[mlir][math] Expand powfI operation for constant power operand. #87081
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,12 +1,12 @@ | ||
| //===- ExpandPatterns.cpp - Code to expand various math operations. -------===// | ||
| // | ||
| // 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 expansion of various math operations. | ||
| // | ||
| //===----------------------------------------------------------------------===// | ||
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@@ -23,9 +23,14 @@ | |
| using namespace mlir; | ||
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| /// Create a float constant. | ||
| static Value createFloatConst(Location loc, Type type, APFloat value, | ||
| OpBuilder &b) { | ||
| bool losesInfo = false; | ||
| auto eltType = getElementTypeOrSelf(type); | ||
| // Convert double to the given `FloatType` with round-to-nearest-ties-to-even. | ||
| value.convert(cast<FloatType>(eltType).getFloatSemantics(), | ||
| APFloat::rmNearestTiesToEven, &losesInfo); | ||
| auto attr = b.getFloatAttr(eltType, value); | ||
| if (auto shapedTy = dyn_cast<ShapedType>(type)) { | ||
| return b.create<arith::ConstantOp>(loc, | ||
| DenseElementsAttr::get(shapedTy, attr)); | ||
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@@ -34,7 +39,12 @@ static Value createFloatConst(Location loc, Type type, double value, | |
| return b.create<arith::ConstantOp>(loc, attr); | ||
| } | ||
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| static Value createFloatConst(Location loc, Type type, double value, | ||
| OpBuilder &b) { | ||
| return createFloatConst(loc, type, APFloat(value), b); | ||
| } | ||
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| /// Create an integer constant. | ||
| static Value createIntConst(Location loc, Type type, int64_t value, | ||
| OpBuilder &b) { | ||
| auto attr = b.getIntegerAttr(getElementTypeOrSelf(type), value); | ||
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@@ -202,6 +212,69 @@ static LogicalResult convertCeilOp(math::CeilOp op, PatternRewriter &rewriter) { | |
| rewriter.replaceOp(op, ret); | ||
| return success(); | ||
| } | ||
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| // Convert `math.fpowi` to a series of `arith.mulf` operations. | ||
| // If the power is negative, we divide one by the result. | ||
| // If both the base and power are zero, the result is 1. | ||
| static LogicalResult convertFPowICstOp(math::FPowIOp op, | ||
| PatternRewriter &rewriter) { | ||
| ImplicitLocOpBuilder b(op->getLoc(), rewriter); | ||
| Value base = op.getOperand(0); | ||
| Value power = op.getOperand(1); | ||
| Type baseType = base.getType(); | ||
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| Attribute cstAttr; | ||
| if (!matchPattern(power, m_Constant(&cstAttr))) | ||
| return failure(); | ||
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| APInt value; | ||
| if (!matchPattern(cstAttr, m_ConstantInt(&value))) | ||
| return failure(); | ||
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| int64_t powerInt = value.getSExtValue(); | ||
| bool isNegative = powerInt < 0; | ||
| int64_t absPower = std::abs(powerInt); | ||
| Value one = createFloatConst(op->getLoc(), baseType, 1.00, rewriter); | ||
| Value res = createFloatConst(op->getLoc(), baseType, 1.00, rewriter); | ||
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| while (absPower > 0) { | ||
| if (absPower & 1) | ||
| res = b.create<arith::MulFOp>(baseType, base, res); | ||
| absPower >>= 1; | ||
| base = b.create<arith::MulFOp>(baseType, base, base); | ||
| } | ||
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| // Make sure not to introduce UB in case of negative power. | ||
| if (isNegative) { | ||
| auto &sem = dyn_cast<mlir::FloatType>(getElementTypeOrSelf(baseType)) | ||
| .getFloatSemantics(); | ||
| Value zero = | ||
| createFloatConst(op->getLoc(), baseType, | ||
| APFloat::getZero(sem, /*Negative=*/false), rewriter); | ||
| Value negZero = | ||
| createFloatConst(op->getLoc(), baseType, | ||
| APFloat::getZero(sem, /*Negative=*/true), rewriter); | ||
| Value posInfinity = | ||
| createFloatConst(op->getLoc(), baseType, | ||
| APFloat::getInf(sem, /*Negative=*/false), rewriter); | ||
| Value negInfinity = | ||
| createFloatConst(op->getLoc(), baseType, | ||
| APFloat::getInf(sem, /*Negative=*/true), rewriter); | ||
| Value zeroEqCheck = | ||
| b.create<arith::CmpFOp>(arith::CmpFPredicate::OEQ, res, zero); | ||
| Value negZeroEqCheck = | ||
| b.create<arith::CmpFOp>(arith::CmpFPredicate::OEQ, res, negZero); | ||
| res = b.create<arith::DivFOp>(baseType, one, res); | ||
| res = | ||
| b.create<arith::SelectOp>(op->getLoc(), zeroEqCheck, posInfinity, res); | ||
| res = b.create<arith::SelectOp>(op->getLoc(), negZeroEqCheck, negInfinity, | ||
| res); | ||
| } | ||
|
There was a problem hiding this comment. What happens when both the base and the power are zero? I checked the llvm langref and it doesn't mention this case: https://llvm.org/docs/LangRef.html#llvm-powi-intrinsic . The c standard library is more informative here: https://en.cppreference.com/w/cpp/numeric/math/pow#:~:text=in%20math_errhandling.-,If,is%20negative%2C%20a%20domain%20error%20or%20a%20pole%20error%20may%20occur.,-If%20the%20implementation . Because neither There was a problem hiding this comment. I have added this information in the doc comments. I also experimented with PyTorch and Python. They both give 1 as an output. So we're good to go. go. |
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| rewriter.replaceOp(op, res); | ||
| return success(); | ||
| } | ||
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| // Converts Powf(float a, float b) (meaning a^b) to exp^(b * ln(a)) | ||
| static LogicalResult convertPowfOp(math::PowFOp op, PatternRewriter &rewriter) { | ||
| ImplicitLocOpBuilder b(op->getLoc(), rewriter); | ||
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@@ -517,6 +590,10 @@ void mlir::populateExpandPowFPattern(RewritePatternSet &patterns) { | |
| patterns.add(convertPowfOp); | ||
| } | ||
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| void mlir::populateExpandFPowIPattern(RewritePatternSet &patterns) { | ||
| patterns.add(convertFPowICstOp); | ||
| } | ||
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| void mlir::populateExpandRoundFPattern(RewritePatternSet &patterns) { | ||
| patterns.add(convertRoundOp); | ||
| } | ||
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