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[FXML-1871] Implement folding for constant TOSA casts #19
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6b9f7c7
Implement folding for constant TOSA casts
TinaAMD 1bcd322
Replace for/if with if(any_of)
TinaAMD 0222e16
Add information on why the conversion from NaN to int does not expect…
TinaAMD 4659d22
Add more bails for unsupported cast folds
TinaAMD c27805a
Cleanup
TinaAMD 77cb133
Remove unused header
TinaAMD 12b5f8d
Add command line flag to disable folding of integer casts
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213 changes: 213 additions & 0 deletions
213
mlir/lib/Dialect/Tosa/Transforms/TosaFoldConstantCast.cpp
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| Original file line number | Diff line number | Diff line change |
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| //===- TosaFoldConstantCast.cpp -------------------------------------------===// | ||
| // | ||
| // 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 | ||
| // | ||
| //===----------------------------------------------------------------------===// | ||
| // | ||
| // Fold TOSA cast operation on constant data | ||
| // | ||
| //===----------------------------------------------------------------------===// | ||
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| #include "mlir/Dialect/Tosa/IR/TosaOps.h" | ||
| #include "mlir/Dialect/Tosa/Transforms/Passes.h" | ||
| #include "mlir/Dialect/Tosa/Transforms/TosaFoldCommon.h" | ||
| #include "mlir/IR/Matchers.h" | ||
| #include "mlir/Pass/Pass.h" | ||
| #include <llvm/ADT/APFloat.h> | ||
| #include <llvm/ADT/APInt.h> | ||
| #include <llvm/ADT/APSInt.h> | ||
| #include <mlir/IR/BuiltinTypes.h> | ||
| #include <mlir/IR/MLIRContext.h> | ||
| #include <mlir/Support/LogicalResult.h> | ||
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| using namespace mlir; | ||
| using namespace mlir::tosa; | ||
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| namespace { | ||
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| struct TosaFoldConstantCast : public OpRewritePattern<CastOp> { | ||
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| using OpRewritePattern::OpRewritePattern; | ||
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| static APFloat convertIntToFloat(const APInt &toConvert, | ||
| FloatType targetType) { | ||
| APFloat res(targetType.getFloatSemantics()); | ||
| res.convertFromAPInt(toConvert, true /* isSigned */, tosaRoundingMode); | ||
| return res; | ||
| } | ||
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| static APFloat convertFloatToFloat(const APFloat &toConvert, | ||
| FloatType targetType) { | ||
| APFloat res(toConvert); | ||
| bool didLosePrecision; | ||
| res.convert(targetType.getFloatSemantics(), tosaRoundingMode, | ||
| &didLosePrecision); | ||
| return res; | ||
| } | ||
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| static APInt convertFloatToInt(const APFloat &toConvert, | ||
| IntegerType targetType) { | ||
| auto targetWidth = targetType.getIntOrFloatBitWidth(); | ||
| // Converting NaN to an integer results in an unpredictable value. Pick 0. | ||
| if (toConvert.isNaN()) { | ||
| return APInt::getZero(targetWidth); | ||
| } | ||
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| // Make sure to properly translate booleans | ||
| if (targetWidth == 1) { | ||
| return toConvert.isZero() ? APInt::getZero(1) : APInt::getAllOnes(1); | ||
| } | ||
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| // Use the built-in functionality of APFloats to convert to integers. | ||
| // The result of this conversion should be an integer which might still be | ||
| // outside of the target integer range. | ||
| auto floatSize = APFloat::getSizeInBits(toConvert.getSemantics()); | ||
| APSInt converted(std::max(floatSize, targetWidth), targetType.isUnsigned()); | ||
| bool ignored = false; | ||
| toConvert.convertToInteger(converted, APFloat::rmNearestTiesToEven, | ||
| &ignored); | ||
| // Clip to allowed range. | ||
| if (targetWidth < floatSize) { | ||
| if (targetType.isUnsigned()) { | ||
| return converted.truncUSat(targetWidth); | ||
| } | ||
| return converted.truncSSat(targetWidth); | ||
| } | ||
| return converted; | ||
| } | ||
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| static APInt convertIntToInt(const APInt &toConvert, IntegerType targetType) { | ||
| // Make sure to properly translate booleans | ||
| if (targetType.getWidth() == 1) { | ||
| return toConvert.isZero() ? APInt::getZero(1) : APInt::getAllOnes(1); | ||
| } | ||
| if (targetType.isUnsigned()) { | ||
| return toConvert.zextOrTrunc(targetType.getIntOrFloatBitWidth()); | ||
| } | ||
| return toConvert.sextOrTrunc(targetType.getIntOrFloatBitWidth()); | ||
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| } | ||
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| static void warnAboutNaNToIntCast(DenseElementsAttr elements, CastOp location, | ||
| PatternRewriter &rewriter) { | ||
| // This is only relevant if the input values are float | ||
| if (!isa<FloatType>(elements.getElementType())) { | ||
| return; | ||
| } | ||
| // Check if it is an float to integer conversion | ||
| auto resultType = location.getOutput().getType(); | ||
| if (!isa<IntegerType>(cast<TensorType>(resultType).getElementType())) { | ||
| return; | ||
| } | ||
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| // Report encountered NaNs | ||
| auto checkNan = [](const APFloat &val) { return val.isNaN(); }; | ||
| if (any_of(elements.getValues<APFloat>(), checkNan)) { | ||
| location->emitWarning( | ||
| "Float tensor is casted to integer and it contains NaN values. The " | ||
| "cast results in an unspecified value."); | ||
| } | ||
| } | ||
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| LogicalResult matchAndRewrite(CastOp tosaCast, | ||
| PatternRewriter &rewriter) const override { | ||
| auto inputTensor = tosaCast.getInput(); | ||
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| // If the input tensor is not constant, we cannot fold it. | ||
| if (failed(notifyIfNoTosaDenseConstantTensor(inputTensor, tosaCast, | ||
| rewriter))) { | ||
| return failure(); | ||
| } | ||
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| auto fromType = inputTensor.getType().getElementType(); | ||
| auto toType = tosaCast.getOutput().getType().getElementType(); | ||
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| DenseElementsAttr elements; | ||
| matchPattern(inputTensor, m_Constant(&elements)); | ||
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| // Issue a warning if we convert float -> int and NaNs are present; the | ||
| // result value is unspecified in that case | ||
| warnAboutNaNToIntCast(elements, tosaCast, rewriter); | ||
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| // Only fold splat tensors and those used only once to avoid duplicating | ||
| // them. | ||
| if (!inputTensor.hasOneUse() && !isa<SplatElementsAttr>(elements)) { | ||
| return rewriter.notifyMatchFailure(tosaCast, | ||
| "Currently, casts will only be folded " | ||
| "if its input only has a single user"); | ||
| } | ||
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| // Report a match failure for unexpected types | ||
| if (!toType.isIntOrFloat() || !fromType.isIntOrFloat()) { | ||
| return rewriter.notifyMatchFailure( | ||
| tosaCast, "Only casts from/to int/float are supported."); | ||
| } | ||
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| auto isUnsigned = [](Type toCheck) { | ||
| return isa<IntegerType>(toCheck) && | ||
| cast<IntegerType>(toCheck).isUnsigned(); | ||
| }; | ||
| auto typesToCheck = {toType, fromType}; | ||
| if (llvm::any_of(typesToCheck, isUnsigned)) { | ||
| // TOSA casts currently don't support unsigned integers. | ||
| // To support them by here, one could use APSInt instead of APInts, | ||
| // however, this causes trouble with `getValues` which does not support | ||
| // APSInts currently. | ||
| return rewriter.notifyMatchFailure( | ||
| tosaCast, "Cast folding from/to unsigned integers is not supported."); | ||
| } | ||
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| DenseElementsAttr res; | ||
| if (auto intOutTy = dyn_cast<IntegerType>(toType)) { | ||
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| if (isa<FloatType>(fromType)) { | ||
| res = applyElementWise<APFloat, APInt, IntegerType>( | ||
| elements, &convertFloatToInt, intOutTy); | ||
| } else { | ||
| assert(isa<IntegerType>(fromType)); | ||
| res = applyElementWise<APInt, APInt, IntegerType>( | ||
| elements, &convertIntToInt, intOutTy); | ||
| } | ||
| } else { | ||
| assert(isa<FloatType>(toType)); | ||
| auto floatOutTy = cast<FloatType>(toType); | ||
| if (isa<FloatType>(fromType)) { | ||
| res = applyElementWise<APFloat, APFloat, FloatType>( | ||
| elements, &convertFloatToFloat, floatOutTy); | ||
| } else { | ||
| assert(isa<IntegerType>(fromType)); | ||
| res = applyElementWise<APInt, APFloat, FloatType>( | ||
| elements, &convertIntToFloat, floatOutTy); | ||
| } | ||
| } | ||
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| rewriter.replaceOpWithNewOp<ConstOp>(tosaCast, res.getType(), res); | ||
| return success(); | ||
| } | ||
| }; | ||
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| struct TosaFoldConstantFloatCasts : TosaFoldConstantCast { | ||
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| TosaFoldConstantFloatCasts(MLIRContext *ctx) : TosaFoldConstantCast(ctx) {} | ||
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| LogicalResult matchAndRewrite(CastOp tosaCast, | ||
| PatternRewriter &rewriter) const override { | ||
| if (isa<IntegerType>(tosaCast.getInput().getType().getElementType())) { | ||
| return rewriter.notifyMatchFailure( | ||
| tosaCast, "Folding casts from int is currently disabled."); | ||
| } | ||
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| return TosaFoldConstantCast::matchAndRewrite(tosaCast, rewriter); | ||
| } | ||
| }; | ||
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| } // namespace | ||
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| void mlir::tosa::populateTosaFoldConstantCastPatterns( | ||
| MLIRContext *ctx, RewritePatternSet &patterns, bool enableIntCastFolding) { | ||
| if (enableIntCastFolding) { | ||
| patterns.add<TosaFoldConstantCast>(ctx); | ||
| } else { | ||
| patterns.add<TosaFoldConstantFloatCasts>(ctx); | ||
| } | ||
| } | ||
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