[Codegen] Add pass to verify workgroup distribution (#19186)

While general verification is not possible, when using `scf.forall` for
workgroup distribution we have the opportunity for basic verification
that all writes are located within the distributed loop. In particular,
if we have any workgroup level loops, any write to global memory outside
is assumed to be illegal.

This happens after bufferization because it is impossible to do this
verification before determining the memory space of every tensor in the
dispatch.

This pass is relatively lightweight (two walks, both of which should be
short) and so is on by default for every CPU and GPU pipeline.

Author: qedawkins

compiler/src/iree/compiler/Codegen/Common/BUILD.bazel

@@ -154,6 +154,7 @@ iree_compiler_cc_library(
         "UnrollAnnotatedLoops.cpp",
         "UserConfig.cpp",
         "VectorizeMemrefCopy.cpp",
+        "VerifyWorkgroupDistribution.cpp",
     ],
     hdrs = [
         "BufferizationAnalysis.h",

compiler/src/iree/compiler/Codegen/Common/CMakeLists.txt

@@ -146,6 +146,7 @@ iree_cc_library(
     "UnrollAnnotatedLoops.cpp"
     "UserConfig.cpp"
     "VectorizeMemrefCopy.cpp"
+    "VerifyWorkgroupDistribution.cpp"
   DEPS
     ::PassHeaders
     ::PassesIncGen

compiler/src/iree/compiler/Codegen/Common/Passes.td

@@ -633,4 +633,15 @@ def VectorizeMemrefCopyPass :
   let summary = "Vectorizes memref copy operations.";
 }
 
+def VerifyWorkgroupDistributionPass :
+    InterfacePass<"iree-codegen-verify-workgroup-distribution", "mlir::FunctionOpInterface"> {
+  let summary = "Pass to verify proper distribution to workgroups.";
+  let description = [{
+    Pass to verify that all writes to global memory are explicitly mapped to
+    workgroups. This means that in cases where we use loops (scf.forall) to
+    manage distribution to workgroups, we require that all ops with write
+    side effects are contained within a workgroup distributed loop.
+  }];
+}
+
 #endif // IREE_CODEGEN_COMMON_PASSES

compiler/src/iree/compiler/Codegen/Common/VerifyWorkgroupDistribution.cpp

@@ -0,0 +1,89 @@
+// Copyright 2024 The IREE Authors
+//
+// Licensed under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include "iree/compiler/Codegen/Common/Passes.h"
+#include "iree/compiler/Codegen/Dialect/Codegen/IR/IREECodegenAttrs.h"
+#include "iree/compiler/Codegen/Utils/GPUUtils.h"
+#include "iree/compiler/Dialect/HAL/IR/HALTypes.h"
+#include "mlir/IR/Visitors.h"
+#include "mlir/Interfaces/FunctionInterfaces.h"
+#include "mlir/Interfaces/SideEffectInterfaces.h"
+
+namespace mlir::iree_compiler {
+
+#define GEN_PASS_DEF_VERIFYWORKGROUPDISTRIBUTIONPASS
+#include "iree/compiler/Codegen/Common/Passes.h.inc"
+
+namespace {
+
+struct VerifyWorkgroupDistributionPass final
+    : impl::VerifyWorkgroupDistributionPassBase<
+          VerifyWorkgroupDistributionPass> {
+
+  void runOnOperation() override {
+    FunctionOpInterface funcOp = getOperation();
+
+    WalkResult hasForall = funcOp.walk([&](scf::ForallOp forallOp) {
+      if (forallOpHasMappingType<IREE::Codegen::WorkgroupMappingAttr>(
+              forallOp)) {
+        return WalkResult::interrupt();
+      }
+      return WalkResult::advance();
+    });
+
+    // Without a workgroup level forall, either this is a single workgroup
+    // dispatch, in which case no verification is needed, or this is already
+    // distributed in which case verification is no longer possible.
+    if (!hasForall.wasInterrupted()) {
+      return;
+    }
+
+    auto globalAddressSpace = IREE::HAL::DescriptorTypeAttr::get(
+        &getContext(), IREE::HAL::DescriptorType::StorageBuffer);
+
+    // Walk in PreOrder so that parent operations are visited before children,
+    // thus allowing all operations contained within workgroup foralls to be
+    // skipped.
+    WalkResult res = funcOp.walk<WalkOrder::PreOrder>([&](Operation *op) {
+      if (auto forallOp = dyn_cast<scf::ForallOp>(op)) {
+        // Skip ops contained within forall ops with workgroup mappings.
+        if (forallOpHasMappingType<IREE::Codegen::WorkgroupMappingAttr>(
+                forallOp)) {
+          return WalkResult::skip();
+        }
+      }
+      if (auto memoryEffectOp = dyn_cast<MemoryEffectOpInterface>(op)) {
+        for (Value operand : memoryEffectOp->getOperands()) {
+          auto type = dyn_cast<MemRefType>(operand.getType());
+          if (!type ||
+              !memoryEffectOp.getEffectOnValue<MemoryEffects::Write>(operand)) {
+            continue;
+          }
+
+          // Writes to non-global memory are fine.
+          if (type.getMemorySpace() != globalAddressSpace) {
+            continue;
+          }
+
+          op->emitOpError(
+              "write affecting operations on global resources are restricted "
+              "to workgroup distributed contexts.");
+          return WalkResult::interrupt();
+        }
+      }
+      return WalkResult::advance();
+    });
+
+    if (res.wasInterrupted()) {
+      funcOp.emitOpError("failed on workgroup distribution verification");
+      return signalPassFailure();
+    }
+  }
+};
+
+} // namespace
+
+} // namespace mlir::iree_compiler

compiler/src/iree/compiler/Codegen/Common/test/BUILD.bazel

@@ -86,6 +86,7 @@ iree_lit_test_suite(
             "vectorize_memref_copy.mlir",
             "vectorize_tensor_pad.mlir",
             "vector_layout_analysis.mlir",
+            "verify_workgroup_distribution.mlir",
         ],
         include = ["*.mlir"],
         exclude = [

compiler/src/iree/compiler/Codegen/Common/test/CMakeLists.txt

@@ -82,6 +82,7 @@ iree_lit_test_suite(
     "vector_layout_analysis.mlir"
     "vectorize_memref_copy.mlir"
     "vectorize_tensor_pad.mlir"
+    "verify_workgroup_distribution.mlir"
   TOOLS
     FileCheck
     iree-opt

compiler/src/iree/compiler/Codegen/Common/test/verify_workgroup_distribution.mlir

@@ -0,0 +1,40 @@
+// RUN: iree-opt %s --split-input-file --verify-diagnostics \
+// RUN:   --pass-pipeline="builtin.module(func.func(iree-codegen-verify-workgroup-distribution))" \
+// RUN:   | FileCheck %s
+
+// expected-error@+1 {{op failed on workgroup distribution verification}}
+func.func @write_outside_workgroup_forall(%i: i32, %out: memref<32xi32, #hal.descriptor_type<storage_buffer>>) {
+  scf.forall (%arg0) in (32) {
+  } {mapping = [#iree_codegen.workgroup_mapping<x>]}
+  %c0 = arith.constant 0 : index
+  // expected-error@+1 {{write affecting operations on global resources are restricted to workgroup distributed contexts.}}
+  memref.store %i, %out[%c0] : memref<32xi32, #hal.descriptor_type<storage_buffer>>
+  return
+}
+
+// -----
+
+// CHECK: func @non_workgroup_write_outside_workgroup_forall
+func.func @non_workgroup_write_outside_workgroup_forall(
+  %i: i32, %out: memref<32xi32, #hal.descriptor_type<storage_buffer>>, %out2: memref<32xi32>) {
+  scf.forall (%arg0) in (32) {
+    memref.store %i, %out[%arg0] : memref<32xi32, #hal.descriptor_type<storage_buffer>>
+  } {mapping = [#iree_codegen.workgroup_mapping<x>]}
+  %c0 = arith.constant 0 : index
+  memref.store %i, %out2[%c0] : memref<32xi32>
+  return
+}
+
+// -----
+
+// expected-error@+1 {{op failed on workgroup distribution verification}}
+func.func @write_nested_in_other_forall(%i: i32, %out: memref<32xi32, #hal.descriptor_type<storage_buffer>>) {
+  scf.forall (%arg0) in (32) {
+  } {mapping = [#iree_codegen.workgroup_mapping<x>]}
+  %c0 = arith.constant 0 : index
+  scf.forall (%arg1) in (32) {
+    // expected-error@+1 {{write affecting operations on global resources are restricted to workgroup distributed contexts.}}
+    memref.store %i, %out[%arg1] : memref<32xi32, #hal.descriptor_type<storage_buffer>>
+  }
+  return
+}

compiler/src/iree/compiler/Codegen/LLVMCPU/Passes.cpp

@@ -813,7 +813,8 @@ void buildLLVMCPUCodegenPassPipeline(OpPassManager &variantPassManager,
     OpPassManager &modulePassManager = variantPassManager.nest<ModuleOp>();
     modulePassManager.addPass(createLowerExecutableUsingTransformDialectPass());
     FunctionLikeNest(modulePassManager)
-        .addPass(createLLVMCPULowerExecutableTargetPass);
+        .addPass(createLLVMCPULowerExecutableTargetPass)
+        .addPass(createVerifyWorkgroupDistributionPass);
   }
 
   variantPassManager.addPass(createReconcileTranslationInfoPass());

compiler/src/iree/compiler/Codegen/LLVMGPU/Passes.cpp

@@ -1184,7 +1184,8 @@ void buildLLVMGPUCodegenPassPipeline(OpPassManager &variantPassManager,
     OpPassManager &modulePassManager = variantPassManager.nest<ModuleOp>();
     modulePassManager.addPass(createLowerExecutableUsingTransformDialectPass());
     FunctionLikeNest(modulePassManager)
-        .addPass(createLLVMGPULowerExecutableTargetPass);
+        .addPass(createLLVMGPULowerExecutableTargetPass)
+        .addPass(createVerifyWorkgroupDistributionPass);
   }
   variantPassManager.addPass(createReconcileTranslationInfoPass());
 
@@ -1250,7 +1251,8 @@ void buildROCDLCodegenPassPipeline(OpPassManager &variantPassManager) {
     OpPassManager &modulePassManager = variantPassManager.nest<ModuleOp>();
     modulePassManager.addPass(createLowerExecutableUsingTransformDialectPass());
     FunctionLikeNest(modulePassManager)
-        .addPass(createROCDLLowerExecutableTargetPass);
+        .addPass(createROCDLLowerExecutableTargetPass)
+        .addPass(createVerifyWorkgroupDistributionPass);
   }
   variantPassManager.addPass(createReconcileTranslationInfoPass());
   variantPassManager.addPass(IREE::Util::createDropCompilerHintsPass());

compiler/src/iree/compiler/Codegen/SPIRV/Passes.cpp

@@ -631,7 +631,8 @@ void buildSPIRVCodegenPassPipeline(OpPassManager &variantPassManager) {
     modulePassManager.addPass(
         createSPIRVLowerExecutableUsingTransformDialectPass());
     FunctionLikeNest(modulePassManager)
-        .addPass(createSPIRVLowerExecutableTargetPass);
+        .addPass(createSPIRVLowerExecutableTargetPass)
+        .addPass(createVerifyWorkgroupDistributionPass);
     addMemRefLoweringPasses(modulePassManager);
   }
   variantPassManager.addPass(createReconcileTranslationInfoPass());