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| <title>LLVM 1.5 Release Notes</title> | |
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| <body> | |
| <div class="doc_title">LLVM 1.5 Release Notes</div> | |
| <ol> | |
| <li><a href="#intro">Introduction</a></li> | |
| <li><a href="#whatsnew">What's New?</a></li> | |
| <li><a href="GettingStarted.html">Installation Instructions</a></li> | |
| <li><a href="#portability">Portability and Supported Platforms</a></li> | |
| <li><a href="#knownproblems">Known Problems</a> | |
| <li><a href="#additionalinfo">Additional Information</a></li> | |
| </ol> | |
| <div class="doc_author"> | |
| <p>Written by the <a href="http://llvm.cs.uiuc.edu">LLVM Team</a><p> | |
| </div> | |
| <!-- *********************************************************************** --> | |
| <div class="doc_section"> | |
| <a name="intro">Introduction</a> | |
| </div> | |
| <!-- *********************************************************************** --> | |
| <div class="doc_text"> | |
| <p>This document contains the release notes for the LLVM compiler | |
| infrastructure, release 1.5. Here we describe the status of LLVM, including any | |
| known problems and major improvements from the previous release. The most | |
| up-to-date version of this document can be found on the <a | |
| href="http://llvm.cs.uiuc.edu/releases/1.5/">LLVM 1.5 web site</a>. If you are | |
| not reading this on the LLVM web pages, you should probably go there because | |
| this document may be updated after the release.</p> | |
| <p>For more information about LLVM, including information about the latest | |
| release, please check out the <a href="http://llvm.cs.uiuc.edu">main LLVM | |
| web site</a>. If you have questions or comments, the <a | |
| href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM developer's mailing | |
| list</a> is a good place to send them.</p> | |
| <p>Note that if you are reading this file from CVS or the main LLVM web page, | |
| this document applies to the <i>next</i> release, not the current one. To see | |
| the release notes for the current or previous releases, see the <a | |
| href="http://llvm.cs.uiuc.edu/releases/">releases page</a>.</p> | |
| </div> | |
| <!-- *********************************************************************** --> | |
| <div class="doc_section"> | |
| <a name="whatsnew">What's New?</a> | |
| </div> | |
| <!-- *********************************************************************** --> | |
| <div class="doc_text"> | |
| <p>This is the sixth public release of the LLVM Compiler Infrastructure.</p> | |
| <p>LLVM 1.5 is known to correctly compile a wide range of C and C++ programs, | |
| includes bug fixes for those problems found since the 1.4 release, and includes | |
| a large number of new features and enhancements, described below.</p> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="newfeatures">New Features in LLVM 1.5</a> | |
| </div> | |
| <!--_________________________________________________________________________--> | |
| <div class="doc_subsubsection"><a name="newcg">New Native Code | |
| Generators</a></div> | |
| <div class="doc_text"> | |
| <p> | |
| This release includes new native code generators for <a | |
| href="#alpha-be">Alpha</a>, <a href="#ia64-be">IA-64</a>, and <a | |
| href="#sparcv8">SPARC-V8</a> (32-bit SPARC). These code generators are still | |
| beta quality, but are progressing rapidly. The Alpha backend is implemented | |
| with an eye towards being compatible with the widely used SimpleScalar | |
| simulator. | |
| </p> | |
| </div> | |
| <!--_________________________________________________________________________--> | |
| <div class="doc_subsubsection"><a name="selectiondag">New Instruction | |
| Selector Framework</a></div> | |
| <div class="doc_text"> | |
| <p>This release includes a <a href="CodeGenerator.html#instselect">new framework | |
| for building instruction selectors</a>, which has long been the hardest part of | |
| building a new LLVM target. This framework handles a lot of the mundane (but | |
| easy to get wrong) details of writing the instruction selector, such as | |
| generating efficient code for <a | |
| href="LangRef.html#i_getelementptr">getelementptr</a> instructions, promoting | |
| small integer types to larger types (e.g. for RISC targets with one size of | |
| integer registers), expanding 64-bit integer operations for 32-bit targets, etc. | |
| Currently, the X86, PowerPC, Alpha, and IA-64 backends use this framework. The | |
| SPARC backends will be migrated when time permits. | |
| </p> | |
| </div> | |
| <!--_________________________________________________________________________--> | |
| <div class="doc_subsubsection"><a name="customccs">New Support for Per-Function | |
| Calling Conventions</a></div> | |
| <div class="doc_text"> | |
| <p>LLVM 1.5 adds supports for <a href="LangRef.html#callingconv">per-function | |
| calling conventions</a>. Traditionally, the LLVM code generators match the | |
| native C calling conventions for a target. This is important for compatibility, | |
| but is not very flexible. This release allows custom calling conventions to be | |
| established for functions, and defines three target-independent conventions (<a | |
| href="LangRef.html#callingconv">C call, fast call, and cold call</a>) which may | |
| be supported by code generators. When possible, the LLVM optimizer promotes C | |
| functions to use the "fastcc" convention, allowing the use of more efficient | |
| calling sequences (e.g., parameters are passed in registers in the X86 target). | |
| </p> | |
| <p>Targets may now also define target-specific calling conventions, allowing | |
| LLVM to fully support calling convention altering options (e.g. GCC's | |
| <tt>-mregparm</tt> flag) and well-defined target conventions (e.g. stdcall and | |
| fastcall on X86).</p> | |
| </div> | |
| <!--_________________________________________________________________________--> | |
| <div class="doc_subsubsection"><a name="tailcalls">New Support for | |
| Proper Tail Calls</a></div> | |
| <div class="doc_text"> | |
| <p>The release now includes support for <a | |
| href="http://doi.acm.org/10.1145/277650.277719">proper tail calls</a>, as | |
| required to implement languages like Scheme. Tail calls make use of two | |
| features: custom calling conventions (described above), which allow the code | |
| generator to use a convention where the caller deallocates its stack before it | |
| returns. The second feature is a flag on the <a href="LangRef.html#i_call">call | |
| instruction</a>, which indicates that the callee does not access the caller's | |
| stack frame (indicating that it is acceptable to deallocate the caller stack | |
| before invoking the callee). LLVM proper tail calls run on the system stack (as | |
| do normal calls), supports indirect tail calls, tail calls with arbitrary | |
| numbers of arguments, tail calls where the callee requires more argument space | |
| than the caller, etc. The only case not supported are varargs calls, but that | |
| could be added if desired. | |
| </p> | |
| <p>To ensure a call is interpreted as a tail call, a front-end must mark | |
| functions as "fastcc", mark calls with the 'tail' marker, and follow the call | |
| with a return of the called value (or void). The optimizer and code generator | |
| attempt to handle more general cases, but the simple case will always work if | |
| the code generator supports tail calls. Here is an example:</p> | |
| <pre> | |
| fastcc int %bar(int %X, int(double, int)* %FP) { ;<i> fastcc</i> | |
| %Y = tail call fastcc int %FP(double 0.0, int %X) ;<i> tail, fastcc</i> | |
| ret int %Y | |
| } | |
| </pre> | |
| <p>In LLVM 1.5, the X86 code generator is the only target that has been enhanced | |
| to support proper tail calls (other targets will be enhanced in future). | |
| Further, because this support was added very close to the release, it is | |
| disabled by default. Pass <tt>-enable-x86-fastcc</tt> to llc to enable it (this | |
| will be enabled by default in the next release). The example above compiles to: | |
| </p> | |
| <pre> | |
| bar: | |
| sub ESP, 8 # Callee uses more space than the caller | |
| mov ECX, DWORD PTR [ESP + 8] # Get the old return address | |
| mov DWORD PTR [ESP + 4], 0 # First half of 0.0 | |
| mov DWORD PTR [ESP + 8], 0 # Second half of 0.0 | |
| mov DWORD PTR [ESP], ECX # Put the return address where it belongs | |
| jmp EDX # Tail call "FP" | |
| </pre> | |
| <p> | |
| With fastcc on X86, the first two integer arguments are passed in EAX/EDX, the | |
| callee pops its arguments off the stack, and the argument area is always a | |
| multiple of 8 bytes in size. | |
| </p> | |
| </div> | |
| <!--_________________________________________________________________________--> | |
| <div class="doc_subsubsection">Other New Features</div> | |
| <div class="doc_text"> | |
| <ol> | |
| <li>LLVM now includes an <a href="http://llvm.cs.uiuc.edu/PR415"> | |
| Interprocedural Sparse Conditional Constant Propagation</a> pass, named | |
| -ipsccp, which is run by default at link-time.</li> | |
| <li>LLVM 1.5 is now about 15% faster than LLVM 1.4 and its core data | |
| structures use about 30% less memory.</li> | |
| <li>Support for Microsoft Visual Studio is improved, and <a | |
| href="GettingStartedVS.html">now documented</a>. Most LLVM tools build | |
| natively with Visual C++ now.</li> | |
| <li><a href="GettingStarted.html#config">Configuring LLVM to build a subset | |
| of the available targets</a> is now implemented, via the | |
| <tt>--enable-targets=</tt> option.</li> | |
| <li>LLVM can now create native shared libraries with '<tt>llvm-gcc ... | |
| -shared -Wl,-native</tt>' (or with <tt>-Wl,-native-cbe</tt>).</li> | |
| <li>LLVM now supports a new "<a href="LangRef.html#i_prefetch">llvm.prefetch | |
| </a>" intrinsic, and llvm-gcc now supports __builtin_prefetch. | |
| <li>LLVM now supports intrinsics for <a href="LangRef.html#int_count">bit | |
| counting</a> and llvm-gcc now implements the GCC | |
| <tt>__builtin_popcount</tt>, <tt>__builtin_ctz</tt>, and | |
| <tt>__builtin_clz</tt> builtins.</li> | |
| <li>LLVM now mostly builds on HP-UX with the HP aCC Compiler.</li> | |
| <li>The LLVM X86 backend can now emit Cygwin-compatible .s files.</li> | |
| <li>LLVM now includes workarounds in the code generator generator which | |
| reduces the likelyhood of <a href="http://llvm.cs.uiuc.edu/PR448">GCC | |
| hitting swap during optimized builds</a>.</li> | |
| <li>The <a href="http://llvm.cs.uiuc.edu/ProjectsWithLLVM/#llvmtv">LLVM | |
| Transformation Visualizer</a> (llvm-tv) project has been updated to | |
| work with LLVM 1.5.</li> | |
| <li>Nightly tester output is now archived on the <a | |
| href="http://mail.cs.uiuc.edu/pipermail/llvm-testresults/"> | |
| llvm-testresults</a> mailing list.</li> | |
| </ol> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="codequality">Code Quality Improvements in LLVM 1.5</a> | |
| </div> | |
| <div class="doc_text"> | |
| <ol> | |
| <li>The new -simplify-libcalls pass improves code generated for well-known | |
| library calls. The pass optimizes calls to many of the string, memory, and | |
| standard I/O functions (e.g. replace the calls with simpler/faster calls) when | |
| possible, given information known statically about the arguments to the call. | |
| </li> | |
| <li>The -globalopt pass now promotes non-address-taken static globals that are | |
| only accessed in main to SSA registers.</li> | |
| <li>Loops with trip counts based on array pointer comparisons (e.g. "<tt>for (i | |
| = 0; &A[i] != &A[n]; ++i) ...</tt>") are optimized better than before, | |
| which primarily helps iterator-intensive C++ code.</li> | |
| <li>The optimizer now eliminates simple cases where redundant conditions exist | |
| between neighboring blocks.</li> | |
| <li>The reassociation pass (which turns (1+X+3) into (X+1+3) among other | |
| things), is more aggressive and intelligent.</li> | |
| <li>The -prune-eh pass now detects no-return functions in addition to the | |
| no-unwind functions it did before.</li> | |
| <li>The -globalsmodref alias analysis generates more precise results in some | |
| cases.</li> | |
| </ol> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="codequality">Code Generator Improvements in LLVM 1.5</a> | |
| </div> | |
| <div class="doc_text"> | |
| <ol> | |
| <li>The code generator now can provide and use information about commutative | |
| two-address instructions when performing register allocation.</li> | |
| <li>The code generator now tracks function live-in registers explicitly, | |
| instead of requiring the target to generate 'implicit defs' at the | |
| entry to a function.</li> | |
| <li>The code generator can lower integer division by a constant to | |
| multiplication by a magic constant and multiplication by a constant into | |
| shift/add sequences.</li> | |
| <li>The code generator compiles fabs/fneg/sin/cos/sqrt to assembly instructions | |
| when possible.</li> | |
| <li>The PowerPC backend generates better code in many cases, making use of | |
| FMA instructions and the recording ("dot") forms of various PowerPC | |
| instructions.</li> | |
| </ol> | |
| </div> | |
| <!--=========================================================================--> | |
| <div class="doc_subsection"> | |
| <a name="bugfix">Significant Bugs Fixed in LLVM 1.5</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p>Bugs fixed in the LLVM Core:</p> | |
| <ol> | |
| <li><a href="http://llvm.cs.uiuc.edu/PR491">[dse] DSE deletes stores that | |
| are partially overwritten by smaller stores</a></li> | |
| <li><a href="http://llvm.cs.uiuc.edu/PR548">[instcombine] miscompilation of | |
| setcc or setcc in one case</a></li> | |
| <li>Transition code for LLVM 1.0 style varargs was removed from the .ll file | |
| parser. LLVM 1.0 bytecode files are still supported. </li> | |
| </ol> | |
| <p>Code Generator Bugs:</p> | |
| <ol> | |
| <li><a href="http://llvm.cs.uiuc.edu/PR490">[cbackend] Logical constant | |
| expressions (and/or/xor) not implemented</a>.</li> | |
| <li><a href="http://llvm.cs.uiuc.edu/PR511">[cbackend] C backend does not | |
| respect 'volatile'</a>.</li> | |
| <li>The JIT sometimes miscompiled globals and constant pool entries for | |
| 64-bit integer constants on 32-bit hosts.</li> | |
| <li>The C backend should no longer produce code that crashes ICC 8.1.</li> | |
| </ol> | |
| <p>Bugs in the C/C++ front-end:</p> | |
| <ol> | |
| <li><a href="http://llvm.cs.uiuc.edu/PR487">[llvmgcc] llvm-gcc incorrectly | |
| rejects some constant initializers involving the addresses of array | |
| elements</a></li> | |
| <li><a href="http://llvm.cs.uiuc.edu/PR501">[llvm-g++] Crash compiling | |
| anonymous union</a></li> | |
| <li><a href="http://llvm.cs.uiuc.edu/PR509">[llvm-g++] Do not use dynamic | |
| initialization where static init will do</a></li> | |
| <li><a href="http://llvm.cs.uiuc.edu/PR510">[llvmgcc] Field offset | |
| miscalculated for some structure fields following bit fields</a></li> | |
| <li><a href="http://llvm.cs.uiuc.edu/PR513">[llvm-g++] Temporary lifetimes | |
| incorrect for short circuit logical operations</a></li> | |
| <li><a href="http://llvm.cs.uiuc.edu/PR517">[llvm-gcc] Crash compiling | |
| bitfield <-> aggregate assignment</a></li> | |
| <li><a href="http://llvm.cs.uiuc.edu/PR520">[llvm-g++] Error compiling | |
| virtual function thunk with an unnamed argument</a></li> | |
| <li><a href="http://llvm.cs.uiuc.edu/PR522">[llvm-gcc] Crash on certain | |
| C99 complex number routines</a></li> | |
| <li><a href="http://llvm.cs.uiuc.edu/PR529">[llvm-g++] Crash using placement | |
| new on an array type</a></li> | |
| </ol> | |
| </div> | |
| <!-- *********************************************************************** --> | |
| <div class="doc_section"> | |
| <a name="portability">Portability and Supported Platforms</a> | |
| </div> | |
| <!-- *********************************************************************** --> | |
| <div class="doc_text"> | |
| <p>LLVM is known to work on the following platforms:</p> | |
| <ul> | |
| <li>Intel and AMD machines running Red Hat Linux, Fedora Core and FreeBSD | |
| (and probably other unix-like systems).</li> | |
| <li>Sun UltraSPARC workstations running Solaris 8.</li> | |
| <li>Intel and AMD machines running on Win32 with the Cygwin libraries (limited | |
| support is available for native builds with Visual C++).</li> | |
| <li>PowerPC-based Mac OS X systems, running 10.2 and above.</li> | |
| <li>Alpha-based machines running Debian GNU/Linux.</li> | |
| <li>Itanium-based machines running Linux and HP-UX.</li> | |
| </ul> | |
| <p>The core LLVM infrastructure uses | |
| <a href="http://www.gnu.org/software/autoconf/">GNU autoconf</a> to adapt itself | |
| to the machine and operating system on which it is built. However, minor | |
| porting may be required to get LLVM to work on new platforms. We welcome your | |
| portability patches and reports of successful builds or error messages.</p> | |
| </div> | |
| <!-- *********************************************************************** --> | |
| <div class="doc_section"> | |
| <a name="knownproblems">Known Problems</a> | |
| </div> | |
| <!-- *********************************************************************** --> | |
| <div class="doc_text"> | |
| <p>This section contains all known problems with the LLVM system, listed by | |
| component. As new problems are discovered, they will be added to these | |
| sections. If you run into a problem, please check the <a | |
| href="http://llvm.cs.uiuc.edu/bugs/">LLVM bug database</a> and submit a bug if | |
| there isn't already one.</p> | |
| </div> | |
| <!-- ======================================================================= --> | |
| <div class="doc_subsection"> | |
| <a name="experimental">Experimental features included with this release</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p>The following components of this LLVM release are either untested, known to | |
| be broken or unreliable, or are in early development. These components should | |
| not be relied on, and bugs should not be filed against them, but they may be | |
| useful to some people. In particular, if you would like to work on one of these | |
| components, please contact us on the llvmdev list.</p> | |
| <ul> | |
| <li>The following passes are incomplete or buggy, and may be removed in future | |
| releases: <tt>-cee, -branch-combine, -instloops, -paths, -pre</tt></li> | |
| <li>The <tt>llvm-db</tt> tool is in a very early stage of development, but can | |
| be used to step through programs and inspect the stack.</li> | |
| <li>The "iterative scan" register allocator (enabled with | |
| <tt>-regalloc=iterativescan</tt>) is not stable.</li> | |
| <li>The SparcV8, Alpha, and IA64 code generators are experimental.</li> | |
| </ul> | |
| </div> | |
| <!-- ======================================================================= --> | |
| <div class="doc_subsection"> | |
| <a name="core">Known problems with the LLVM Core</a> | |
| </div> | |
| <div class="doc_text"> | |
| <ul> | |
| <li>In the JIT, <tt>dlsym()</tt> on a symbol compiled by the JIT will not | |
| work.</li> | |
| <li>The JIT does not use mutexes to protect its internal data structures. As | |
| such, execution of a threaded program could cause these data structures to be | |
| corrupted. | |
| </li> | |
| <li><a href="http://llvm.cs.uiuc.edu/PR240">The lower-invoke pass does not | |
| mark values live across a setjmp as volatile</a>. This missing feature | |
| only affects targets whose setjmp/longjmp libraries do not save and restore | |
| the entire register file.</li> | |
| </ul> | |
| </div> | |
| <!-- ======================================================================= --> | |
| <div class="doc_subsection"> | |
| <a name="c-fe">Known problems with the C front-end</a> | |
| </div> | |
| <!-- _______________________________________________________________________ --> | |
| <div class="doc_subsubsection">Bugs</div> | |
| <div class="doc_text"> | |
| <ul> | |
| <li>C99 Variable sized arrays do not release stack memory when they go out of | |
| scope. Thus, the following program may run out of stack space: | |
| <pre> | |
| for (i = 0; i != 1000000; ++i) { | |
| int X[n]; | |
| foo(X); | |
| } | |
| </pre></li> | |
| <li>Initialization of global union variables can only be done <a | |
| href="http://llvm.cs.uiuc.edu/PR162">with the largest union member</a>.</li> | |
| </ul> | |
| </div> | |
| <!-- _______________________________________________________________________ --> | |
| <div class="doc_subsubsection"> | |
| Notes | |
| </div> | |
| <div class="doc_text"> | |
| <ul> | |
| <li>Inline assembly is not yet supported.</li> | |
| <li>"long double" is transformed by the front-end into "double". There is no | |
| support for floating point data types of any size other than 32 and 64 | |
| bits.</li> | |
| <li>The following Unix system functionality has not been tested and may not | |
| work: | |
| <ol> | |
| <li><tt>sigsetjmp</tt>, <tt>siglongjmp</tt> - These are not turned into the | |
| appropriate <tt>invoke</tt>/<tt>unwind</tt> instructions. Note that | |
| <tt>setjmp</tt> and <tt>longjmp</tt> <em>are</em> compiled correctly. | |
| <li><tt>getcontext</tt>, <tt>setcontext</tt>, <tt>makecontext</tt> | |
| - These functions have not been tested. | |
| </ol></li> | |
| <li>Although many GCC extensions are supported, some are not. In particular, | |
| the following extensions are known to <b>not be</b> supported: | |
| <ol> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Local-Labels.html#Local%20Labels">Local Labels</a>: Labels local to a block.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Nested-Functions.html#Nested%20Functions">Nested Functions</a>: As in Algol and Pascal, lexical scoping of functions.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Constructing-Calls.html#Constructing%20Calls">Constructing Calls</a>: Dispatching a call to another function.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#Extended%20Asm">Extended Asm</a>: Assembler instructions with C expressions as operands.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Constraints.html#Constraints">Constraints</a>: Constraints for asm operands.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Asm-Labels.html#Asm%20Labels">Asm Labels</a>: Specifying the assembler name to use for a C symbol.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Explicit-Reg-Vars.html#Explicit%20Reg%20Vars">Explicit Reg Vars</a>: Defining variables residing in specified registers.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Vector-Extensions.html#Vector%20Extensions">Vector Extensions</a>: Using vector instructions through built-in functions.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Target-Builtins.html#Target%20Builtins">Target Builtins</a>: Built-in functions specific to particular targets.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Thread_002dLocal.html">Thread-Local</a>: Per-thread variables.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Pragmas.html#Pragmas">Pragmas</a>: Pragmas accepted by GCC.</li> | |
| </ol> | |
| <p>The following GCC extensions are <b>partially</b> supported. An ignored | |
| attribute means that the LLVM compiler ignores the presence of the attribute, | |
| but the code should still work. An unsupported attribute is one which is | |
| ignored by the LLVM compiler and will cause a different interpretation of | |
| the program.</p> | |
| <ol> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html#Variable%20Length">Variable Length</a>: | |
| Arrays whose length is computed at run time.<br> | |
| Supported, but allocated stack space is not freed until the function returns (noted above).</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html#Function%20Attributes">Function Attributes</a>: | |
| Declaring that functions have no side effects or that they can never | |
| return.<br> | |
| <b>Supported:</b> <tt>format</tt>, <tt>format_arg</tt>, <tt>non_null</tt>, | |
| <tt>noreturn</tt>, <tt>constructor</tt>, <tt>destructor</tt>, | |
| <tt>unused</tt>, | |
| <tt>deprecated</tt>, <tt>warn_unused_result</tt>, <tt>weak</tt><br> | |
| <b>Ignored:</b> <tt>noinline</tt>, | |
| <tt>always_inline</tt>, <tt>pure</tt>, <tt>const</tt>, <tt>nothrow</tt>, | |
| <tt>malloc</tt>, <tt>no_instrument_function</tt>, <tt>cdecl</tt><br> | |
| <b>Unsupported:</b> <tt>used</tt>, <tt>section</tt>, <tt>alias</tt>, | |
| <tt>visibility</tt>, <tt>regparm</tt>, <tt>stdcall</tt>, | |
| <tt>fastcall</tt>, all other target specific attributes</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variable-Attributes.html#Variable%20Attributes">Variable Attributes</a>: | |
| Specifying attributes of variables.<br> | |
| <b>Supported:</b> <tt>cleanup</tt>, <tt>common</tt>, <tt>nocommon</tt>, | |
| <tt>deprecated</tt>, <tt>transparent_union</tt>, | |
| <tt>unused</tt>, <tt>weak</tt><br> | |
| <b>Unsupported:</b> <tt>aligned</tt>, <tt>mode</tt>, <tt>packed</tt>, | |
| <tt>section</tt>, <tt>shared</tt>, <tt>tls_model</tt>, | |
| <tt>vector_size</tt>, <tt>dllimport</tt>, | |
| <tt>dllexport</tt>, all target specific attributes.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Type-Attributes.html#Type%20Attributes">Type Attributes</a>: Specifying attributes of types.<br> | |
| <b>Supported:</b> <tt>transparent_union</tt>, <tt>unused</tt>, | |
| <tt>deprecated</tt>, <tt>may_alias</tt><br> | |
| <b>Unsupported:</b> <tt>aligned</tt>, <tt>packed</tt>, | |
| all target specific attributes.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#Other%20Builtins">Other Builtins</a>: | |
| Other built-in functions.<br> | |
| We support all builtins which have a C language equivalent (e.g., | |
| <tt>__builtin_cos</tt>), <tt>__builtin_alloca</tt>, | |
| <tt>__builtin_types_compatible_p</tt>, <tt>__builtin_choose_expr</tt>, | |
| <tt>__builtin_constant_p</tt>, and <tt>__builtin_expect</tt> | |
| (currently ignored). We also support builtins for ISO C99 floating | |
| point comparison macros (e.g., <tt>__builtin_islessequal</tt>), | |
| <tt>__builtin_prefetch</tt>, <tt>__builtin_popcount[ll]</tt>, | |
| <tt>__builtin_clz[ll]</tt>, and <tt>__builtin_ctz[ll]</tt>.</li> | |
| </ol> | |
| <p>The following extensions <b>are</b> known to be supported:</p> | |
| <ol> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Labels-as-Values.html#Labels%20as%20Values">Labels as Values</a>: Getting pointers to labels and computed gotos.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html#Statement%20Exprs">Statement Exprs</a>: Putting statements and declarations inside expressions.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Typeof.html#Typeof">Typeof</a>: <code>typeof</code>: referring to the type of an expression.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc-3.4.0/gcc/Lvalues.html#Lvalues">Lvalues</a>: Using <code>?:</code>, "<code>,</code>" and casts in lvalues.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Conditionals.html#Conditionals">Conditionals</a>: Omitting the middle operand of a <code>?:</code> expression.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Long-Long.html#Long%20Long">Long Long</a>: Double-word integers.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Complex.html#Complex">Complex</a>: Data types for complex numbers.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Hex-Floats.html#Hex%20Floats">Hex Floats</a>:Hexadecimal floating-point constants.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html#Zero%20Length">Zero Length</a>: Zero-length arrays.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Empty-Structures.html#Empty%20Structures">Empty Structures</a>: Structures with no members.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Variadic-Macros.html#Variadic%20Macros">Variadic Macros</a>: Macros with a variable number of arguments.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Escaped-Newlines.html#Escaped%20Newlines">Escaped Newlines</a>: Slightly looser rules for escaped newlines.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Subscripting.html#Subscripting">Subscripting</a>: Any array can be subscripted, even if not an lvalue.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Pointer-Arith.html#Pointer%20Arith">Pointer Arith</a>: Arithmetic on <code>void</code>-pointers and function pointers.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Initializers.html#Initializers">Initializers</a>: Non-constant initializers.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Compound-Literals.html#Compound%20Literals">Compound Literals</a>: Compound literals give structures, unions, | |
| or arrays as values.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html#Designated%20Inits">Designated Inits</a>: Labeling elements of initializers.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Cast-to-Union.html#Cast%20to%20Union">Cast to Union</a>: Casting to union type from any member of the union.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Case-Ranges.html#Case%20Ranges">Case Ranges</a>: `case 1 ... 9' and such.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Mixed-Declarations.html#Mixed%20Declarations">Mixed Declarations</a>: Mixing declarations and code.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Prototypes.html#Function%20Prototypes">Function Prototypes</a>: Prototype declarations and old-style definitions.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/C_002b_002b-Comments.html#C_002b_002b-Comments">C++ Comments</a>: C++ comments are recognized.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Dollar-Signs.html#Dollar%20Signs">Dollar Signs</a>: Dollar sign is allowed in identifiers.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Character-Escapes.html#Character%20Escapes">Character Escapes</a>: <code>\e</code> stands for the character <ESC>.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Alignment.html#Alignment">Alignment</a>: Inquiring about the alignment of a type or variable.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Inline.html#Inline">Inline</a>: Defining inline functions (as fast as macros).</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Alternate-Keywords.html#Alternate%20Keywords">Alternate Keywords</a>:<code>__const__</code>, <code>__asm__</code>, etc., for header files.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Incomplete-Enums.html#Incomplete%20Enums">Incomplete Enums</a>: <code>enum foo;</code>, with details to follow.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Function-Names.html#Function%20Names">Function Names</a>: Printable strings which are the name of the current function.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Return-Address.html#Return%20Address">Return Address</a>: Getting the return or frame address of a function.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Unnamed-Fields.html#Unnamed%20Fields">Unnamed Fields</a>: Unnamed struct/union fields within structs/unions.</li> | |
| <li><a href="http://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html#Attribute%20Syntax">Attribute Syntax</a>: Formal syntax for attributes.</li> | |
| </ol></li> | |
| </ul> | |
| <p>If you run into GCC extensions which have not been included in any of these | |
| lists, please let us know (also including whether or not they work).</p> | |
| </div> | |
| <!-- ======================================================================= --> | |
| <div class="doc_subsection"> | |
| <a name="c++-fe">Known problems with the C++ front-end</a> | |
| </div> | |
| <div class="doc_text"> | |
| <p>For this release, the C++ front-end is considered to be fully | |
| tested and works for a number of non-trivial programs, including LLVM | |
| itself.</p> | |
| </div> | |
| <!-- _______________________________________________________________________ --> | |
| <div class="doc_subsubsection">Bugs</div> | |
| <div class="doc_text"> | |
| <ul> | |
| <li>The C++ front-end inherits all problems afflicting the <a href="#c-fe">C | |
| front-end</a>.</li> | |
| </ul> | |
| </div> | |
| <!-- _______________________________________________________________________ --> | |
| <div class="doc_subsubsection"> | |
| Notes | |
| </div> | |
| <div class="doc_text"> | |
| <ul> | |
| <li>The C++ front-end is based on a pre-release of the GCC 3.4 C++ parser. This | |
| parser is significantly more standards compliant (and picky) than prior GCC | |
| versions. For more information, see the C++ section of the <a | |
| href="http://gcc.gnu.org/gcc-3.4/changes.html">GCC 3.4 release notes</a>.</li> | |
| <li>Destructors for local objects are not always run when a <tt>longjmp</tt> is | |
| performed. In particular, destructors for objects in the <tt>longjmp</tt>ing | |
| function and in the <tt>setjmp</tt> receiver function may not be run. | |
| Objects in intervening stack frames will be destroyed, however (which is | |
| better than most compilers).</li> | |
| <li>The LLVM C++ front-end follows the <a | |
| href="http://www.codesourcery.com/cxx-abi">Itanium C++ ABI</a>. | |
| This document, which is not Itanium specific, specifies a standard for name | |
| mangling, class layout, v-table layout, RTTI formats, and other C++ | |
| representation issues. Because we use this API, code generated by the LLVM | |
| compilers should be binary compatible with machine code generated by other | |
| Itanium ABI C++ compilers (such as G++, the Intel and HP compilers, etc). | |
| <i>However</i>, the exception handling mechanism used by LLVM is very | |
| different from the model used in the Itanium ABI, so <b>exceptions will not | |
| interact correctly</b>. </li> | |
| </ul> | |
| </div> | |
| <!-- ======================================================================= --> | |
| <div class="doc_subsection"> | |
| <a name="c-be">Known problems with the C back-end</a> | |
| </div> | |
| <div class="doc_text"> | |
| <ul> | |
| <li>The C back-end produces code that violates the ANSI C Type-Based Alias | |
| Analysis rules. As such, special options may be necessary to compile the code | |
| (for example, GCC requires the <tt>-fno-strict-aliasing</tt> option). This | |
| problem probably cannot be fixed.</li> | |
| <li><a href="http://llvm.cs.uiuc.edu/PR56">Zero arg vararg functions are not | |
| supported</a>. This should not affect LLVM produced by the C or C++ | |
| frontends.</li> | |
| </ul> | |
| </div> | |
| <!-- ======================================================================= --> | |
| <div class="doc_subsection"> | |
| <a name="x86-be">Known problems with the X86 back-end</a> | |
| </div> | |
| <div class="doc_text"> | |
| <ul> | |
| <li><a href="http://llvm.cs.uiuc.edu/PR566">Memory Mapped I/O Intrinsics do not fence memory</a></li> | |
| </ul> | |
| </div> | |
| <!-- ======================================================================= --> | |
| <div class="doc_subsection"> | |
| <a name="ppc-be">Known problems with the PowerPC back-end</a> | |
| </div> | |
| <div class="doc_text"> | |
| <ul> | |
| <li>None yet</li> | |
| </ul> | |
| </div> | |
| <!-- ======================================================================= --> | |
| <div class="doc_subsection"> | |
| <a name="sparcv9-be">Known problems with the SparcV9 back-end</a> | |
| </div> | |
| <div class="doc_text"> | |
| <ul> | |
| <li><a href="http://llvm.cs.uiuc.edu/PR60">[sparcv9] SparcV9 backend miscompiles | |
| several programs in the LLVM test suite</a></li> | |
| </ul> | |
| </div> | |
| <!-- ======================================================================= --> | |
| <div class="doc_subsection"> | |
| <a name="alpha-be">Known problems with the Alpha back-end</a> | |
| </div> | |
| <div class="doc_text"> | |
| <ul> | |
| <li>On 21164s, some rare FP arithmetic sequences which may trap do not have the | |
| appropriate nops inserted to ensure restartability.</li> | |
| <li>Defining vararg functions is not supported (but calling them is ok).</li> | |
| <li>Due to the vararg problems, C++ exceptions do not work. Small changes are required to the CFE (which break correctness in the exception handler) to compile the exception handling library (and thus the C++ standard library).</li> | |
| </ul> | |
| </div> | |
| <!-- ======================================================================= --> | |
| <div class="doc_subsection"> | |
| <a name="ia64-be">Known problems with the IA64 back-end</a> | |
| </div> | |
| <div class="doc_text"> | |
| <ul> | |
| <li>C++ programs are likely to fail on IA64, as calls to <tt>setjmp</tt> are | |
| made where the argument is not 16-byte aligned, as required on IA64. (Strictly | |
| speaking this is not a bug in the IA64 back-end; it will also be encountered | |
| when building C++ programs using the C back-end.)</li> | |
| <li>The C++ front-end does not use <a href="http://llvm.cs.uiuc.edu/PR406">IA64 | |
| ABI compliant layout of v-tables</a>. In particular, it just stores function | |
| pointers instead of function descriptors in the vtable. This bug prevents | |
| mixing C++ code compiled with LLVM with C++ objects compiled by other C++ | |
| compilers.</li> | |
| <li>There are a few ABI violations which will lead to problems when mixing LLVM | |
| output with code built with other compilers, particularly for floating-point | |
| programs.</li> | |
| <li>Defining vararg functions is not supported (but calling them is ok).</li> | |
| </ul> | |
| </div> | |
| <!-- ======================================================================= --> | |
| <div class="doc_subsection"> | |
| <a name="sparcv8">Known problems with the SPARC-V8 back-end</a> | |
| </div> | |
| <div class="doc_text"> | |
| <ul> | |
| <li>Many features are still missing (e.g. support for 64-bit integer | |
| arithmetic).</li> | |
| <li>This backend needs to be updated to use the SelectionDAG instruction | |
| selection framework.</li> | |
| </ul> | |
| </div> | |
| <!-- *********************************************************************** --> | |
| <div class="doc_section"> | |
| <a name="additionalinfo">Additional Information</a> | |
| </div> | |
| <!-- *********************************************************************** --> | |
| <div class="doc_text"> | |
| <p>A wide variety of additional information is available on the <a | |
| href="http://llvm.cs.uiuc.edu">LLVM web page</a>, including <a | |
| href="http://llvm.cs.uiuc.edu/docs/">documentation</a> and <a | |
| href="http://llvm.cs.uiuc.edu/pubs/">publications describing algorithms and | |
| components implemented in LLVM</a>. The web page also contains versions of the | |
| API documentation which is up-to-date with the CVS version of the source code. | |
| You can access versions of these documents specific to this release by going | |
| into the "<tt>llvm/doc/</tt>" directory in the LLVM tree.</p> | |
| <p>If you have any questions or comments about LLVM, please feel free to contact | |
| us via the <a href="http://llvm.cs.uiuc.edu/docs/#maillist"> mailing | |
| lists</a>.</p> | |
| </div> | |
| <!-- *********************************************************************** --> | |
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