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llvm-svn: 52100
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Chris Lattner
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@ -79,33 +79,59 @@ It includes a large number of features and refinements from LLVM 2.2.</p>
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<div class="doc_text">
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<p>LLVM 2.2 was the last LLVM release to support llvm-gcc 4.0 and llvm-upgrade.
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llvm-gcc 4.0 has been replaced with llvm-gcc 4.2. llvm-upgrade was useful for
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upgrading LLVM 1.9 files to LLVM 2.x syntax, but you can always use a previous
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LLVM release to do this. One nice impact of this is that the LLVM regression
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test suite no longer depends on llvm-upgrade, which makes it run faster.</p>
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<p>LLVM 2.3 no longer supports llvm-gcc 4.0, it has been replaced with
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llvm-gcc 4.2.</p>
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<p><tt>llvm2cpp</tt> tool has been folded into llc, use
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<p>LLVM 2.3 no longer includes the <tt>llvm-upgrade</tt> tool. It was useful
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for upgrading LLVM 1.9 files to LLVM 2.x syntax, but you can always use a
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previous LLVM release to do this. One nice impact of this is that the LLVM
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regression test suite no longer depends on llvm-upgrade, which makes it run
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faster.</p>
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<p>The <tt>llvm2cpp</tt> tool has been folded into llc, use
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<tt>llc -march=cpp</tt> instead of <tt>llvm2cpp</tt>.</p>
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<p>LLVM API Changes:</p>
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<ul>
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<li>Several core LLVM IR classes have migrated to use 'FOOCLASS::Create(...)'
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instead of 'new FOOCLASS(...)' (e.g. where FOOCLASS=BasicBlock). We hope to
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standardize on FOOCLASS::Create for all IR classes in the future, but not
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all of them have been moved over yet.</li>
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<li>Several core LLVM IR classes have migrated to use the
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'<tt>FOOCLASS::Create(...)</tt>' pattern instead of '<tt>new
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FOOCLASS(...)</tt>' (e.g. where FOOCLASS=<tt>BasicBlock</tt>). We hope to
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standardize on <tt>FOOCLASS::Create</tt> for all IR classes in the future,
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but not all of them have been moved over yet.</li>
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<li>LLVM 2.3 renames the LLVMBuilder and LLVMFoldingBuilder classes to
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IRBuilder.</li>
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<li>MRegisterInfo was renamed to TargetRegisterInfo.</li>
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<li>The MappedFile class is gone, please use MemoryBuffer instead.</li>
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<li>The '-enable-eh' flag to llc has been removed. Now code should encode
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whether it is safe to not generate unwind information for a function by
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tagging the Function object with the 'nounwind' attribute.</li>
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<li>The '<tt>-enable-eh</tt>' flag to llc has been removed. Now code should
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encode whether it is safe to omit unwind information for a function by
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tagging the Function object with the '<tt>nounwind</tt>' attribute.</li>
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</ul>
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</div>
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<!--=========================================================================-->
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<div class="doc_subsection">
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<a name="otherprojects">Other LLVM Sub-Projects</a>
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</div>
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<div class="doc_text">
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<p>
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<p>The <a href="http://clang.llvm.org/">clang project</a> is an effort to build
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a set of new 'llvm native' front-end technologies for the LLVM optimizer
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and code generator. Currently, its C and Objective-C support is maturing
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nicely, and it has advanced source-to-source analysis and transformation
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capabilities. If you are interested in building source-level tools for C and
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Objective-C (and eventually C++), you should take a look. However, note that
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clang is not an official part of the LLVM 2.3 release. If you are interested in
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this project, please see its <a href="http://clang.llvm.org/">web site</a>.</p>
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</p>
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</div>
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<!--=========================================================================-->
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<div class="doc_subsection">
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<a name="majorfeatures">Major New Features</a>
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@ -116,34 +142,51 @@ test suite no longer depends on llvm-upgrade, which makes it run faster.</p>
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<p>LLVM 2.3 includes several major new capabilities:</p>
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<ul>
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<li>Multiple Return Value Support.</li>
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<li><p>The biggest change in LLVM 2.3 is Multiple Return Value (MRV) support.
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MRVs allow LLVM IR to directly represent functions that return multiple
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values without having to pass them "by reference" in the LLVM IR. This
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allows a front-end to generate more efficient code, as MRVs are generally
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returned in registers if a target supports them. See the <a
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href="LangRef.html#i_getresult">LLVM IR Reference</a> for more details.</p>
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<p>MRVs are fully supported in the LLVM IR, but are not yet fully supported in
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on all targets. However, it is generally safe to return up to 2 values from
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a function: most targets should be able to handle at least that. MRV
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support is a critical requirement for X86-64 ABI support, as X86-64 requires
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the ability to return multiple registers from functions, and we use MRVs to
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accomplish this in a direct way.</p></li>
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<li><p>LLVM 2.3 includes a complete reimplementation of the "llvmc" tool. It is
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designed to overcome several problems with the original llvmc and to provide a
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superset of the features of the 'gcc' driver.</p>
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<li><p>LLVM 2.3 includes a complete reimplementation of the "<tt>llvmc</tt>"
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tool. It is designed to overcome several problems with the original
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<tt>llvmc</tt> and to provide a superset of the features of the
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'<tt>gcc</tt>' driver.</p>
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<p>The main features of llvmc2 is:</p>
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<ul>
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<li>Extended handling of command line options and smart rules for
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dispatching them to different tools.</li>
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<li>Flexible (and extensible) rules for defining different tools.</li>
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<li>The different intermediate steps performed by tools are represented
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as edges in the abstract graph.</li>
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<li>The 'language' for driver behavior definition is tablegen and thus
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it's relatively easy to add new features.</li>
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<li>The definition of driver is transformed into set of C++ classes, thus
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no runtime interpretation is needed.</li>
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</ul>
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</li>
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<p>The main features of <tt>llvmc2</tt> are:
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<ul>
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<li>Extended handling of command line options and smart rules for
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dispatching them to different tools.</li>
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<li>Flexible (and extensible) rules for defining different tools.</li>
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<li>The different intermediate steps performed by tools are represented
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as edges in the abstract graph.</li>
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<li>The 'language' for driver behavior definition is tablegen and thus
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it's relatively easy to add new features.</li>
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<li>The definition of driver is transformed into set of C++ classes, thus
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no runtime interpretation is needed.</li>
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</ul></p>
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</li>
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<li>Reimplemented <a href="LinkTimeOptimization.html">LTO interface</a> in
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C.</li>
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<li><p>LLVM 2.3 includes a completely rewritten interface for <a
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href="LinkTimeOptimization.html">Link Time Optimization</a>. This interface
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is written in C, which allows for easier integration with C code bases, and
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incorporates improvements we learned about from the first incarnation of the
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interface.</p></li>
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<li>Kaleidoscope tutorial in Ocaml.</li>
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<li><p>The <a href="tutorial/LangImpl1.html">Kaleidoscope tutorial</a> now
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includes a "port" of the tutorial that <a
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href="tutorial/OCamlLangImpl1.html">uses the Ocaml bindings</a> to implement
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the Kaleidoscope language.</p></li>
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</ul>
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@ -152,7 +195,7 @@ no runtime interpretation is needed.</li>
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<!--=========================================================================-->
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<div class="doc_subsection">
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<a name="frontends">llvm-gcc 4.2 Improvements and Clang</a>
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<a name="llvm-gcc">llvm-gcc 4.2 Improvements</a>
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</div>
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<div class="doc_text">
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@ -165,15 +208,6 @@ front-end. Objective-C now works very well on Mac OS/X.</p>
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<p>llvm-gcc 4.2 includes many other fixes which improve conformance with the
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relevant parts of the GCC testsuite.</p>
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<p>The <a href="http://clang.llvm.org/">clang project</a> is an effort to build
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a set of new 'llvm native' front-end technologies for the LLVM optimizer
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and code generator. Currently, its C and Objective-C support is maturing
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nicely, and it has advanced source-to-source analysis and transformation
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capabilities. If you are interested in building source-level tools for C and
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Objective-C (and eventually C++), you should take a look. However, note that
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clang is not an official part of the LLVM 2.3 release. If you are interested in
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this project, please see its <a href="http://clang.llvm.org/">web site</a>.</p>
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</div>
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