308571074c
This is an artifact from merging MLIR into LLVM, the file headers are now aligned with the rest of the project.
97 lines
3.4 KiB
C++
97 lines
3.4 KiB
C++
//===- LoopCoalescing.cpp - Pass transforming loop nests into single loops-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#include "mlir/Dialect/LoopOps/LoopOps.h"
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#include "mlir/Dialect/StandardOps/Ops.h"
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#include "mlir/Pass/Pass.h"
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#include "mlir/Transforms/LoopUtils.h"
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#include "mlir/Transforms/Passes.h"
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#include "mlir/Transforms/RegionUtils.h"
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#include "llvm/Support/Debug.h"
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#define PASS_NAME "loop-coalescing"
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#define DEBUG_TYPE PASS_NAME
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using namespace mlir;
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namespace {
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class LoopCoalescingPass : public FunctionPass<LoopCoalescingPass> {
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public:
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void runOnFunction() override {
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FuncOp func = getFunction();
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func.walk([](loop::ForOp op) {
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// Ignore nested loops.
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if (op.getParentOfType<loop::ForOp>())
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return;
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SmallVector<loop::ForOp, 4> loops;
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getPerfectlyNestedLoops(loops, op);
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LLVM_DEBUG(llvm::dbgs()
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<< "found a perfect nest of depth " << loops.size() << '\n');
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// Look for a band of loops that can be coalesced, i.e. perfectly nested
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// loops with bounds defined above some loop.
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// 1. For each loop, find above which parent loop its operands are
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// defined.
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SmallVector<unsigned, 4> operandsDefinedAbove(loops.size());
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for (unsigned i = 0, e = loops.size(); i < e; ++i) {
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operandsDefinedAbove[i] = i;
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for (unsigned j = 0; j < i; ++j) {
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if (areValuesDefinedAbove(loops[i].getOperands(),
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loops[j].region())) {
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operandsDefinedAbove[i] = j;
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break;
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}
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}
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LLVM_DEBUG(llvm::dbgs()
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<< " bounds of loop " << i << " are known above depth "
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<< operandsDefinedAbove[i] << '\n');
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}
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// 2. Identify bands of loops such that the operands of all of them are
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// defined above the first loop in the band. Traverse the nest bottom-up
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// so that modifications don't invalidate the inner loops.
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for (unsigned end = loops.size(); end > 0; --end) {
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unsigned start = 0;
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for (; start < end - 1; ++start) {
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auto maxPos =
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*std::max_element(std::next(operandsDefinedAbove.begin(), start),
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std::next(operandsDefinedAbove.begin(), end));
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if (maxPos > start)
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continue;
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assert(maxPos == start &&
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"expected loop bounds to be known at the start of the band");
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LLVM_DEBUG(llvm::dbgs() << " found coalesceable band from " << start
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<< " to " << end << '\n');
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auto band =
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llvm::makeMutableArrayRef(loops.data() + start, end - start);
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coalesceLoops(band);
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break;
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}
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// If a band was found and transformed, keep looking at the loops above
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// the outermost transformed loop.
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if (start != end - 1)
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end = start + 1;
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}
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});
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}
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};
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} // namespace
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std::unique_ptr<OpPassBase<FuncOp>> mlir::createLoopCoalescingPass() {
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return std::make_unique<LoopCoalescingPass>();
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}
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static PassRegistration<LoopCoalescingPass>
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reg(PASS_NAME,
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"coalesce nested loops with independent bounds into a single loop");
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