Vitis HLS LLVM examples

Examples of how to use Vitis HLS with a local LLVM build and/or custom LLVM opt passes.

Example	Description
override_llvm_flow_demo	How to use local LLVM build within Vitis HLS. Local LLVM will be used for both clang and opt phases.
override_opt_flow_demo	How to use local LLVM opt binary within Vitis HLS.
plugin_analyze_rename_flow_demo	How to call a custom LLVM opt pass within Vitis HLS. Requires plugins/example_analyze_rename to be built. Does not require a local LLVM build.
plugin_auto_array_partition_flow_demo	How to use the auto_array_partition plugin within Vitis HLS. Requires plugins/auto_array_partition plugin to be built. Does not require a local LLVM build.

Note that the override* examples assume that the local LLVM binaries have some customized behavior/passes which will be called implicitly or explicitly in the run_hls.tcl.

How to run Vitis HLS project examples

1. Build local LLVM and/or custom passes.
2. Install Xilinx Vitis HLS
3. Source Xilinx Vitis_HLS settings64.sh/csh.
4. Run the following from within the example's directory:

vitis_hls run_hls.tcl

High level flow

Using LLVM in Vitis HLS

In order to use a local LLVM build or a custom LLVM pass in Vitis HLS you must set one of the following variables:

Variable Name	Variable Type	Description
XILINX_OPEN_SOURCE_LLVM_BUILD_PATH	Environment	Path to local LLVM build. Use clang/clang-tools-extra/opt binaries from this location.
::LLVM_CUSTOM_CMD	TCL global	Specify additional clang/opt command(s) to be run during csynth_design.

LLVM_CUSTOM_CMD related variables

When setting the ::LLVM_CUSTOM_CMD TCL variable you may also set the following optional TCL variables.

Variable Name	Description
::LLVM_CUSTOM_OUTPUT	File path of output bc file.
::LLVM_CUSTOM_INPUT	File path of input bc file.
::LLVM_CUSTOM_OPT	File path of opt binary. When XILINX_OPEN_SOURCE_LLVM_BUILD_PATH is not set this is used to override only opt and not other llvm/clang binaries.

Within the ::LLVM_CUSTOM_CMD variable value you may reference the following TCL variables. Note: do not use the global namespace (::) when referencing these variables.

Variable Use	Description
$LLVM_CUSTOM_OUTPUT	File path of output bc file.
$LLVM_CUSTOM_INPUT	File path of input bc file.
$LLVM_CUSTOM_OPT	File path of opt binary.

Within the ::LLVM_CUSTOM_CMD variable value you may reference any environment variables using standard $::env(name) TCL syntax (i.e. $::env(XILINX_OPEN_SOURCE_LLVM_BUILD_PATH)).

Copyright 2016-2022 Xilinx, Inc. Copyright (C) 2023, Advanced Micro Devices, Inc. SPDX-License-Identifier: Apache-2.0