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[MLIR][Affine] Fix affine data copy generation copy placement for missing memref definition check #130750

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Merged
merged 1 commit into from
Mar 13, 2025
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[MLIR][Affine] Fix affine data copy generation copy placement for missing memref definition check #130750

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34 changes: 24 additions & 10 deletions mlir/lib/Dialect/Affine/Utils/LoopUtils.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1774,23 +1774,37 @@ findHighestBlockForPlacement(const MemRefRegion &region, Block &block,
SmallVector<Value, 4> symbols;
cst->getValues(cst->getNumDimVars(), cst->getNumDimAndSymbolVars(), &symbols);

SmallVector<AffineForOp, 4> enclosingFors;
getAffineForIVs(*block.begin(), &enclosingFors);
SmallVector<Operation *, 4> enclosingAffineOps;
getEnclosingAffineOps(*block.begin(), &enclosingAffineOps);
// Walk up loop parents till we find an IV on which this region is
// symbolic/variant.
auto it = enclosingFors.rbegin();
for (auto e = enclosingFors.rend(); it != e; ++it) {
// symbolic/variant or we hit `hoistGuard`.
auto it = enclosingAffineOps.rbegin();
AffineForOp lastInvariantFor;
for (auto e = enclosingAffineOps.rend(); it != e; ++it) {
Operation *enclosingOp = *it;
// We can't hoist past the definition of the memref being copied.
Value memref = region.memref;
if (!memref.getParentRegion()->isAncestor(enclosingOp->getParentRegion())) {
LLVM_DEBUG(
llvm::dbgs()
<< "memref definition will end up not dominating hoist location\n");
break;
}

auto affineFor = dyn_cast<AffineForOp>(enclosingOp);
if (!affineFor)
break;
// TODO: also need to be checking this for regions symbols that
// aren't loop IVs, whether we are within their resp. defs' dominance scope.
if (llvm::is_contained(symbols, it->getInductionVar()))
if (llvm::is_contained(symbols, affineFor.getInductionVar()))
break;
lastInvariantFor = affineFor;
}

if (it != enclosingFors.rbegin()) {
auto lastInvariantIV = *std::prev(it);
*copyInPlacementStart = Block::iterator(lastInvariantIV.getOperation());
if (it != enclosingAffineOps.rbegin()) {
*copyInPlacementStart = Block::iterator(lastInvariantFor);
*copyOutPlacementStart = std::next(*copyInPlacementStart);
*copyPlacementBlock = lastInvariantIV->getBlock();
*copyPlacementBlock = lastInvariantFor->getBlock();
} else {
*copyInPlacementStart = begin;
*copyOutPlacementStart = end;
Expand Down
16 changes: 16 additions & 0 deletions mlir/test/Dialect/Affine/affine-data-copy.mlir
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Expand Up @@ -8,6 +8,7 @@
// affine.load op in the innermost loop as a filter.
// RUN: mlir-opt %s -split-input-file -test-affine-data-copy='memref-filter' | FileCheck %s --check-prefix=FILTER
// RUN: mlir-opt %s -split-input-file -test-affine-data-copy='for-memref-region' | FileCheck %s --check-prefix=MEMREF_REGION
// RUN: mlir-opt %s -split-input-file -test-affine-data-copy='capacity-kib=32' | FileCheck %s --check-prefix=LIMITED-MEM

// -copy-skip-non-stride-loops forces the copies to be placed right inside the
// tile space loops, avoiding the sensitivity of copy placement depth to memory
Expand All @@ -23,6 +24,7 @@

// CHECK-LABEL: func @matmul
// FILTER-LABEL: func @matmul
// LIMITED-MEM-LABEL: func @matmul
func.func @matmul(%A: memref<4096x4096xf32>, %B: memref<4096x4096xf32>, %C: memref<4096x4096xf32>) -> memref<4096x4096xf32> {
affine.for %i = 0 to 4096 step 128 {
affine.for %j = 0 to 4096 step 128 {
Expand All @@ -43,6 +45,7 @@ func.func @matmul(%A: memref<4096x4096xf32>, %B: memref<4096x4096xf32>, %C: memr
}
}
return %C : memref<4096x4096xf32>
// LIMITED-MEM: return
}

// Buffers of size 128x128 get created here for all three matrices.
Expand Down Expand Up @@ -421,6 +424,7 @@ func.func @scalar_memref_copy_in_loop(%3:memref<480xi1>) {
}

// CHECK-LABEL: func @memref_def_inside
// LIMITED-MEM-LABEL: func @memref_def_inside
func.func @memref_def_inside(%arg0: index) {
%0 = llvm.mlir.constant(1.000000e+00 : f32) : f32
// No copy generation can happen at this depth given the definition inside.
Expand All @@ -429,5 +433,17 @@ func.func @memref_def_inside(%arg0: index) {
// CHECK: affine.store {{.*}} : memref<1xf32>
affine.store %0, %alloc_7[0] : memref<1xf32>
}

// With the limited capacity specified, buffer generation happens at the
// innermost depth. Tests that copy-placement is proper and respects the
// memref definition.

// LIMITED-MEM: affine.for %{{.*}} = 0 to 29
// LIMITED-MEM-NEXT: memref.alloc() : memref<1xf32>
// LIMITED-MEM-NEXT: memref.alloc() : memref<1xf32>
// LIMITED-MEM-NEXT: affine.store %{{.*}}, %{{.*}}[0] : memref<1xf32>
// LIMITED-MEM-NEXT: affine.load %{{.*}}[%c0{{.*}}] : memref<1xf32>
// LIMITED-MEM-NEXT: affine.store %{{.*}}, %{{.*}}[0] : memref<1xf32>
// LIMITED-MEM-NEXT: memref.dealloc %{{.*}} : memref<1xf32>
return
}
19 changes: 14 additions & 5 deletions mlir/test/lib/Dialect/Affine/TestAffineDataCopy.cpp
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Expand Up @@ -53,6 +53,11 @@ struct TestAffineDataCopy
*this, "for-memref-region",
llvm::cl::desc("Test copy generation for a single memref region"),
llvm::cl::init(false)};
Option<uint64_t> clCapacityLimit{
*this, "capacity-kib",
llvm::cl::desc("Test copy generation enforcing a limit of capacity "
"(default: unlimited)"),
llvm::cl::init(UINT64_MAX)};
};

} // namespace
Expand All @@ -73,24 +78,24 @@ void TestAffineDataCopy::runOnOperation() {
auto loopNest = depthToLoops[0][0];
auto innermostLoop = depthToLoops[innermostLoopIdx][0];
AffineLoadOp load;
// For simplicity, these options are tested on the first memref being loaded
// from in the innermost loop.
if (clMemRefFilter || clTestGenerateCopyForMemRegion) {
// Gather MemRef filter. For simplicity, we use the first loaded memref
// found in the innermost loop.
for (auto &op : *innermostLoop.getBody()) {
if (auto ld = dyn_cast<AffineLoadOp>(op)) {
load = ld;
break;
}
}
if (!load)
return;
}
if (!load)
return;

AffineCopyOptions copyOptions = {/*generateDma=*/false,
/*slowMemorySpace=*/0,
/*fastMemorySpace=*/0,
/*tagMemorySpace=*/0,
/*fastMemCapacityBytes=*/32 * 1024 * 1024UL};
/*fastMemCapacityBytes=*/clCapacityLimit};
DenseSet<Operation *> copyNests;
if (clMemRefFilter) {
if (failed(affineDataCopyGenerate(loopNest, copyOptions, load.getMemRef(),
Expand All @@ -103,6 +108,10 @@ void TestAffineDataCopy::runOnOperation() {
return;
if (failed(generateCopyForMemRegion(region, loopNest, copyOptions, result)))
return;
} else if (failed(affineDataCopyGenerate(loopNest, copyOptions,
/*filterMemref=*/std::nullopt,
copyNests))) {
return;
}

// Promote any single iteration loops in the copy nests and simplify
Expand Down