[Beignet] [PATCH] Add the PCH support when building the source.

[Zhigang Gong]

This patch really accelerate the compiling speed dramaticlly. Thanks.

One comment as below:

On Mon, Jul 15, 2013 at 06:22:37PM +0800, junyan.he at inbox.com wrote:
> From: Junyan He <junyan.he at linux.intel.com>
> 
> Because the utest grows bigger, the runtime compiling time
> seems a big problem to cause the utest_run very slow.
> Most of the time wastes on re-parsing the big header file
> such as ocl_stdlib.h.
> Using the PCH feature of Clang can shorten the compiling time
> a lot.
> One shortcut: the PCH file in the /tmp/ will not be updated
> automaticly when you modify the ocl_stdlib.h. You should remove
> the pch file manually.
I think this is not convenient for developers and may bring some
confusing. I have two ideas to mitigate or solve this problem:

1. precompile the header file at the gbe's build time. Then we will get an up-to-date
pch file embedded in the gbe library.

2. compute a hash value of the ocl_header.h at gbe's build time, and store this hash
value into the pch file (not very sure whether pch file format can contain any comments
like data, but at least we still can save this hash value to ocl_header.h.hash file at
the same location of the ocl_header.h.pch). At the gbe runtime, we just need to compare
current hash value with the one in the pch file to determine whether we need to update
a new pch file.

The first solution is the ideal solution. And the second is also not too bad, as
we only compute the hash value at gbe's build time and it doesn't bring any overhead
to the application for the hash value computing.

Any thoughts?

> 
> Signed-off-by: Junyan He <junyan.he at linux.intel.com>
> ---
>  backend/src/backend/program.cpp |   54 +++++++++++++++++++++++++++++++++++----
>  1 file changed, 49 insertions(+), 5 deletions(-)
> 
> diff --git a/backend/src/backend/program.cpp b/backend/src/backend/program.cpp
> index 2a4feb9..8f1cf61 100644
> --- a/backend/src/backend/program.cpp
> +++ b/backend/src/backend/program.cpp
> @@ -229,18 +229,62 @@ namespace gbe {
>                                            size_t *errSize)
>    {
>      char clStr[L_tmpnam+1], llStr[L_tmpnam+1];
> +    std::string clOpt;
> +    const std::string header = "/tmp/ocl_header.h";
> +    const std::string header_pch = "/tmp/ocl_header.h.pch";
>      const std::string clName = std::string(tmpnam_r(clStr)) + ".cl"; /* unsafe! */
>      const std::string llName = std::string(tmpnam_r(llStr)) + ".ll"; /* unsafe! */
> -
> -    // Write the source to the cl file
> +    FILE *clHeader = NULL;
>      FILE *clFile = fopen(clName.c_str(), "w");
>      FATAL_IF(clFile == NULL, "Failed to open temporary file");
> -    fwrite(ocl_common_defines_str.c_str(), strlen(ocl_common_defines_str.c_str()), 1, clFile);
> -    fwrite(ocl_stdlib_str.c_str(), strlen(ocl_stdlib_str.c_str()), 1, clFile);
> +
> +    /* Use the header_pch to save the tokenized file. */
> +    if (::access(header_pch.c_str(), R_OK)) {
> +      std::string cmd;
> +      clHeader = fopen(header.c_str(), "w");
> +      FATAL_IF(clHeader == NULL, "Failed to open header file");
> +
> +      fwrite(ocl_common_defines_str.c_str(), strlen(ocl_common_defines_str.c_str()), 1, clHeader);
> +      fwrite(ocl_stdlib_str.c_str(), strlen(ocl_stdlib_str.c_str()), 1, clHeader);
> +      fclose(clHeader);
> +
> +      cmd += "clang -cc1 ";
> +      cmd += "-emit-pch ";
> +      cmd += header;
> +      cmd += " ";
> +      cmd += "-x ";
> +      cmd +=" cl ";
> +
> +#if LLVM_VERSION_MINOR <= 2
> +      cmd +="-triple ";
> +      cmd +="nvptx ";
> +#else
> +      cmd +="-triple ";
> +      cmd +="spir ";
> +#endif /* LLVM_VERSION_MINOR <= 2 */
> +
> +#if LLVM_VERSION_MINOR <= 1
> +      cmd +="-triple ";
> +      cmd +="ptx32 ";
> +#else
> +      cmd += "-ffp-contract=off ";
> +#endif /* LLVM_VERSION_MINOR <= 1 */
> +      cmd += "-o ";
> +      cmd += header_pch;
> +      ::system(cmd.c_str());
> +    }
> +
> +    // Write the source to the cl file
>      fwrite(source, strlen(source), 1, clFile);
>      fclose(clFile);
>  
> -    buildModuleFromSource(clName.c_str(), llName.c_str(), options ? options : "");
> +    clOpt += "-include-pch";
> +    clOpt += " ";
> +    clOpt += header_pch;
> +    clOpt += " ";
> +    if(options)
> +      clOpt += options;
> +    buildModuleFromSource(clName.c_str(), llName.c_str(), clOpt.c_str());
>      remove(clName.c_str());
>  
>      // Now build the program from llvm
> -- 
> 1.7.9.5
> 
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