1350c9887d
This commit defines a dataflow analysis for integer ranges, which uses a newly-added InferIntRangeInterface to compute the lower and upper bounds on the results of an operation from the bounds on the arguments. The range inference is a flow-insensitive dataflow analysis that can be used to simplify code, such as by statically identifying bounds checks that cannot fail in order to eliminate them. The InferIntRangeInterface has one method, inferResultRanges(), which takes a vector of inferred ranges for each argument to an op implementing the interface and a callback allowing the implementation to define the ranges for each result. These ranges are stored as ConstantIntRanges, which hold the lower and upper bounds for a value. Bounds are tracked separately for the signed and unsigned interpretations of a value, which ensures that the impact of arithmetic overflows is correctly tracked during the analysis. The commit also adds a -test-int-range-inference pass to test the analysis until it is integrated into SCCP or otherwise exposed. Finally, this commit fixes some bugs relating to the handling of region iteration arguments and terminators in the data flow analysis framework. Depends on D124020 Depends on D124021 Reviewed By: rriddle, Mogball Differential Revision: https://reviews.llvm.org/D124023
116 lines
4.0 KiB
C++
116 lines
4.0 KiB
C++
//===- TestIntRangeInference.cpp - Create consts from range inference ---===//
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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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// TODO: This pass is needed to test integer range inference until that
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// functionality has been integrated into SCCP.
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//===----------------------------------------------------------------------===//
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#include "mlir/Analysis/IntRangeAnalysis.h"
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#include "mlir/Interfaces/SideEffectInterfaces.h"
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#include "mlir/Pass/Pass.h"
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#include "mlir/Pass/PassRegistry.h"
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#include "mlir/Support/TypeID.h"
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#include "mlir/Transforms/FoldUtils.h"
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using namespace mlir;
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/// Patterned after SCCP
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static LogicalResult replaceWithConstant(IntRangeAnalysis &analysis,
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OpBuilder &b, OperationFolder &folder,
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Value value) {
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Optional<ConstantIntRanges> maybeInferredRange = analysis.getResult(value);
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if (!maybeInferredRange)
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return failure();
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const ConstantIntRanges &inferredRange = maybeInferredRange.getValue();
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Optional<APInt> maybeConstValue = inferredRange.getConstantValue();
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if (!maybeConstValue.hasValue())
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return failure();
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Operation *maybeDefiningOp = value.getDefiningOp();
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Dialect *valueDialect =
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maybeDefiningOp ? maybeDefiningOp->getDialect()
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: value.getParentRegion()->getParentOp()->getDialect();
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Attribute constAttr = b.getIntegerAttr(value.getType(), *maybeConstValue);
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Value constant = folder.getOrCreateConstant(b, valueDialect, constAttr,
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value.getType(), value.getLoc());
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if (!constant)
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return failure();
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value.replaceAllUsesWith(constant);
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return success();
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}
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static void rewrite(IntRangeAnalysis &analysis, MLIRContext *context,
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MutableArrayRef<Region> initialRegions) {
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SmallVector<Block *> worklist;
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auto addToWorklist = [&](MutableArrayRef<Region> regions) {
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for (Region ®ion : regions)
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for (Block &block : llvm::reverse(region))
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worklist.push_back(&block);
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};
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OpBuilder builder(context);
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OperationFolder folder(context);
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addToWorklist(initialRegions);
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while (!worklist.empty()) {
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Block *block = worklist.pop_back_val();
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for (Operation &op : llvm::make_early_inc_range(*block)) {
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builder.setInsertionPoint(&op);
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// Replace any result with constants.
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bool replacedAll = op.getNumResults() != 0;
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for (Value res : op.getResults())
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replacedAll &=
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succeeded(replaceWithConstant(analysis, builder, folder, res));
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// If all of the results of the operation were replaced, try to erase
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// the operation completely.
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if (replacedAll && wouldOpBeTriviallyDead(&op)) {
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assert(op.use_empty() && "expected all uses to be replaced");
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op.erase();
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continue;
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}
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// Add any the regions of this operation to the worklist.
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addToWorklist(op.getRegions());
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}
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// Replace any block arguments with constants.
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builder.setInsertionPointToStart(block);
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for (BlockArgument arg : block->getArguments())
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(void)replaceWithConstant(analysis, builder, folder, arg);
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}
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}
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namespace {
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struct TestIntRangeInference
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: PassWrapper<TestIntRangeInference, OperationPass<>> {
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MLIR_DEFINE_EXPLICIT_INTERNAL_INLINE_TYPE_ID(TestIntRangeInference)
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StringRef getArgument() const final { return "test-int-range-inference"; }
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StringRef getDescription() const final {
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return "Test integer range inference analysis";
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}
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void runOnOperation() override {
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Operation *op = getOperation();
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IntRangeAnalysis analysis(op);
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rewrite(analysis, op->getContext(), op->getRegions());
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}
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};
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} // end anonymous namespace
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namespace mlir {
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namespace test {
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void registerTestIntRangeInference() {
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PassRegistration<TestIntRangeInference>();
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}
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} // end namespace test
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} // end namespace mlir
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