[Mlir-commits] [mlir] Introduce `arith.scaling_extf` and `arith.scaling_truncf` (PR #141965)

[Krzysztof Drewniak]

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@@ -409,6 +421,112 @@ 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);
+    auto inputOperand = op.getIn();
+    auto scaleOperand = op.getScale();
+    if (!llvm::isa<Float8E8M0FNUType>(getElementTypeOrSelf(scaleOperand))) {
+      return rewriter.notifyMatchFailure(
+          op, "scaling extf is not using scale operand of type f8E8M0FNU");
+    }
+    Type resultTy = op.getType();
+    // extf on scale will essentially create f32 number 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);
+    auto inputOperand = op.getIn();
+    auto scaleOperand = op.getScale();
+    if (!llvm::isa<Float8E8M0FNUType>(getElementTypeOrSelf(scaleOperand))) {
+      return rewriter.notifyMatchFailure(
+          op, "scaling truncf is not using scale operand of type f8E8M0FNU");
+    }
+    auto scaleTy = scaleOperand.getType();
+
+    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());
+    Type f8Ty = cloneToShapedType(resultTy, b.getF8E8M0Type());
+
+    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 in result type as per
+    // the OCP MXFP spec
+    // https://github.com/microsoft/microxcaling/blob/7bc41952de394f5cc5e782baf132e7c7542eb4e4/mx/mx_ops.py#L277
+    const llvm::fltSemantics &resultFltSemantics =
+        llvm::cast<FloatType>(resultETy).getFloatSemantics();
+    int maxExponent = APFloat::semanticsMaxExponent(resultFltSemantics);
+    Value cMaxNormalExponent =
----------------
krzysz00 wrote:

Skip all this if we're in f32 or higher?

https://github.com/llvm/llvm-project/pull/141965