[Mlir-commits] [mlir] Introduce `arith.scaling_extf` and `arith.scaling_truncf` (PR #141965)
Umang Yadav
llvmlistbot at llvm.org
Sat May 31 05:18:56 PDT 2025
================
@@ -409,6 +421,125 @@ struct F8E8M0TruncFOpConverter : public OpRewritePattern<arith::TruncFOp> {
}
};
+struct ScalingExtFOpConverter : public OpRewritePattern<arith::ScalingExtFOp> {
+ using OpRewritePattern::OpRewritePattern;
+ LogicalResult matchAndRewrite(arith::ScalingExtFOp op,
+ PatternRewriter &rewriter) const final {
+ ImplicitLocOpBuilder b(op.getLoc(), rewriter);
+ Value inputOperand = op.getIn();
+ Value scaleOperand = op.getScale();
+ Type scaleETy = getElementTypeOrSelf(scaleOperand);
+ // allow implicit exponent extraction from 16/32 bits floats
+ if (scaleETy.getIntOrFloatBitWidth() >= 16) {
+ scaleETy = b.getF8E8M0Type();
+ scaleOperand = b.create<arith::TruncFOp>(scaleETy, scaleOperand);
+ }
+ if (!llvm::isa<Float8E8M0FNUType>(scaleETy)) {
+ return rewriter.notifyMatchFailure(
+ op, "scaling_extf is using scales of type which can not be converted "
+ "to f8E8M0FNU");
+ }
+ Type resultTy = op.getType();
+ // extf on scale will essentially create floating point number
+ // of type resulTy that is 2^scale and will also propagate NaNs
+ Value scaleExt = b.create<arith::ExtFOp>(resultTy, scaleOperand);
+ Value inputExt = b.create<arith::ExtFOp>(resultTy, inputOperand);
+ Value result = b.create<arith::MulFOp>(inputExt, scaleExt);
+ rewriter.replaceOp(op, result);
+ return success();
+ }
+};
+
+struct ScalingTruncFOpConverter
+ : public OpRewritePattern<arith::ScalingTruncFOp> {
+ using OpRewritePattern::OpRewritePattern;
+ LogicalResult matchAndRewrite(arith::ScalingTruncFOp op,
+ PatternRewriter &rewriter) const final {
+ ImplicitLocOpBuilder b(op.getLoc(), rewriter);
+ Value inputOperand = op.getIn();
+ Value scaleOperand = op.getScale();
+ Type scaleTy = scaleOperand.getType();
+ Type scaleETy = getElementTypeOrSelf(scaleOperand);
+ // allow implicit exponent extraction from 16/32 bits floats
+ if (scaleETy.getIntOrFloatBitWidth() >= 16) {
+ scaleETy = b.getF8E8M0Type();
+ scaleOperand = b.create<arith::TruncFOp>(scaleETy, scaleOperand);
+ scaleTy = scaleOperand.getType();
+ }
+ if (!llvm::isa<Float8E8M0FNUType>(scaleETy)) {
+ return rewriter.notifyMatchFailure(
+ op, "scaling_truncf is using scales type which can not be converted "
+ "to f8E8M0FNU");
+ }
+
+ Type resultTy = op.getType();
+ Type resultETy = getElementTypeOrSelf(op.getOut());
+
+ Type inputTy = inputOperand.getType();
+ Type inputETy = getElementTypeOrSelf(inputOperand);
+
+ Type i8Ty = cloneToShapedType(resultTy, b.getI8Type());
+ Type i32Ty = cloneToShapedType(resultTy, b.getI32Type());
+ Type f32Ty = cloneToShapedType(resultTy, b.getF32Type());
+
+ if (inputETy.getIntOrFloatBitWidth() < 32) {
+ inputOperand = b.create<arith::ExtFOp>(f32Ty, inputOperand);
+ } else if (inputETy.getIntOrFloatBitWidth() > 32) {
+ inputOperand = b.create<arith::TruncFOp>(f32Ty, inputOperand);
+ }
+ inputTy = inputOperand.getType();
+ inputETy = getElementTypeOrSelf(inputOperand);
+
+ // normalize scale by exponent of the max normal value (emax) in result type
+ // as per the OCP MXFP spec
+ // https://github.com/microsoft/microxcaling/blob/7bc41952de394f5cc5e782baf132e7c7542eb4e4/mx/mx_ops.py#L277
+ // here this normalization is carried in f32. Therefore instead of
+ // subtraction it does the DivFOp
+ const llvm::fltSemantics &resultFltSemantics =
+ llvm::cast<FloatType>(resultETy).getFloatSemantics();
+ int maxExponent = APFloat::semanticsMaxExponent(resultFltSemantics);
+ Value cEmax = createConst(op->getLoc(), i32Ty, maxExponent, rewriter);
+ Value c1 = createConst(op->getLoc(), i32Ty, 1, rewriter);
+ Value cPow2 = b.create<arith::ShLIOp>(c1, cEmax);
+ Value cPow2F32 = b.create<arith::SIToFPOp>(f32Ty, cPow2);
+ Value scaleF32 = b.create<arith::ExtFOp>(f32Ty, scaleOperand);
+ // note that spec also does the clamping but it should only be done for
+ // underflows because diving by 2^emax will only make it smaller.
----------------
umangyadav wrote:
```suggestion
// underflows because dividing by 2^emax will only make it smaller.
```
https://github.com/llvm/llvm-project/pull/141965
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