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//===- BufferUtils.cpp - buffer transformation utilities ------------------===//
//
// Part of the LLVM Project, 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
//
//===----------------------------------------------------------------------===//
//
// This file implements utilities for buffer optimization passes.
//
//===----------------------------------------------------------------------===//
#include "mlir/Transforms/BufferUtils.h"
#include "PassDetail.h"
#include "mlir/Dialect/MemRef/Utils/MemRefUtils.h"
#include "mlir/Dialect/StandardOps/IR/Ops.h"
#include "mlir/IR/Operation.h"
#include "mlir/Interfaces/ControlFlowInterfaces.h"
#include "mlir/Interfaces/LoopLikeInterface.h"
#include "mlir/Pass/Pass.h"
#include "mlir/Transforms/Passes.h"
#include "llvm/ADT/SetOperations.h"
using namespace mlir;
//===----------------------------------------------------------------------===//
// BufferPlacementAllocs
//===----------------------------------------------------------------------===//
/// Get the start operation to place the given alloc value withing the
// specified placement block.
Operation *BufferPlacementAllocs::getStartOperation(Value allocValue,
Block *placementBlock,
const Liveness &liveness) {
// We have to ensure that we place the alloc before its first use in this
// block.
const LivenessBlockInfo &livenessInfo = *liveness.getLiveness(placementBlock);
Operation *startOperation = livenessInfo.getStartOperation(allocValue);
// Check whether the start operation lies in the desired placement block.
// If not, we will use the terminator as this is the last operation in
// this block.
if (startOperation->getBlock() != placementBlock) {
Operation *opInPlacementBlock =
placementBlock->findAncestorOpInBlock(*startOperation);
startOperation = opInPlacementBlock ? opInPlacementBlock
: placementBlock->getTerminator();
}
return startOperation;
}
/// Initializes the internal list by discovering all supported allocation
/// nodes.
BufferPlacementAllocs::BufferPlacementAllocs(Operation *op) { build(op); }
/// Searches for and registers all supported allocation entries.
void BufferPlacementAllocs::build(Operation *op) {
op->walk([&](MemoryEffectOpInterface opInterface) {
// Try to find a single allocation result.
SmallVector<MemoryEffects::EffectInstance, 2> effects;
opInterface.getEffects(effects);
SmallVector<MemoryEffects::EffectInstance, 2> allocateResultEffects;
llvm::copy_if(
effects, std::back_inserter(allocateResultEffects),
[=](MemoryEffects::EffectInstance &it) {
Value value = it.getValue();
return isa<MemoryEffects::Allocate>(it.getEffect()) && value &&
value.isa<OpResult>() &&
it.getResource() !=
SideEffects::AutomaticAllocationScopeResource::get();
});
// If there is one result only, we will be able to move the allocation and
// (possibly existing) deallocation ops.
if (allocateResultEffects.size() != 1)
return;
// Get allocation result.
Value allocValue = allocateResultEffects[0].getValue();
// Find the associated dealloc value and register the allocation entry.
llvm::Optional<Operation *> dealloc = findDealloc(allocValue);
// If the allocation has > 1 dealloc associated with it, skip handling it.
if (!dealloc.hasValue())
return;
allocs.push_back(std::make_tuple(allocValue, *dealloc));
});
}
//===----------------------------------------------------------------------===//
// BufferPlacementTransformationBase
//===----------------------------------------------------------------------===//
/// Constructs a new transformation base using the given root operation.
BufferPlacementTransformationBase::BufferPlacementTransformationBase(
Operation *op)
: aliases(op), allocs(op), liveness(op) {}
/// Returns true if the given operation represents a loop by testing whether it
/// implements the `LoopLikeOpInterface` or the `RegionBranchOpInterface`. In
/// the case of a `RegionBranchOpInterface`, it checks all region-based control-
/// flow edges for cycles.
bool BufferPlacementTransformationBase::isLoop(Operation *op) {
// If the operation implements the `LoopLikeOpInterface` it can be considered
// a loop.
if (isa<LoopLikeOpInterface>(op))
return true;
// If the operation does not implement the `RegionBranchOpInterface`, it is
// (currently) not possible to detect a loop.
RegionBranchOpInterface regionInterface;
if (!(regionInterface = dyn_cast<RegionBranchOpInterface>(op)))
return false;
// Recurses into a region using the current region interface to find potential
// cycles.
SmallPtrSet<Region *, 4> visitedRegions;
std::function<bool(Region *)> recurse = [&](Region *current) {
if (!current)
return false;
// If we have found a back edge, the parent operation induces a loop.
if (!visitedRegions.insert(current).second)
return true;
// Recurses into all region successors.
SmallVector<RegionSuccessor, 2> successors;
regionInterface.getSuccessorRegions(current->getRegionNumber(), successors);
for (RegionSuccessor ®ionEntry : successors)
if (recurse(regionEntry.getSuccessor()))
return true;
return false;
};
// Start with all entry regions and test whether they induce a loop.
SmallVector<RegionSuccessor, 2> successorRegions;
regionInterface.getSuccessorRegions(/*index=*/llvm::None, successorRegions);
for (RegionSuccessor ®ionEntry : successorRegions) {
if (recurse(regionEntry.getSuccessor()))
return true;
visitedRegions.clear();
}
return false;
}
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