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    306 <body>
    307 <div class="document" id="llvm-rs-cc-compiler-for-renderscript-language">
    308 <h1 class="title">llvm-rs-cc: Compiler for Renderscript language</h1>
    309 
    310 <div class="section" id="introduction">
    311 <h1>Introduction</h1>
    312 <p>llvm-rs-cc compiles a program in the Renderscript language to generate the
    313 following files:</p>
    314 <ul class="simple">
    315 <li>Bitcode file. Note that the bitcode here denotes the LLVM (Low-Level
    316 Virtual Machine) bitcode representation, which will be consumed on
    317 an Android device by libbcc (in
    318 platform/frameworks/compile/libbcc.git) to generate device-specific
    319 executables.</li>
    320 <li>Reflected APIs for Java. As a result, Android's Java developers can
    321 invoke those APIs from their code.</li>
    322 </ul>
    323 <p>Note that although Renderscript is C99-like, we enhance it with several
    324 distinct, effective features for Android programming. We will use
    325 some examples to illustrate these features.</p>
    326 <p>llvm-rs-cc is run on the host and performs many aggressive optimizations.
    327 As a result, libbcc on the device can be lightweight and focus on
    328 machine-dependent code generation for some input bitcode.</p>
    329 <p>llvm-rs-cc is a driver on top of libslang. The architecture of
    330 libslang and libbcc is depicted in the following figure:</p>
    331 <pre class="literal-block">
    332 libslang   libbcc
    333     |   \   |
    334     |    \  |
    335  clang     llvm
    336 </pre>
    337 </div>
    338 <div class="section" id="usage">
    339 <h1>Usage</h1>
    340 <ul>
    341 <li><p class="first"><em>-o $(PRIVATE_RS_OUTPUT_DIR)/res/raw</em></p>
    342 <p>This option specifies the directory for outputting a .bc file.</p>
    343 </li>
    344 <li><p class="first"><em>-p $(PRIVATE_RS_OUTPUT_DIR)/src</em></p>
    345 <p>The option <em>-p</em> denotes the directory for outputting the reflected Java files.</p>
    346 </li>
    347 <li><p class="first"><em>-d $(PRIVATE_RS_OUTPUT_DIR)</em></p>
    348 <p>This option <em>-d</em> sets the directory for writing dependence information.</p>
    349 </li>
    350 <li><p class="first"><em>-MD</em></p>
    351 <p>Note that <em>-MD</em> will tell llvm-rs-cc to output dependence information.</p>
    352 </li>
    353 <li><p class="first"><em>-a $(EXTRA_TARGETS)</em></p>
    354 <p>Specifies additional target dependencies.</p>
    355 </li>
    356 </ul>
    357 </div>
    358 <div class="section" id="example-command">
    359 <h1>Example Command</h1>
    360 <p>First:</p>
    361 <pre class="literal-block">
    362 $ cd &lt;Android_Root_Directory&gt;
    363 </pre>
    364 <p>Using frameworks/base/tests/RenderScriptTests/Fountain as a simple app in both
    365 Java and Renderscript, we can find the following command line in the build
    366 log:</p>
    367 <pre class="literal-block">
    368 $ out/host/linux-x86/bin/llvm-rs-cc \
    369   -o out/target/common/obj/APPS/Fountain_intermediates/src/renderscript/res/raw \
    370   -p out/target/common/obj/APPS/Fountain_intermediates/src/renderscript/src \
    371   -d out/target/common/obj/APPS/Fountain_intermediates/src/renderscript \
    372   -a out/target/common/obj/APPS/Fountain_intermediates/src/RenderScript.stamp \
    373   -MD \
    374   -I frameworks/base/libs/rs/scriptc \
    375   -I external/clang/lib/Headers \
    376   frameworks/base/libs/rs/java/Fountain/src/com/android/fountain/fountain.rs
    377 </pre>
    378 <p>This command will generate:</p>
    379 <ul class="simple">
    380 <li><strong>fountain.bc</strong></li>
    381 <li><strong>ScriptC_fountain.java</strong></li>
    382 <li><strong>ScriptField_Point.java</strong></li>
    383 </ul>
    384 <p>The <strong>Script*.java</strong> files above will be documented below.</p>
    385 </div>
    386 <div class="section" id="example-program-fountain-rs">
    387 <h1>Example Program: fountain.rs</h1>
    388 <p>fountain.rs is in the Renderscript language, which is based on the standard
    389 C99. However, llvm-rs-cc goes beyond &quot;clang -std=c99&quot; and provides the
    390 following important features:</p>
    391 </div>
    392 <div class="section" id="pragma">
    393 <h1>1. Pragma</h1>
    394 <ul>
    395 <li><p class="first"><em>#pragma rs java_package_name([PACKAGE_NAME])</em></p>
    396 <p>The ScriptC_[SCRIPT_NAME].java has to be packaged so that Java
    397 developers can invoke those APIs.</p>
    398 <p>To do that, a Renderscript programmer should specify the package name, so
    399 that llvm-rs-cc knows the package expression and hence the directory
    400 for outputting ScriptC_[SCRIPT_NAME].java.</p>
    401 <p>In fountain.rs, we have:</p>
    402 <pre class="literal-block">
    403 #pragma rs java_package_name(com.android.fountain)
    404 </pre>
    405 <p>In ScriptC_fountain.java, we have:</p>
    406 <pre class="literal-block">
    407 package com.android.fountain
    408 </pre>
    409 <p>Note that the ScriptC_fountain.java will be generated inside
    410 ./com/android/fountain/.</p>
    411 </li>
    412 <li><p class="first">#pragma version(1)</p>
    413 <p>This pragma is for evolving the language. Currently we are at
    414 version 1 of the language.</p>
    415 </li>
    416 </ul>
    417 </div>
    418 <div class="section" id="basic-reflection-export-variables-and-functions">
    419 <h1>2. Basic Reflection: Export Variables and Functions</h1>
    420 <p>llvm-rs-cc automatically exports the &quot;externalizable and defined&quot; functions and
    421 variables to Android's Java side. That is, scripts are accessible from
    422 Java.</p>
    423 <p>For instance, for:</p>
    424 <pre class="literal-block">
    425 int foo = 0;
    426 </pre>
    427 <p>In ScriptC_fountain.java, llvm-rs-cc will reflect the following methods:</p>
    428 <pre class="literal-block">
    429 void set_foo(int v)...
    430 
    431 int get_foo()...
    432 </pre>
    433 <p>This access takes the form of generated classes which provide access
    434 to the functions and global variables within a script. In summary,
    435 global variables and functions within a script that are not declared
    436 static will generate get, set, or invoke methods.  This provides a way
    437 to set the data within a script and call its functions.</p>
    438 <p>Take the addParticles function in fountain.rs as an example:</p>
    439 <pre class="literal-block">
    440 void addParticles(int rate, float x, float y, int index, bool newColor) {
    441   ...
    442 }
    443 </pre>
    444 <p>llvm-rs-cc will genearte ScriptC_fountain.java as follows:</p>
    445 <pre class="literal-block">
    446 void invoke_addParticles(int rate, float x, float y,
    447                          int index, bool newColor) {
    448   ...
    449 }
    450 </pre>
    451 </div>
    452 <div class="section" id="export-user-defined-structs">
    453 <h1>3. Export User-Defined Structs</h1>
    454 <p>In fountain.rs, we have:</p>
    455 <pre class="literal-block">
    456 typedef struct __attribute__((packed, aligned(4))) Point {
    457   float2 delta;
    458   float2 position;
    459   uchar4 color;
    460 } Point_t;
    461 
    462 Point_t *point;
    463 </pre>
    464 <p>llvm-rs-cc generates one ScriptField*.java file for each user-defined
    465 struct. In this case, llvm-rs-cc will reflect two files,
    466 ScriptC_fountain.java and ScriptField_Point.java.</p>
    467 <p>Note that when the type of an exportable variable is a structure, Renderscript
    468 developers should avoid using anonymous structs. This is because llvm-rs-cc
    469 uses the struct name to identify the file, instead of the typedef name.</p>
    470 <p>For the generated Java files, using ScriptC_fountain.java as an
    471 example we also have:</p>
    472 <pre class="literal-block">
    473 void bind_point(ScriptField_Point v)
    474 </pre>
    475 <p>This binds your object with the allocated memory.</p>
    476 <p>You can bind the struct(e.g., Point), using the setter and getter
    477 methods in ScriptField_Point.java.</p>
    478 <p>After binding, you can access the object with this method:</p>
    479 <pre class="literal-block">
    480 ScriptField_Point get_point()
    481 </pre>
    482 <p>In ScriptField_Point_s.java:</p>
    483 <pre class="literal-block">
    484 ...
    485 // Copying the Item, which is the object that stores every
    486 // fields of struct, to the *index*\-th entry of byte array.
    487 //
    488 // In general, this method would not be invoked directly
    489 // but is used to implement the setter.
    490 void copyToArray(Item i, int index)
    491 
    492 // The setter of Item array,
    493 // index: the index of the Item array
    494 // copyNow: If true, it will be copied to the *index*\-th entry
    495 // of byte array.
    496 void set(Item i, int index, boolean copyNow)
    497 
    498 // The getter of Item array, which gets the *index*-th element
    499 // of byte array.
    500 Item get(int index)
    501 
    502 set_delta(int index, Float2 v, boolean copyNow)
    503 
    504 // The following is the individual setters and getters of
    505 // each field of a struct.
    506 public void set_delta(int index, Float2 v, boolean copyNow)
    507 public void set_position(int index, Float2 v, boolean copyNow)
    508 public void set_color(int index, Short4 v, boolean copyNow)
    509 public Float2 get_delta(int index)
    510 public Float2 get_position(int index)
    511 public Short4 get_color(int index)
    512 
    513 // Copying all Item array to byte array (i.e., memory allocation).
    514 void copyAll()
    515 ...
    516 </pre>
    517 </div>
    518 <div class="section" id="summary-of-the-java-reflection-above">
    519 <h1>4. Summary of the Java Reflection above</h1>
    520 <p>This section summarizes the high-level design of Renderscript's reflection.</p>
    521 <ul>
    522 <li><p class="first">In terms of a script's global functions, they can be called from Java.
    523 These calls operate asynchronously and no assumptions should be made
    524 on whether a function called will have actually completed operation.  If it
    525 is necessary to wait for a function to complete, the Java application
    526 may call the runtime finish() method, which will wait for all the script
    527 threads to complete pending operations.  A few special functions can also
    528 exist:</p>
    529 <ul>
    530 <li><p class="first">The function <strong>init</strong> (if present) will be called once after the script
    531 is loaded.  This is useful to initialize data or anything else the
    532 script may need before it can be used.  The init function may not depend
    533 on globals initialized from Java as it will be called before these
    534 can be initialized. The function signature for init must be:</p>
    535 <pre class="literal-block">
    536 void init(void);
    537 </pre>
    538 </li>
    539 <li><p class="first">The function <strong>root</strong> is a special function for graphics.  This function
    540 will be called when a script must redraw its contents.  No
    541 assumptions should be made as to when this function will be
    542 called.  It will only be called if the script is bound as a graphics root.
    543 Calls to this function will be synchronized with data updates and
    544 other invocations from Java.  Thus the script will not change due
    545 to external influence in the middle of running <strong>root</strong>.  The return value
    546 indicates to the runtime when the function should be called again to
    547 redraw in the future.  A return value of 0 indicates that no
    548 redraw is necessary until something changes on the Java side.  Any
    549 positive integer indicates a time in milliseconds that the runtime should
    550 wait before calling root again to render another frame.  The function
    551 signature for a graphics root functions is as follows:</p>
    552 <pre class="literal-block">
    553 int root(void);
    554 </pre>
    555 </li>
    556 <li><p class="first">It is also possible to create a purely compute-based <strong>root</strong> function.
    557 Such a function has the following signature:</p>
    558 <pre class="literal-block">
    559 void root(const T1 *in, T2 *out, const T3 *usrData, uint32_t x, uint32_t y);
    560 </pre>
    561 <p>T1, T2, and T3 represent any supported Renderscript type.  Any parameters
    562 above can be omitted, although at least one of in/out must be present.
    563 If both in and out are present, root must only be invoked with types of
    564 the same exact dimensionality (i.e. matching X and Y values for dimension).
    565 This root function is accessible through the Renderscript language
    566 construct <strong>forEach</strong>.  We also reflect a Java version to access this
    567 function as <strong>forEach_root</strong> (for API levels of 14+).  An example of this
    568 can be seen in the Android SDK sample for HelloCompute.</p>
    569 </li>
    570 <li><p class="first">The function <strong>.rs.dtor</strong> is a function that is sometimes generated by
    571 llvm-rs-cc.  This function cleans up any global variable that contains
    572 (or is) a reference counted Renderscript object type (such as an
    573 rs_allocation, rs_font, or rs_script).  This function will be invoked
    574 implicitly by the Renderscript runtime during script teardown.</p>
    575 </li>
    576 </ul>
    577 </li>
    578 <li><p class="first">In terms of a script's global data, global variables can be written
    579 from Java.  The Java instance will cache the value or object set and
    580 provide return methods to retrieve this value.  If a script updates
    581 the value, this update will not propagate back to the Java class.
    582 Initializers, if present, will also initialize the cached Java value.
    583 This provides a convenient way to declare constants within a script and
    584 make them accessible to the Java runtime.  If the script declares a
    585 variable const, only the get methods will be generated.</p>
    586 <p>Globals within a script are considered local to the script.  They
    587 cannot be accessed by other scripts and are in effect always 'static'
    588 in the traditional C sense.  Static here is used to control if
    589 accessors are generated.  Static continues to mean <em>not
    590 externally visible</em> and thus prevents the generation of
    591 accessors.  Globals are persistent across invocations of a script and
    592 thus may be used to hold data from run to run.</p>
    593 <p>Globals of two types may be reflected into the Java class.  The first
    594 type is basic non-pointer types.  Types defined in rs_types.rsh may also be
    595 used.  For the non-pointer class, get and set methods are generated for
    596 Java.  Globals of single pointer types behave differently.  These may
    597 use more complex types.  Simple structures composed of the types in
    598 rs_types.rsh may also be used.  These globals generate bind points in
    599 Java.  If the type is a structure they also generate an appropriate
    600 <strong>Field</strong> class that is used to pack and unpack the contents of the
    601 structure.  Binding an allocation in Java effectively sets the
    602 pointer in the script.  Bind points marked const indicate to the
    603 runtime that the script will not modify the contents of an allocation.
    604 This may allow the runtime to make more effective use of threads.</p>
    605 </li>
    606 </ul>
    607 </div>
    608 <div class="section" id="vector-types">
    609 <h1>5. Vector Types</h1>
    610 <p>Vector types such as float2, float4, and uint4 are included to support
    611 vector processing in environments where the processors provide vector
    612 instructions.</p>
    613 <p>On non-vector systems the same code will continue to run but without
    614 the performance advantage.  Function overloading is also supported.
    615 This allows the runtime to support vector version of the basic math
    616 routines without the need for special naming.  For instance,</p>
    617 <ul class="simple">
    618 <li><em>float sin(float);</em></li>
    619 <li><em>float2 sin(float2);</em></li>
    620 <li><em>float3 sin(float3);</em></li>
    621 <li><em>float4 sin(float4);</em></li>
    622 </ul>
    623 </div>
    624 </div>
    625 </body>
    626 </html>
    627