[GitHub] [tvm] ibsidorenko commented on a diff in pull request #12659: [Hexagon] Implement fixed_point_multiply op through intrinsics.

[GitBox <gi...@apache.org>]

ibsidorenko commented on code in PR #12659:
URL: https://github.com/apache/tvm/pull/12659#discussion_r960256617


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python/tvm/topi/hexagon/tensor_intrin.py:
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@@ -0,0 +1,71 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+"""Optimized implementation of q_multiply_shift based on LLVM intrinsics"""
+
+import tvm
+from tvm.ir import register_intrin_lowering
+
+
+def _q_multiply_shift_hexagon(op):
+    """
+    Implementation of q_multiply_shift through hexagon intrinsics vmpyewuh and vmpyowh when q == 31.
+
+    Please note that this is introducing a small round-up error for some corner cases with negative
+    shift argument. This is because we are rounding twice instead than only once. I.e.:
+
+        * original q_multiply_shift: round(x*y*2^-s)
+        * hexagon q_multiply_shift: round(round(x*y)*2^-s)
+    """
+    x = op.args[0]
+    y = op.args[1]
+    fractional_bits = op.args[2]
+    shift = op.args[3]
+
+    # Don't use this intrinsic if we don't have a int32x32 vector
+    # or if we are not multiplying q31 numbers
+    if x.dtype != "int32x32" or fractional_bits.value != 31:
+        return op
+
+    # Case 1, shift is negative
+    mul_e_1 = tvm.tir.call_llvm_intrin(
+        op.dtype, "llvm.hexagon.V6.vmpyewuh.128B", tvm.tir.const(2, "uint32"), x, y
+    )
+    mul_o_1 = tvm.tir.call_llvm_intrin(
+        op.dtype, "llvm.hexagon.V6.vmpyowh.rnd.sacc.128B", tvm.tir.const(3, "uint32"), mul_e_1, x, y
+    )
+    fixup = mul_o_1 & (-shift)
+    round_mul = mul_o_1 + fixup
+    out_negative_shift = tvm.tir.call_llvm_intrin(
+        op.dtype, "llvm.hexagon.V6.vaslwv.128B", tvm.tir.const(2, "uint32"), round_mul, shift
+    )
+
+    # Case 2, shift is positive
+    x = x * (1 << (shift))
+    mul_e_2 = tvm.tir.call_llvm_intrin(
+        op.dtype, "llvm.hexagon.V6.vmpyewuh.128B", tvm.tir.const(2, "uint32"), x, y
+    )
+    mul_o_2 = tvm.tir.call_llvm_intrin(
+        op.dtype, "llvm.hexagon.V6.vmpyowh.rnd.sacc.128B", tvm.tir.const(3, "uint32"), mul_e_2, x, y
+    )
+
+    # Select depending on the shift
+    return tvm.tir.Select(shift < 0, out_negative_shift, mul_o_2)

Review Comment:
   hm... Maybe I misunderstood the question, but I put shift separately before mul_o_2:
   `x = x * (1 << (shift))`



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