README.md - third_party/glslang - Git at Google

 Also see the Khronos landing page for glslang as a reference front end:

 https://www.khronos.org/opengles/sdk/tools/Reference-Compiler/

 The above page includes where to get binaries, and is kept up to date
 regarding the feature level of glslang.

 glslang
 =======

 [![Build Status](https://travis-ci.org/KhronosGroup/glslang.svg?branch=master)](https://travis-ci.org/KhronosGroup/glslang)
 [![Build status](https://ci.appveyor.com/api/projects/status/q6fi9cb0qnhkla68/branch/master?svg=true)](https://ci.appveyor.com/project/Khronoswebmaster/glslang/branch/master)

 An OpenGL and OpenGL ES shader front end and validator.

 There are several components:

 1. A GLSL/ESSL front-end for reference validation and translation of GLSL/ESSL into an AST.

 2. An HLSL front-end for translation of a broad generic HLL into the AST. See [issue 362](https://github.com/KhronosGroup/glslang/issues/362) and [issue 701](https://github.com/KhronosGroup/glslang/issues/701) for current status.

 3. A SPIR-V back end for translating the AST to SPIR-V.

 4. A standalone wrapper, `glslangValidator`, that can be used as a command-line tool for the above.

 How to add a feature protected by a version/extension/stage/profile:  See the
 comment in `glslang/MachineIndependent/Versions.cpp`.

 Tasks waiting to be done are documented as GitHub issues.

 Execution of Standalone Wrapper
 -------------------------------

 To use the standalone binary form, execute `glslangValidator`, and it will print
 a usage statement.  Basic operation is to give it a file containing a shader,
 and it will print out warnings/errors and optionally an AST.

 The applied stage-specific rules are based on the file extension:
 * `.vert` for a vertex shader
 * `.tesc` for a tessellation control shader
 * `.tese` for a tessellation evaluation shader
 * `.geom` for a geometry shader
 * `.frag` for a fragment shader
 * `.comp` for a compute shader

 There is also a non-shader extension
 * `.conf` for a configuration file of limits, see usage statement for example

 Building
 --------

 Instead of building manually, you can also download the binaries for your
 platform directly from the [master-tot release][master-tot-release] on GitHub.
 Those binaries are automatically uploaded by the buildbots after successful
 testing and they always reflect the current top of the tree of the master
 branch.

 ### Dependencies

 * A C++11 compiler.
   (For MSVS: 2015 is recommended, 2013 is fully supported/tested, and 2010 support is attempted, but not tested.)
 * [CMake][cmake]: for generating compilation targets.
 * make: _Linux_, ninja is an alternative, if configured.
 * [Python 3.x][python]: for executing SPIRV-Tools scripts. (Optional if not using SPIRV-Tools and the 'External' subdirectory does not exist.)
 * [bison][bison]: _optional_, but needed when changing the grammar (glslang.y).
 * [googletest][googletest]: _optional_, but should use if making any changes to glslang.

 ### Build steps

 The following steps assume a Bash shell. On Windows, that could be the Git Bash
 shell or some other shell of your choosing.

 #### 1) Check-Out this project

 ```bash
 cd <parent of where you want glslang to be>
 git clone https://github.com/KhronosGroup/glslang.git
 ```

 #### 2) Check-Out External Projects

 ```bash
 cd <the directory glslang was cloned to, "External" will be a subdirectory>
 git clone https://github.com/google/googletest.git External/googletest
 ```

 If you want to use googletest with Visual Studio 2013, you also need to check out an older version:

 ```bash
 # to use googletest with Visual Studio 2013
 cd External/googletest
 git checkout 440527a61e1c91188195f7de212c63c77e8f0a45
 cd ../..
 ```

 If you wish to assure that SPIR-V generated from HLSL is legal for Vulkan,
 or wish to invoke -Os to reduce SPIR-V size from HLSL or GLSL, install
 spirv-tools with this:

 ```bash
 ./update_glslang_sources.py
 ```

 #### 3) Configure

 Assume the source directory is `$SOURCE_DIR` and the build directory is
 `$BUILD_DIR`. First ensure the build directory exists, then navigate to it:

 ```bash
 mkdir -p $BUILD_DIR
 cd $BUILD_DIR
 ```

 For building on Linux:

 ```bash
 cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX="$(pwd)/install" $SOURCE_DIR
 # "Release" (for CMAKE_BUILD_TYPE) could also be "Debug" or "RelWithDebInfo"
 ```

 For building on Windows:

 ```bash
 cmake $SOURCE_DIR -DCMAKE_INSTALL_PREFIX="$(pwd)/install"
 # The CMAKE_INSTALL_PREFIX part is for testing (explained later).
 ```

 The CMake GUI also works for Windows (version 3.4.1 tested).

 Also, consider using `git config --global core.fileMode false` (or with `--local`) on Windows
 to prevent the addition of execution permission on files.

 #### 4) Build and Install

 ```bash
 # for Linux:
 make -j4 install

 # for Windows:
 cmake --build . --config Release --target install
 # "Release" (for --config) could also be "Debug", "MinSizeRel", or "RelWithDebInfo"
 ```

 If using MSVC, after running CMake to configure, use the
 Configuration Manager to check the `INSTALL` project.

 ### If you need to change the GLSL grammar

 The grammar in `glslang/MachineIndependent/glslang.y` has to be recompiled with
 bison if it changes, the output files are committed to the repo to avoid every
 developer needing to have bison configured to compile the project when grammar
 changes are quite infrequent. For windows you can get binaries from
 [GnuWin32][bison-gnu-win32].

 The command to rebuild is:

 ```bash
 m4 -P MachineIndependent/glslang.m4 > MachineIndependent/glslang.y
 bison --defines=MachineIndependent/glslang_tab.cpp.h
       -t MachineIndependent/glslang.y
       -o MachineIndependent/glslang_tab.cpp
 ```

 The above commands are also available in the bash script in `updateGrammar`,
 when executed from the glslang subdirectory of the glslang repository.
 With no arguments it builds the full grammar, and with a "web" argument,
 the web grammar subset (see more about the web subset in the next section).

 ### Building to WASM for the Web and Node

 Use the steps in [Build Steps](#build-steps), with the following notes/exceptions:
 * For building the web subset of core glslang:
   + execute `updateGrammar web` from the glslang subdirectory
     (or if using your own scripts, `m4` needs a `-DGLSLANG_WEB` argument)
   + set `-DENABLE_HLSL=OFF -DBUILD_TESTING=OFF -DENABLE_OPT=OFF -DINSTALL_GTEST=OFF`
   + turn on `-DENABLE_GLSLANG_WEB=ON`
   + optionally, for GLSL compilation error messages, turn on `-DENABLE_GLSLANG_WEB_DEVEL=ON`
 * `emsdk` needs to be present in your executable search path, *PATH* for
   Bash-like enivironments
   + [Instructions located
     here](https://emscripten.org/docs/getting_started/downloads.html#sdk-download-and-install)
 * Wrap cmake call: `emcmake cmake`
 * To get a fully minimized build, make sure to use `brotli` to compress the .js
   and .wasm files

 Example:

 ```sh
 emcmake cmake -DCMAKE_BUILD_TYPE=Release -DENABLE_GLSLANG_WEB=ON \
     -DENABLE_HLSL=OFF -DBUILD_TESTING=OFF -DENABLE_OPT=OFF -DINSTALL_GTEST=OFF ..
 ```

 Testing
 -------

 Right now, there are two test harnesses existing in glslang: one is [Google
 Test](gtests/), one is the [`runtests` script](Test/runtests). The former
 runs unit tests and single-shader single-threaded integration tests, while
 the latter runs multiple-shader linking tests and multi-threaded tests.

 ### Running tests

 The [`runtests` script](Test/runtests) requires compiled binaries to be
 installed into `$BUILD_DIR/install`. Please make sure you have supplied the
 correct configuration to CMake (using `-DCMAKE_INSTALL_PREFIX`) when building;
 otherwise, you may want to modify the path in the `runtests` script.

 Running Google Test-backed tests:

 ```bash
 cd $BUILD_DIR

 # for Linux:
 ctest

 # for Windows:
 ctest -C {Debug|Release|RelWithDebInfo|MinSizeRel}

 # or, run the test binary directly
 # (which gives more fine-grained control like filtering):
 <dir-to-glslangtests-in-build-dir>/glslangtests
 ```

 Running `runtests` script-backed tests:

 ```bash
 cd $SOURCE_DIR/Test && ./runtests
 ```

 ### Contributing tests

 Test results should always be included with a pull request that modifies
 functionality.

 If you are writing unit tests, please use the Google Test framework and
 place the tests under the `gtests/` directory.

 Integration tests are placed in the `Test/` directory. It contains test input
 and a subdirectory `baseResults/` that contains the expected results of the
 tests.  Both the tests and `baseResults/` are under source-code control.

 Google Test runs those integration tests by reading the test input, compiling
 them, and then compare against the expected results in `baseResults/`. The
 integration tests to run via Google Test is registered in various
 `gtests/*.FromFile.cpp` source files. `glslangtests` provides a command-line
 option `--update-mode`, which, if supplied, will overwrite the golden files
 under the `baseResults/` directory with real output from that invocation.
 For more information, please check `gtests/` directory's
 [README](gtests/README.md).

 For the `runtests` script, it will generate current results in the
 `localResults/` directory and `diff` them against the `baseResults/`.
 When you want to update the tracked test results, they need to be
 copied from `localResults/` to `baseResults/`.  This can be done by
 the `bump` shell script.

 You can add your own private list of tests, not tracked publicly, by using
 `localtestlist` to list non-tracked tests.  This is automatically read
 by `runtests` and included in the `diff` and `bump` process.

 Programmatic Interfaces
 -----------------------

 Another piece of software can programmatically translate shaders to an AST
 using one of two different interfaces:
 * A new C++ class-oriented interface, or
 * The original C functional interface

 The `main()` in `StandAlone/StandAlone.cpp` shows examples using both styles.

 ### C++ Class Interface (new, preferred)

 This interface is in roughly the last 1/3 of `ShaderLang.h`.  It is in the
 glslang namespace and contains the following, here with suggested calls
 for generating SPIR-V:

 ```cxx
 const char* GetEsslVersionString();
 const char* GetGlslVersionString();
 bool InitializeProcess();
 void FinalizeProcess();

 class TShader
     setStrings(...);
     setEnvInput(EShSourceHlsl or EShSourceGlsl, stage,  EShClientVulkan or EShClientOpenGL, 100);
     setEnvClient(EShClientVulkan or EShClientOpenGL, EShTargetVulkan_1_0 or EShTargetVulkan_1_1 or EShTargetOpenGL_450);
     setEnvTarget(EShTargetSpv, EShTargetSpv_1_0 or EShTargetSpv_1_3);
     bool parse(...);
     const char* getInfoLog();

 class TProgram
     void addShader(...);
     bool link(...);
     const char* getInfoLog();
     Reflection queries
 ```

 For just validating (not generating code), subsitute these calls:

 ```cxx
     setEnvInput(EShSourceHlsl or EShSourceGlsl, stage,  EShClientNone, 0);
     setEnvClient(EShClientNone, 0);
     setEnvTarget(EShTargetNone, 0);
 ```

 See `ShaderLang.h` and the usage of it in `StandAlone/StandAlone.cpp` for more
 details. There is a block comment giving more detail above the calls for
 `setEnvInput, setEnvClient, and setEnvTarget`.

 ### C Functional Interface (orignal)

 This interface is in roughly the first 2/3 of `ShaderLang.h`, and referred to
 as the `Sh*()` interface, as all the entry points start `Sh`.

 The `Sh*()` interface takes a "compiler" call-back object, which it calls after
 building call back that is passed the AST and can then execute a backend on it.

 The following is a simplified resulting run-time call stack:

 ```c
 ShCompile(shader, compiler) -> compiler(AST) -> <back end>
 ```

 In practice, `ShCompile()` takes shader strings, default version, and
 warning/error and other options for controlling compilation.

 Basic Internal Operation
 ------------------------

 * Initial lexical analysis is done by the preprocessor in
   `MachineIndependent/Preprocessor`, and then refined by a GLSL scanner
   in `MachineIndependent/Scan.cpp`.  There is currently no use of flex.

 * Code is parsed using bison on `MachineIndependent/glslang.y` with the
   aid of a symbol table and an AST.  The symbol table is not passed on to
   the back-end; the intermediate representation stands on its own.
   The tree is built by the grammar productions, many of which are
   offloaded into `ParseHelper.cpp`, and by `Intermediate.cpp`.

 * The intermediate representation is very high-level, and represented
   as an in-memory tree.   This serves to lose no information from the
   original program, and to have efficient transfer of the result from
   parsing to the back-end.  In the AST, constants are propogated and
   folded, and a very small amount of dead code is eliminated.

   To aid linking and reflection, the last top-level branch in the AST
   lists all global symbols.

 * The primary algorithm of the back-end compiler is to traverse the
   tree (high-level intermediate representation), and create an internal
   object code representation.  There is an example of how to do this
   in `MachineIndependent/intermOut.cpp`.

 * Reduction of the tree to a linear byte-code style low-level intermediate
   representation is likely a good way to generate fully optimized code.

 * There is currently some dead old-style linker-type code still lying around.

 * Memory pool: parsing uses types derived from C++ `std` types, using a
   custom allocator that puts them in a memory pool.  This makes allocation
   of individual container/contents just few cycles and deallocation free.
   This pool is popped after the AST is made and processed.

   The use is simple: if you are going to call `new`, there are three cases:

   - the object comes from the pool (its base class has the macro
     `POOL_ALLOCATOR_NEW_DELETE` in it) and you do not have to call `delete`

   - it is a `TString`, in which case call `NewPoolTString()`, which gets
     it from the pool, and there is no corresponding `delete`

   - the object does not come from the pool, and you have to do normal
     C++ memory management of what you `new`


 [cmake]: https://cmake.org/
 [python]: https://www.python.org/
 [bison]: https://www.gnu.org/software/bison/
 [googletest]: https://github.com/google/googletest
 [bison-gnu-win32]: http://gnuwin32.sourceforge.net/packages/bison.htm
 [master-tot-release]: https://github.com/KhronosGroup/glslang/releases/tag/master-tot
	Also see the Khronos landing page for glslang as a reference front end:

	https://www.khronos.org/opengles/sdk/tools/Reference-Compiler/

	The above page includes where to get binaries, and is kept up to date
	regarding the feature level of glslang.

	glslang
	=======

	[![Build Status](https://travis-ci.org/KhronosGroup/glslang.svg?branch=master)](https://travis-ci.org/KhronosGroup/glslang)
	[![Build status](https://ci.appveyor.com/api/projects/status/q6fi9cb0qnhkla68/branch/master?svg=true)](https://ci.appveyor.com/project/Khronoswebmaster/glslang/branch/master)

	An OpenGL and OpenGL ES shader front end and validator.

	There are several components:

	1. A GLSL/ESSL front-end for reference validation and translation of GLSL/ESSL into an AST.

	2. An HLSL front-end for translation of a broad generic HLL into the AST. See [issue 362](https://github.com/KhronosGroup/glslang/issues/362) and [issue 701](https://github.com/KhronosGroup/glslang/issues/701) for current status.

	3. A SPIR-V back end for translating the AST to SPIR-V.

	4. A standalone wrapper, `glslangValidator`, that can be used as a command-line tool for the above.

	How to add a feature protected by a version/extension/stage/profile: See the
	comment in `glslang/MachineIndependent/Versions.cpp`.

	Tasks waiting to be done are documented as GitHub issues.

	Execution of Standalone Wrapper
	-------------------------------

	To use the standalone binary form, execute `glslangValidator`, and it will print
	a usage statement. Basic operation is to give it a file containing a shader,
	and it will print out warnings/errors and optionally an AST.

	The applied stage-specific rules are based on the file extension:
	* `.vert` for a vertex shader
	* `.tesc` for a tessellation control shader
	* `.tese` for a tessellation evaluation shader
	* `.geom` for a geometry shader
	* `.frag` for a fragment shader
	* `.comp` for a compute shader

	There is also a non-shader extension
	* `.conf` for a configuration file of limits, see usage statement for example

	Building
	--------

	Instead of building manually, you can also download the binaries for your
	platform directly from the [master-tot release][master-tot-release] on GitHub.
	Those binaries are automatically uploaded by the buildbots after successful
	testing and they always reflect the current top of the tree of the master
	branch.

	### Dependencies

	* A C++11 compiler.
	(For MSVS: 2015 is recommended, 2013 is fully supported/tested, and 2010 support is attempted, but not tested.)
	* [CMake][cmake]: for generating compilation targets.
	* make: _Linux_, ninja is an alternative, if configured.
	* [Python 3.x][python]: for executing SPIRV-Tools scripts. (Optional if not using SPIRV-Tools and the 'External' subdirectory does not exist.)
	* [bison][bison]: _optional_, but needed when changing the grammar (glslang.y).
	* [googletest][googletest]: _optional_, but should use if making any changes to glslang.

	### Build steps

	The following steps assume a Bash shell. On Windows, that could be the Git Bash
	shell or some other shell of your choosing.

	#### 1) Check-Out this project

	```bash
	cd <parent of where you want glslang to be>
	git clone https://github.com/KhronosGroup/glslang.git
	```

	#### 2) Check-Out External Projects

	```bash
	cd <the directory glslang was cloned to, "External" will be a subdirectory>
	git clone https://github.com/google/googletest.git External/googletest
	```

	If you want to use googletest with Visual Studio 2013, you also need to check out an older version:

	```bash
	# to use googletest with Visual Studio 2013
	cd External/googletest
	git checkout 440527a61e1c91188195f7de212c63c77e8f0a45
	cd ../..
	```

	If you wish to assure that SPIR-V generated from HLSL is legal for Vulkan,
	or wish to invoke -Os to reduce SPIR-V size from HLSL or GLSL, install
	spirv-tools with this:

	```bash
	./update_glslang_sources.py
	```

	#### 3) Configure

	Assume the source directory is `$SOURCE_DIR` and the build directory is
	`$BUILD_DIR`. First ensure the build directory exists, then navigate to it:

	```bash
	mkdir -p $BUILD_DIR
	cd $BUILD_DIR
	```

	For building on Linux:

	```bash
	cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX="$(pwd)/install" $SOURCE_DIR
	# "Release" (for CMAKE_BUILD_TYPE) could also be "Debug" or "RelWithDebInfo"
	```

	For building on Windows:

	```bash
	cmake $SOURCE_DIR -DCMAKE_INSTALL_PREFIX="$(pwd)/install"
	# The CMAKE_INSTALL_PREFIX part is for testing (explained later).
	```

	The CMake GUI also works for Windows (version 3.4.1 tested).

	Also, consider using `git config --global core.fileMode false` (or with `--local`) on Windows
	to prevent the addition of execution permission on files.

	#### 4) Build and Install

	```bash
	# for Linux:
	make -j4 install

	# for Windows:
	cmake --build . --config Release --target install
	# "Release" (for --config) could also be "Debug", "MinSizeRel", or "RelWithDebInfo"
	```

	If using MSVC, after running CMake to configure, use the
	Configuration Manager to check the `INSTALL` project.

	### If you need to change the GLSL grammar

	The grammar in `glslang/MachineIndependent/glslang.y` has to be recompiled with
	bison if it changes, the output files are committed to the repo to avoid every
	developer needing to have bison configured to compile the project when grammar
	changes are quite infrequent. For windows you can get binaries from
	[GnuWin32][bison-gnu-win32].

	The command to rebuild is:

	```bash
	m4 -P MachineIndependent/glslang.m4 > MachineIndependent/glslang.y
	bison --defines=MachineIndependent/glslang_tab.cpp.h
	-t MachineIndependent/glslang.y
	-o MachineIndependent/glslang_tab.cpp
	```

	The above commands are also available in the bash script in `updateGrammar`,
	when executed from the glslang subdirectory of the glslang repository.
	With no arguments it builds the full grammar, and with a "web" argument,
	the web grammar subset (see more about the web subset in the next section).

	### Building to WASM for the Web and Node

	Use the steps in [Build Steps](#build-steps), with the following notes/exceptions:
	* For building the web subset of core glslang:
	+ execute `updateGrammar web` from the glslang subdirectory
	(or if using your own scripts, `m4` needs a `-DGLSLANG_WEB` argument)
	+ set `-DENABLE_HLSL=OFF -DBUILD_TESTING=OFF -DENABLE_OPT=OFF -DINSTALL_GTEST=OFF`
	+ turn on `-DENABLE_GLSLANG_WEB=ON`
	+ optionally, for GLSL compilation error messages, turn on `-DENABLE_GLSLANG_WEB_DEVEL=ON`
	* `emsdk` needs to be present in your executable search path, PATH for
	Bash-like enivironments
	+ [Instructions located
	here](https://emscripten.org/docs/getting_started/downloads.html#sdk-download-and-install)
	* Wrap cmake call: `emcmake cmake`
	* To get a fully minimized build, make sure to use `brotli` to compress the .js
	and .wasm files

	Example:

	```sh
	emcmake cmake -DCMAKE_BUILD_TYPE=Release -DENABLE_GLSLANG_WEB=ON \
	-DENABLE_HLSL=OFF -DBUILD_TESTING=OFF -DENABLE_OPT=OFF -DINSTALL_GTEST=OFF ..
	```

	Testing
	-------

	Right now, there are two test harnesses existing in glslang: one is [Google
	Test](gtests/), one is the [`runtests` script](Test/runtests). The former
	runs unit tests and single-shader single-threaded integration tests, while
	the latter runs multiple-shader linking tests and multi-threaded tests.

	### Running tests

	The [`runtests` script](Test/runtests) requires compiled binaries to be
	installed into `$BUILD_DIR/install`. Please make sure you have supplied the
	correct configuration to CMake (using `-DCMAKE_INSTALL_PREFIX`) when building;
	otherwise, you may want to modify the path in the `runtests` script.

	Running Google Test-backed tests:

	```bash
	cd $BUILD_DIR

	# for Linux:
	ctest

	# for Windows:
	ctest -C {Debug\|Release\|RelWithDebInfo\|MinSizeRel}

	# or, run the test binary directly
	# (which gives more fine-grained control like filtering):
	<dir-to-glslangtests-in-build-dir>/glslangtests
	```

	Running `runtests` script-backed tests:

	```bash
	cd $SOURCE_DIR/Test && ./runtests
	```

	### Contributing tests

	Test results should always be included with a pull request that modifies
	functionality.

	If you are writing unit tests, please use the Google Test framework and
	place the tests under the `gtests/` directory.

	Integration tests are placed in the `Test/` directory. It contains test input
	and a subdirectory `baseResults/` that contains the expected results of the
	tests. Both the tests and `baseResults/` are under source-code control.

	Google Test runs those integration tests by reading the test input, compiling
	them, and then compare against the expected results in `baseResults/`. The
	integration tests to run via Google Test is registered in various
	`gtests/*.FromFile.cpp` source files. `glslangtests` provides a command-line
	option `--update-mode`, which, if supplied, will overwrite the golden files
	under the `baseResults/` directory with real output from that invocation.
	For more information, please check `gtests/` directory's
	[README](gtests/README.md).

	For the `runtests` script, it will generate current results in the
	`localResults/` directory and `diff` them against the `baseResults/`.
	When you want to update the tracked test results, they need to be
	copied from `localResults/` to `baseResults/`. This can be done by
	the `bump` shell script.

	You can add your own private list of tests, not tracked publicly, by using
	`localtestlist` to list non-tracked tests. This is automatically read
	by `runtests` and included in the `diff` and `bump` process.

	Programmatic Interfaces
	-----------------------

	Another piece of software can programmatically translate shaders to an AST
	using one of two different interfaces:
	* A new C++ class-oriented interface, or
	* The original C functional interface

	The `main()` in `StandAlone/StandAlone.cpp` shows examples using both styles.

	### C++ Class Interface (new, preferred)

	This interface is in roughly the last 1/3 of `ShaderLang.h`. It is in the
	glslang namespace and contains the following, here with suggested calls
	for generating SPIR-V:

	```cxx
	const char* GetEsslVersionString();
	const char* GetGlslVersionString();
	bool InitializeProcess();
	void FinalizeProcess();

	class TShader
	setStrings(...);
	setEnvInput(EShSourceHlsl or EShSourceGlsl, stage, EShClientVulkan or EShClientOpenGL, 100);
	setEnvClient(EShClientVulkan or EShClientOpenGL, EShTargetVulkan_1_0 or EShTargetVulkan_1_1 or EShTargetOpenGL_450);
	setEnvTarget(EShTargetSpv, EShTargetSpv_1_0 or EShTargetSpv_1_3);
	bool parse(...);
	const char* getInfoLog();

	class TProgram
	void addShader(...);
	bool link(...);
	const char* getInfoLog();
	Reflection queries
	```

	For just validating (not generating code), subsitute these calls:

	```cxx
	setEnvInput(EShSourceHlsl or EShSourceGlsl, stage, EShClientNone, 0);
	setEnvClient(EShClientNone, 0);
	setEnvTarget(EShTargetNone, 0);
	```

	See `ShaderLang.h` and the usage of it in `StandAlone/StandAlone.cpp` for more
	details. There is a block comment giving more detail above the calls for
	`setEnvInput, setEnvClient, and setEnvTarget`.

	### C Functional Interface (orignal)

	This interface is in roughly the first 2/3 of `ShaderLang.h`, and referred to
	as the `Sh*()` interface, as all the entry points start `Sh`.

	The `Sh*()` interface takes a "compiler" call-back object, which it calls after
	building call back that is passed the AST and can then execute a backend on it.

	The following is a simplified resulting run-time call stack:

	```c
	ShCompile(shader, compiler) -> compiler(AST) -> <back end>
	```

	In practice, `ShCompile()` takes shader strings, default version, and
	warning/error and other options for controlling compilation.

	Basic Internal Operation
	------------------------

	* Initial lexical analysis is done by the preprocessor in
	`MachineIndependent/Preprocessor`, and then refined by a GLSL scanner
	in `MachineIndependent/Scan.cpp`. There is currently no use of flex.

	* Code is parsed using bison on `MachineIndependent/glslang.y` with the
	aid of a symbol table and an AST. The symbol table is not passed on to
	the back-end; the intermediate representation stands on its own.
	The tree is built by the grammar productions, many of which are
	offloaded into `ParseHelper.cpp`, and by `Intermediate.cpp`.

	* The intermediate representation is very high-level, and represented
	as an in-memory tree. This serves to lose no information from the
	original program, and to have efficient transfer of the result from
	parsing to the back-end. In the AST, constants are propogated and
	folded, and a very small amount of dead code is eliminated.

	To aid linking and reflection, the last top-level branch in the AST
	lists all global symbols.

	* The primary algorithm of the back-end compiler is to traverse the
	tree (high-level intermediate representation), and create an internal
	object code representation. There is an example of how to do this
	in `MachineIndependent/intermOut.cpp`.

	* Reduction of the tree to a linear byte-code style low-level intermediate
	representation is likely a good way to generate fully optimized code.

	* There is currently some dead old-style linker-type code still lying around.

	* Memory pool: parsing uses types derived from C++ `std` types, using a
	custom allocator that puts them in a memory pool. This makes allocation
	of individual container/contents just few cycles and deallocation free.
	This pool is popped after the AST is made and processed.

	The use is simple: if you are going to call `new`, there are three cases:

	- the object comes from the pool (its base class has the macro
	`POOL_ALLOCATOR_NEW_DELETE` in it) and you do not have to call `delete`

	- it is a `TString`, in which case call `NewPoolTString()`, which gets
	it from the pool, and there is no corresponding `delete`

	- the object does not come from the pool, and you have to do normal
	C++ memory management of what you `new`


	[cmake]: https://cmake.org/
	[python]: https://www.python.org/
	[bison]: https://www.gnu.org/software/bison/
	[googletest]: https://github.com/google/googletest
	[bison-gnu-win32]: http://gnuwin32.sourceforge.net/packages/bison.htm
	[master-tot-release]: https://github.com/KhronosGroup/glslang/releases/tag/master-tot