Update INSTALL.md

INSTALL.md

@@ -5,6 +5,7 @@
 - [Installing pre-built packages](#installing-pre-built-packages)
   * [Prerequisites](#prerequisites)
   * [AMD-hcc](#amd-hcc)
+  * [AMD-clang](#amd-clang)
   * [NVIDIA-nvcc](#nvidia-nvcc)
   * [Verify your installation](#verify-your-installation)
 - [Building HIP from source](#building-hip-from-source)
@@ -18,7 +19,7 @@
 HIP can be easily installed using pre-built binary packages using the package manager for your platform.
 
 ## Prerequisites
-HIP code can be developed either on AMD ROCm platform using hcc compiler, or a CUDA platform with nvcc installed:
+HIP code can be developed either on AMD ROCm platform using hcc or clang compiler, or a CUDA platform with nvcc installed:
 
 ## AMD-hcc
 
@@ -31,6 +32,38 @@ HIP code can be developed either on AMD ROCm platform using hcc compiler, or a C
    * By default HIP is installed into /opt/rocm/hip (can be overridden by setting HIP_PATH environment variable).
    * Optionally, consider adding /opt/rocm/bin to your PATH to make it easier to use the tools.
 
+## AMD-clang
+
+* Using clang to compile HIP program for AMD GPU is under development. Users need to build LLVM, clang, lld, ROCm device library, and HIP from source.
+
+* Install the [rocm](http://gpuopen.com/getting-started-with-boltzmann-components-platforms-installation/) packages.  ROCm will install some of the necessary components, including the kernel driver, HSA runtime, etc.
+
+* Build LLVM/clang/lld by using the following repository and branch and following the general LLVM/clang build procedure:
+
+   * LLVM: https://github.com/RadeonOpenCompute/llvm.git amd-common branch
+   * clang: https://github.com/RadeonOpenCompute/clang checkout amd-hip-upstream branch, then merge with amd-common branch to match LLVM/lld
+   * lld: https://github.com/RadeonOpenCompute/lld amd-common branch
+   
+* Build Rocm device library
+
+   * Checkout https://github.com/RadeonOpenCompute/ROCm-Device-Libs.git amd-hip branch and build it with clang built from the last step.
+   
+* Build HIP
+
+   * Checkout https://github.com/ROCm-Developer-Tools/HIP.git hip-clang branch and build it with HCC installed with ROCm packages.
+   
+* Environment variables to let hipcc to use clang to compile HIP program
+
+   By default hipcc uses hcc to compile HIP program for AMD GPU. To let hipcc to use clang to compile HIP program, the following environment variables must be set:
+
+   * HIP_CLANG_PATH - Path to clang   
+   * DEVICE_LIB_PATH - Path to the device library
+   
+* Default paths and environment variables:
+
+   * By default HIP looks for HSA in /opt/rocm/hsa (can be overridden by setting HSA_PATH environment variable) 
+   * By default HIP is installed into /opt/rocm/hip (can be overridden by setting HIP_PATH environment variable).
+   * Optionally, consider adding /opt/rocm/bin to your PATH to make it easier to use the tools.
 
 ## NVIDIA-nvcc
 * Configure the additional package server as described [here](http://gpuopen.com/getting-started-with-boltzmann-components-platforms-installation/).