E6033

Error · Topology/Hardware

E6033 — An index into a tensor in a scope: thread space that is not known when compiling. Such a tensor stays in registers, and a register has no address. So each index must be a constant, or made of constants and the variables of for loops with constant bounds, at most 1024 passes each. The code generator unrolls those loops.

What the compiler reports

Error[E6033] at 22:6: the register tensor 'acc' needs an index that is known when compiling: 'n' is not a constant or the variable of a `for` loop. A tensor in a `scope: thread` space stays in registers, which have no address
Error[E6033] at 28:8: the register tensor 'acc' needs an index that is known when compiling: the bounds of the loop of 'i' are not constants, so the compiler cannot unroll it
Error[E6033] at 35:8: the register tensor 'acc' needs an index that is known when compiling: the loop of 'i' has 2000 passes, and the compiler unrolls at most 1024
Error[E6033] at 41:6: the register tensor 'acc' needs an index that is known when compiling: the index uses a value that is not a constant or a loop variable

The fragments the test suite holds the compiler to. An ellipsis marks text the test does not constrain; the emitted message also carries a source location.

A program that triggers it

//
// Part of the Vx Project, under the Apache License v2.0 with LLVM Exceptions.
// See LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
// A tensor in `Memory::REG` (`scope: thread`) stays in registers, so each index must be known
// when compiling. Each function below indexes one with something else.
//

fn three() on Topology::Device -> i32 {
  return 3;
}

fn with_a_parameter(acc : &mut Tensor<f32, [32], Memory::REG>, n : i32) on Topology::Device -> void {
  acc[n] = 1.0;
  return;
}

fn with_loop_bounds_not_known(acc : &mut Tensor<f32, [32], Memory::REG>, n : i32) on Topology::Device -> void {
  for i in 0..n {
    acc[i] = 1.0;
  }
  return;
}

fn with_a_long_loop(acc : &mut Tensor<f32, [32], Memory::REG>) on Topology::Device -> void {
  for i in 0..2000 {
    acc[i % 32] = 1.0;
  }
  return;
}

fn with_a_call(acc : &mut Tensor<f32, [32], Memory::REG>) on Topology::Device -> void {
  acc[three()] = 1.0;
  return;
}

fn main() -> i32 {
  return 0;
}

From tests/frontend/fail/register_tensor_indexes_not_known_when_compiling.vx, which asserts this diagnostic on every commit.

Related