Update README.md

README.md

@@ -12,19 +12,45 @@ You would need to download and install the following components for using AVX an
 * Intel OpenCL SDK for Linux from [software.intel.com/sdk/opencl](software.intel.com/sdk/opencl). Follow the installation instructions (no special requirements).
 * CUDA
 
-## Build
+## Getting source code and building HPVM
 
-Switch to hpvm-reorg-9
+Checkout HPVM:
 ```shell
-git checkout hpvm-reorg-9
+* git clone https://gitlab.engr.illinois.edu/llvm/hpvm.git
+* git checkout hpvm-reorg-9 (this step may not be needed once code is mirrored on Github)
 ```
 
-Build hpvm
+HPVM installer script can be used to dowwnload, configure and build HPMV along with LLVM and other subprojects including Clang. 
 ```shell
-bash install.sh
+* bash install.sh
 ```
+Specifically, the HPVM installer downloads the LLVM, Clang, compiler-rt, libcxxabi and lld, copies HPVM source into 
+llvm/tools and build the entire tree. LLVM C-Backend is also built as a part of HPVM and is currently used to perform 
+code generation in OpenCL for GPUs. The script provides you with an option to choose number of threads.
 
-Build hpvm runtime 
+Alternatively, CMake can be run manually.
+```shell
+* cd hpvm/build
+* cmake ../llvm [options]
+```
+Some common options that can be used with CMake are:
+```shell
+* -DCMAKE_INSTALL_PREFIX=directory
+```
+--- Specify for directory the full pathname of where you want the HPVM tools and libraries to be installed.
+
+```shell
+-DCMAKE_BUILD_TYPE=type
+```
+--- Valid options for type are Debug, Release, RelWithDebInfo, and MinSizeRel. Default is Debug.
+
+```shell
+-DLLVM_ENABLE_ASSERTIONS=On
+```
+--- Compile with assertion checks enabled (default is Yes for Debug builds, No for all other build types).
+
+#Building hpvm runtime
+HPVM also includes a runtime library which comprises of low-level, target-specific wrappers required by HPVM's code generation.
 ```shell
 cd projects/visc-rt
 make