp.loop.exit
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.body:
+// CHECK-NEXT:  br label %omp.loop.region
+// CHECK-EMPTY:
+// CHECK-NEXT: omp.loop.region:
+// CHECK-NEXT:  br label %omp_omp.loop.preheader1
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.preheader1:
+// CHECK-NEXT:  br label %omp_omp.loop.header2
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.header2:
+// CHECK-NEXT:  %omp_omp.loop.iv8 = phi i32 [ 0, %omp_omp.loop.preheader1 ], [ %omp_omp.loop.next10, %omp_omp.loop.inc5 ]
+// CHECK-NEXT:  br label %omp_omp.loop.cond3
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.cond3:
+// CHECK-NEXT:  %omp_omp.loop.cmp9 = icmp ult i32 %omp_omp.loop.iv8, %[[inner_tc]]
+// CHECK-NEXT:  br i1 %omp_omp.loop.cmp9, label %omp_omp.loop.body4, label %omp_omp.loop.exit6
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.body4:
+// CHECK-NEXT:  br label %omp.loop.region12
+// CHECK-EMPTY:
+// CHECK-NEXT: omp.loop.region12:
+// CHECK-NEXT:  store float 4.200000e+01, ptr %[[ptr]], align 4
+// CHECK-NEXT:  br label %omp.region.cont11
+// CHECK-EMPTY:
+// CHECK-NEXT: omp.region.cont11:
+// CHECK-NEXT:  br label %omp_omp.loop.inc5
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.inc5:
+// CHECK-NEXT:  %omp_omp.loop.next10 = add nuw i32 %omp_omp.loop.iv8, 1
+// CHECK-NEXT:  br label %omp_omp.loop.header2
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.exit6:
+// CHECK-NEXT:  br label %omp_omp.loop.after7
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.after7:
+// CHECK-NEXT:  br label %omp.region.cont
+// CHECK-EMPTY:
+// CHECK-NEXT: omp.region.cont:
+// CHECK-NEXT:  br label %omp_omp.loop.inc
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.inc:
+// CHECK-NEXT:  %omp_omp.loop.next = add nuw i32 %omp_omp.loop.iv, 1
+// CHECK-NEXT:  br label %omp_omp.loop.header
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.exit:
+// CHECK-NEXT:  br label %omp_omp.loop.after
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.after:
+// CHECK-NEXT:  ret void
+// CHECK-NEXT: }
+llvm.func @nested_loop(%ptr: !llvm.ptr, %outer_tc : i32, %inner_tc : i32) -> () {
+  %outer_cli = omp.new_cli
+  %inner_cli = omp.new_cli
+  omp.canonical_loop(%outer_cli) %outer_iv : i32 in range(%outer_tc) {
+    omp.canonical_loop(%inner_cli) %inner_iv : i32 in range(%inner_tc) {
+      %val = llvm.mlir.constant(42.0 : f32) : f32
+      llvm.store %val, %ptr : f32, !llvm.ptr
+      omp.terminator
+    }
+    omp.terminator
+  }
+  llvm.return
+}
diff --git a/mlir/test/Target/LLVMIR/openmp-cli-unroll-heuristic01.mlir b/mlir/test/Target/LLVMIR/openmp-cli-unroll-heuristic01.mlir
new file mode 100644
index 0000000000000..0f0448e15f983
--- /dev/null
+++ b/mlir/test/Target/LLVMIR/openmp-cli-unroll-heuristic01.mlir
@@ -0,0 +1,56 @@
+// Test lowering of the omp.unroll_heuristic
+// RUN: mlir-translate -mlir-to-llvmir %s | FileCheck %s
+
+
+// CHECK-LABEL: define void @unroll_heuristic_trivial_loop(
+// CHECK-SAME:    ptr %[[ptr:.+]], i32 %[[tc:.+]]) {
+// CHECK-NEXT:   br label %omp_omp.loop.preheader
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.preheader:
+// CHECK-NEXT:   br label %omp_omp.loop.header
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.header:
+// CHECK-NEXT:   %omp_omp.loop.iv = phi i32 [ 0, %omp_omp.loop.preheader ], [ %omp_omp.loop.next, %omp_omp.loop.inc ]
+// CHECK-NEXT:   br label %omp_omp.loop.cond
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.cond:
+// CHECK-NEXT:   %omp_omp.loop.cmp = icmp ult i32 %omp_omp.loop.iv, %[[tc]]
+// CHECK-NEXT:   br i1 %omp_omp.loop.cmp, label %omp_omp.loop.body, label %omp_omp.loop.exit
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.body:
+// CHECK-NEXT:   br label %omp.loop.region
+// CHECK-EMPTY:
+// CHECK-NEXT: omp.loop.region:
+// CHECK-NEXT:   store float 4.200000e+01, ptr %[[ptr]], align 4
+// CHECK-NEXT:   br label %omp.region.cont
+// CHECK-EMPTY:
+// CHECK-NEXT: omp.region.cont:
+// CHECK-NEXT:   br label %omp_omp.loop.inc
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.inc:
+// CHECK-NEXT:   %omp_omp.loop.next = add nuw i32 %omp_omp.loop.iv, 1
+// CHECK-NEXT:   br label %omp_omp.loop.header, !llvm.loop ![[$MD1:[0-9]+]]
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.exit:
+// CHECK-NEXT:   br label %omp_omp.loop.after
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.after:
+// CHECK-NEXT:   ret void
+// CHECK-NEXT: }
+llvm.func @unroll_heuristic_trivial_loop(%ptr: !llvm.ptr, %tc: i32) -> () {
+  %literal_cli = omp.new_cli
+  omp.canonical_loop(%literal_cli) %iv : i32 in range(%tc) {
+    %val = llvm.mlir.constant(42.0 : f32) : f32
+    llvm.store %val, %ptr : f32, !llvm.ptr
+    omp.terminator
+  }
+  omp.unroll_heuristic(%literal_cli)
+  llvm.return
+}
+
+
+// Start of metadata
+// CHECK-LABEL: !llvm.module.flags
+
+// CHECK: ![[$MD1]] = distinct !{![[$MD1]], ![[$MD2:[0-9]+]]}
+// CHECK: ![[$MD2]] = !{!"llvm.loop.unroll.enable"}
diff --git a/mlir/test/Target/LLVMIR/openmp-cli-unroll-heuristic02.mlir b/mlir/test/Target/LLVMIR/openmp-cli-unroll-heuristic02.mlir
new file mode 100644
index 0000000000000..f82b4990e378e
--- /dev/null
+++ b/mlir/test/Target/LLVMIR/openmp-cli-unroll-heuristic02.mlir
@@ -0,0 +1,93 @@
+// Test lowering of the omp.unroll_heuristic
+// RUN: mlir-translate -mlir-to-llvmir %s | FileCheck %s
+
+
+// CHECK-LABEL: define void @unroll_heuristic_nested_loop(
+// CHECK-SAME:    ptr %[[ptr:.+]], i32 %[[outer_tc:.+]], i32 %[[inner_tc:.+]]) {
+// CHECK-NEXT:   br label %omp_omp.loop.preheader
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.preheader:
+// CHECK-NEXT:   br label %omp_omp.loop.header
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.header:
+// CHECK-NEXT:   %omp_omp.loop.iv = phi i32 [ 0, %omp_omp.loop.preheader ], [ %omp_omp.loop.next, %omp_omp.loop.inc ]
+// CHECK-NEXT:   br label %omp_omp.loop.cond
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.cond:
+// CHECK-NEXT:   %omp_omp.loop.cmp = icmp ult i32 %omp_omp.loop.iv, %[[outer_tc]]
+// CHECK-NEXT:   br i1 %omp_omp.loop.cmp, label %omp_omp.loop.body, label %omp_omp.loop.exit
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.body:
+// CHECK-NEXT:   br label %omp.loop.region
+// CHECK-EMPTY:
+// CHECK-NEXT: omp.loop.region:
+// CHECK-NEXT:   br label %omp_omp.loop.preheader1
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.preheader1:
+// CHECK-NEXT:   br label %omp_omp.loop.header2
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.header2:
+// CHECK-NEXT:   %omp_omp.loop.iv8 = phi i32 [ 0, %omp_omp.loop.preheader1 ], [ %omp_omp.loop.next10, %omp_omp.loop.inc5 ]
+// CHECK-NEXT:   br label %omp_omp.loop.cond3
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.cond3:
+// CHECK-NEXT:   %omp_omp.loop.cmp9 = icmp ult i32 %omp_omp.loop.iv8, %[[inner_tc]]
+// CHECK-NEXT:   br i1 %omp_omp.loop.cmp9, label %omp_omp.loop.body4, label %omp_omp.loop.exit6
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.body4:
+// CHECK-NEXT:   br label %omp.loop.region12
+// CHECK-EMPTY:
+// CHECK-NEXT: omp.loop.region12:
+// CHECK-NEXT:   store float 4.200000e+01, ptr %[[ptr]], align 4
+// CHECK-NEXT:   br label %omp.region.cont11
+// CHECK-EMPTY:
+// CHECK-NEXT: omp.region.cont11:
+// CHECK-NEXT:   br label %omp_omp.loop.inc5
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.inc5:
+// CHECK-NEXT:   %omp_omp.loop.next10 = add nuw i32 %omp_omp.loop.iv8, 1
+// CHECK-NEXT:   br label %omp_omp.loop.header2, !llvm.loop ![[$MD1:[0-9]+]]
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.exit6:
+// CHECK-NEXT:   br label %omp_omp.loop.after7
+// CHECK-EMPTY:
+// CHECK-NEXT: omp_omp.loop.after7:
+// CHECK-NEXT:   br label %omp.region.cont
+// CHECK-EMPTY:
+// CHECK-NEXT: omp.region.cont:
+// CHECK-NEXT:   br label %...
[truncated]

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LGTM. Thanks for splitting the PR. Please wait for another approval before merging.

Base automatically changed from users/meinersbur/flang_canonical-loop_ops to main July 10, 2025 10:53
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LGTM, thanks!

@Meinersbur Meinersbur merged commit 96bc07d into main Jul 11, 2025
9 checks passed
@Meinersbur Meinersbur deleted the users/meinersbur/flang_canonical-loop_ops-lowering branch July 11, 2025 10:54
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fabrizio-indirli commented Jul 24, 2025

Hi all, in our downstream project we build the libMLIRLLVMIRTransforms target separately (e.g. with ninja libMLIRLLVMIRTransforms.a ).
After this commit (96bc07d49221dc40eb751e0759be2ccbb8a64f00), we're not able to build it anymore because it fails with the error:

[1629/1745] Building CXX object tools/mlir/lib/Dial...eFiles/obj.MLIRNVVMDialect.dir/IR/NVVMDialect.cpp.o
FAILED: tools/mlir/lib/Dialect/LLVMIR/CMakeFiles/obj.MLIRNVVMDialect.dir/IR/NVVMDialect.cpp.o
/usr/bin/g++-11 -DEXPERIMENTAL_KEY_INSTRUCTIONS -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -Illvm-project/build/tools/mlir/lib/Dialect/LLVMIR -Illvm-project/mlir/lib/Dialect/LLVMIR -Illvm-project/build/tools/mlir/include -Illvm-project/mlir/include -Illvm-project/build/include -Illvm-project/llvm/include -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough -Wno-uninitialized -Wno-nonnull -Wno-class-memaccess -Wno-redundant-move -Wno-pessimizing-move -Wno-noexcept-type -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -Wno-misleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -Wundef -Wno-unused-but-set-parameter -Wno-deprecated-copy -O3 -DNDEBUG -std=c++17 -MD -MT tools/mlir/lib/Dialect/LLVMIR/CMakeFiles/obj.MLIRNVVMDialect.dir/IR/NVVMDialect.cpp.o -MF tools/mlir/lib/Dialect/LLVMIR/CMakeFiles/obj.MLIRNVVMDialect.dir/IR/NVVMDialect.cpp.o.d -o tools/mlir/lib/Dialect/LLVMIR/CMakeFiles/obj.MLIRNVVMDialect.dir/IR/NVVMDialect.cpp.o -c llvm-project/mlir/lib/Dialect/LLVMIR/IR/NVVMDialect.cpp
In file included from llvm-project/llvm/include/llvm/Frontend/OpenMP/OMPConstants.h:19,
from llvm-project/llvm/include/llvm/Frontend/OpenMP/OMPIRBuilder.h:18,
from llvm-project/mlir/include/mlir/Target/LLVMIR/ModuleTranslation.h:28,
from llvm-project/mlir/include/mlir/Dialect/LLVMIR/NVVMDialect.h:26,
from llvm-project/mlir/lib/Dialect/LLVMIR/IR/NVVMDialect.cpp:17:
llvm-project/llvm/include/llvm/Frontend/OpenMP/OMP.h:16:10: fatal error: llvm/Frontend/OpenMP/OMP.h.inc: No such file or directory
16 | #include "llvm/Frontend/OpenMP/OMP.h.inc"
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.

We configure the build with the following CMake command:

cmake -G Ninja -S llvm -B build -DLLVM_ENABLE_PROJECTS=mlir -DCMAKE_BUILD_TYPE=Release -DLLVM_TARGETS_TO_BUILD=X86 -DLLVM_REQUIRES_RTTI=ON -DLLVM_REQUIRES_EH=ON -DLLVM_ENABLE_ASSERTIONS=0 -DLLVM_ABI_BREAKING_CHECKS=FORCE_OFF -DLLVM_ENABLE_TERMINFO=OFF -DLLVM_USE_LINKER=lld

using GCC v11.4 and CMake v3.31 on Ubuntu 24.04. This issue shows when doing a clean build in Release mode.

For reference, this quick-and-dirty fix seems to allow the target to be built:

--- a/mlir/lib/Dialect/LLVMIR/Transforms/CMakeLists.txt
+++ b/mlir/lib/Dialect/LLVMIR/Transforms/CMakeLists.txt
@@ -9,6 +9,7 @@ add_mlir_dialect_library(MLIRLLVMIRTransforms
   RequestCWrappers.cpp
 
   DEPENDS
+  omp_gen
   MLIRLLVMPassIncGen
 
   LINK_LIBS PUBLIC

although we probably shouldn't do this as MLIRLLVMIRTransforms doesn't depend directly on OpenMP headers, if I understand correctly.

@Meinersbur is it expected that mlir/include/mlir/Target/LLVMIR/ModuleTranslation.h now includes OpenMP specific code, given that the remainder of the header seems to be mostly on LLVM IR? If so, could there be a missing dependency in some CMakeLists file?

Thank you in advance :)

@Meinersbur
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Meinersbur commented Jul 30, 2025

@Meinersbur is it expected that mlir/include/mlir/Target/LLVMIR/ModuleTranslation.h now includes OpenMP specific code, given that the remainder of the header seems to be mostly on LLVM IR? If so, could there be a missing dependency in some CMakeLists file?

ModuleTranslation.h always included OpenMP-specific code in form of getOpenMPBuilder(). This is because instead of translating the OpenMP Dialect to the LLVM Dialect, the LLVM and OpenMP Dialect are translated together to LLVM-IR. This was a comprimise reached in the past in order to reuse the OpenMPIRBuilder. The header is affected now because the loopMapping field is needed to remember the mapping between OpenMP Dialect operations and OpenMPIRBuilder objects.

The only thing that changed is that previously OpenMPIRBuilder was only forward-declared instead if including the header. I think was only a means of reducing the number of included files, not to a guarantee that there is not dependence.

I will add the additional dependency.

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Meinersbur commented Jul 30, 2025

Turns out only CanonicalLoopInfo needs to be also forward-declared. Although I still think there logically is a dependency of MLIRLLVMIRTransforms on the OpenMPBuilder (it is still, and long-time has been, used in ModuleTranslation.cpp), we also want to use include-what-you-use-style forward declarations in the header.

Applied here: #151302

Meinersbur added a commit that referenced this pull request Jul 30, 2025
`#include "llvm/Frontend/OpenMP/OMPIRBuilder.h"` can be replaced with
forward-declarations of `OpenMPIRBuilder` and `CanonicalLoopInfo`. This
also avoids a dependency to `omp_gen` of the LLVMFrontendOpenMP
component which is included indirectly in `OMPIRBuilder.h`.

Since its inclusion in #147069, additional indirect dependencies on
headers included by `OMPIRBuilder.h` were introduced as well. These are
now included directly.

Reported-by: fabrizio-indirli

See
#147069 (comment)
llvm-sync bot pushed a commit to arm/arm-toolchain that referenced this pull request Jul 30, 2025
`#include "llvm/Frontend/OpenMP/OMPIRBuilder.h"` can be replaced with
forward-declarations of `OpenMPIRBuilder` and `CanonicalLoopInfo`. This
also avoids a dependency to `omp_gen` of the LLVMFrontendOpenMP
component which is included indirectly in `OMPIRBuilder.h`.

Since its inclusion in #147069, additional indirect dependencies on
headers included by `OMPIRBuilder.h` were introduced as well. These are
now included directly.

Reported-by: fabrizio-indirli

See
llvm/llvm-project#147069 (comment)
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5 participants