standardize on <tt>FOOCLASS::Create</tt> for all IR classes in the future,
but not all of them have been moved over yet.</li>
<li>LLVM 2.3 renames the LLVMBuilder and LLVMFoldingBuilder classes to
- IRBuilder.</li>
-<li>MRegisterInfo was renamed to TargetRegisterInfo.</li>
-<li>The MappedFile class is gone, please use MemoryBuffer instead.</li>
+ <a href="http://llvm.org/doxygen/classllvm_1_1IRBuilder.html">IRBuilder</a>.
+ </li>
+<li>MRegisterInfo was renamed to
+ <a href="http://llvm.org/doxygen/classllvm_1_1TargetRegisterInfo.html">
+ TargetRegisterInfo</a>.</li>
+<li>The MappedFile class is gone, please use
+ <a href="http://llvm.org/doxygen/classllvm_1_1MemoryBuffer.html">
+ MemoryBuffer</a> instead.</li>
<li>The '<tt>-enable-eh</tt>' flag to llc has been removed. Now code should
encode whether it is safe to omit unwind information for a function by
tagging the Function object with the '<tt>nounwind</tt>' attribute.</li>
+<li>The ConstantFP::get method that uses APFloat now takes one argument
+ instead of two. The type argument has been removed, and the type is
+ now inferred from the size of the given APFloat value.</li>
</ul>
</div>
downloaded from:
</p>
-<p>
-<tt>svn co http://llvm.org/svn/llvm-project/vmkit/trunk vmkit</tt>
-</p>
+<div class="doc_code">
+<pre>svn co http://llvm.org/svn/llvm-project/vmkit/trunk vmkit</pre>
+</div>
</div>
transformations (such as refactoring) and other source-level tools for C and
Objective-C. Clang now also includes tools for turning C code into pretty HTML,
and includes a new <a href="http://clang.llvm.org/StaticAnalysis.html">static
-analysis tool</a> in development. This tool is automatically focused on finding
+analysis tool</a> in development. This tool focuses on automatically finding
bugs in C and Objective-C code.</p>
</div>
</div>
<!-- *********************************************************************** -->
+<div class="doc_text">
+
+<p>LLVM 2.3 includes a huge number of bug fixes, performance tweaks and minor
+improvements. Some of the major improvements and new features are listed in
+this section.
+</p>
+</div>
+
<!--=========================================================================-->
<div class="doc_subsection">
<a name="majorfeatures">Major New Features</a>
<tt>llvmc</tt> and to provide a superset of the features of the
'<tt>gcc</tt>' driver.</p>
-<p>The main features of <tt>llvmc2</tt> are:
+
<p>The main features of <tt>llvmc2</tt> are:
<ul>
<li>Extended handling of command line options and smart rules for
dispatching them to different tools.</li>
it's relatively easy to add new features.</li>
<li>The definition of driver is transformed into set of C++ classes, thus
no runtime interpretation is needed.</li>
- </ul></p>
- </li>
+ </ul>
+</li>
<li><p>LLVM 2.3 includes a completely rewritten interface for <a
href="LinkTimeOptimization.html">Link Time Optimization</a>. This interface
<div class="doc_text">
-<p>LLVM 2.3 fully supports the llvm-gcc 4.2 front-end.</p>
+<p>LLVM 2.3 fully supports the llvm-gcc 4.2 front-end, and includes support
+for the C, C++, Objective-C, Ada, and Fortran front-ends.</p>
-<p>llvm-gcc 4.2 includes numerous fixes to better support the Objective-C
-front-end. Objective-C now works very well on Mac OS/X.</p>
+<p>
+<ul>
+<li>llvm-gcc 4.2 includes numerous fixes to better support the Objective-C
+front-end. Objective-C now works very well on Mac OS/X.</li>
-<p>Fortran EQUIVALENCEs are now supported by the gfortran front-end.</p>
+<li>Fortran <tt>EQUIVALENCE</tt>s are now supported by the gfortran
+front-end.</li>
-<p>llvm-gcc 4.2 includes many other fixes which improve conformance with the
-relevant parts of the GCC testsuite.</p>
+<li>llvm-gcc 4.2 includes many other fixes which improve conformance with the
+relevant parts of the GCC testsuite.</li>
+
+</ul>
</div>
<p>New features include:
</p>
+<ul>
+<li>LLVM IR now directly represents "common" linkage, instead of representing it
+as a form of weak linkage.</li>
-Common linkage?
-
-Atomic operation support, Alpha, X86, X86-64, PowerPC. "__sync_synchronize",
-"__sync_val_compare_and_swap", etc
+<li>LLVM IR now has support for atomic operations, and this functionality can be
+accessed through the llvm-gcc "<tt>__sync_synchronize</tt>",
+"<tt>__sync_val_compare_and_swap</tt>", and related builtins. Support for
+atomics are available in the Alpha, X86, X86-64, and PowerPC backends.</li>
-<ul>
-<li>The C and Ocaml bindings have received additional improvements. The
-bindings now cover pass managers, several transformation passes, iteration
-over the LLVM IR, target data, and parameter attribute lists.</li>
+<li>The C and Ocaml bindings have extended to cover pass managers, several
+transformation passes, iteration over the LLVM IR, target data, and parameter
+attribute lists.</li>
</ul>
</div>
<ul>
-<li>Loop index set splitting on by default.<p>
-This transformation hoists conditions from loop bodies and reduces loop's
-iteration space to improve performance. For example, <p>
+<li><p>Loop index set splitting on by default.
+This transformation hoists conditions from loop bodies and reduces a loop's
+iteration space to improve performance. For example,</p>
+
+<div class="doc_code">
<pre>
for (i = LB; i < UB; ++i)
if (i <= NV)
LOOP_BODY
</pre>
-is transformed into
+</div>
+
+<p>is transformed into:</p>
+
+<p><div class="doc_code">
<pre>
NUB = min(NV+1, UB)
for (i = LB; i < NUB; ++i)
LOOP_BODY
</pre>
+</div>
+</p>
</li>
-<li>LLVM includes a new <tt>memcpy</tt> optimization pass which removes
+<li>LLVM now includes a new <tt>memcpy</tt> optimization pass which removes
dead <tt>memcpy</tt> calls, unneeded copies of aggregates, and performs
return slot optimization. The LLVM optimizer now notices long sequences of
consecutive stores and merges them into <tt>memcpy</tt>'s where profitable.</li>
<li>Alignment detection for vector memory references and for <tt>memcpy</tt> and
<tt>memset</tt> is now more aggressive.</li>
-<li>The aggressive dead code elimination (ADCE) optimization has been rewritten
+<li>The Aggressive Dead Code Elimination (ADCE) optimization has been rewritten
to make it both faster and safer in the presence of code containing infinite
loops. Some of its prior functionality has been factored out into the loop
-deletion pass, which <em>is</em> safe for infinite loops.</li>
+deletion pass, which <em>is</em> safe for infinite loops. The new ADCE pass is
+no longer based on control dependence, making it run faster.</li>
-<li>Several optimizations have been sped up, leading to faster code generation
- with the same code quality.</li>
-
<li>The 'SimplifyLibCalls' pass, which optimizes calls to libc and libm
functions for C-based languages, has been rewritten to be a FunctionPass
instead a ModulePass. This allows it to be run more often and to be
<li>Several corner case bugs which could lead to deleting volatile memory
accesses have been fixed.</li>
+
+<li>Several optimizations have been sped up, leading to faster code generation
+ with the same code quality.</li>
+
</ul>
</div>
faster:</p>
<ul>
-<li>MemOperand in the code generator: describe me!.</li>
-
-<li>The target-independent code generator infrastructure now uses LLVM's APInt
+<li>The code generator now has support for carrying information about memory
+ references throughout the entire code generation process, via the
+ <a href="http://llvm.org/doxygen/classllvm_1_1MachineMemOperand.html">
+ MachineMemOperand</a> class. In the future this will be used to improve
+ both pre-pass and post-pass scheduling, and to improve compiler-debugging
+ output.</li>
+
+<li>The target-independent code generator infrastructure now uses LLVM's
+ <a href="http://llvm.org/doxygen/classllvm_1_1APInt.html">APInt</a>
class to handle integer values, which allows it to support integer types
- larger than 64 bits. Note that support for such types is also dependent on
- target-specific support. Use of APInt is also a step toward support for
- non-power-of-2 integer sizes.</li>
+ larger than 64 bits (for example i128). Note that support for such types is
+ also dependent on target-specific support. Use of APInt is also a step
+ toward support for non-power-of-2 integer sizes.</li>
<li>LLVM 2.3 includes several compile time speedups for code with large basic
blocks, particularly in the instruction selection phase, register
allocation, scheduling, and tail merging/jump threading.</li>
-<li>Several improvements which make llc's <tt>--view-sunit-dags</tt>
- visualization of scheduling dependency graphs easier to understand.</li>
+<li>LLVM 2.3 includes several improvements which make llc's
+ <tt>--view-sunit-dags</tt> visualization of scheduling dependency graphs
+ easier to understand.</li>
<li>The code generator allows targets to write patterns that generate subreg
references directly in .td files now.</li>
'i' form when possible instead of always loading the value in a register.
This saves an instruction and reduces register use.</li>
-<li>Added support for PIC/GOT style tail calls on x86/32 and initial support
- for tail calls on PowerPC 32 (it may also work on ppc64 but not
- thoroughly tested).</li>
+<li>Added support for PIC/GOT style <a
+ href="CodeGenerator.html#tailcallopt">tail calls</a> on X86/32 and initial
+ support for tail calls on PowerPC 32 (it may also work on PowerPC 64 but is
+ not thoroughly tested).</li>
</ul>
</div>
now interoperates very well on X86-64 systems with other compilers.</li>
<li>Support for Win64 was added. This includes code generation itself, JIT
- support and necessary changes to llvm-gcc.</li>
+ support, and necessary changes to llvm-gcc.</li>
<li>The LLVM X86 backend now supports the support SSE 4.1 instruction set, and
the llvm-gcc 4.2 front-end supports the SSE 4.1 compiler builtins. Various
<li>The X86 backend now does a number of optimizations that aim to avoid
converting numbers back and forth from SSE registers to the X87 floating
- point stack.</li>
+ point stack. This is important because most X86 ABIs require return values
+ to be on the X87 Floating Point stack, but most CPUs prefer computation in
+ the SSE units.</li>
<li>The X86 backend supports stack realignment, which is particularly useful for
- vector code on OS's without 16-byte aligned stacks.</li>
+ vector code on OS's without 16-byte aligned stacks, such as Linux and
+ Windows.</li>
<li>The X86 backend now supports the "sseregparm" options in GCC, which allow
functions to be tagged as passing floating point values in SSE
<li><tt>__builtin_prefetch</tt> is now compiled into the appropriate prefetch
instructions instead of being ignored.</li>
-<li>128-bit integers are now supported on X86-64 targets.</li>
+<li>128-bit integers are now supported on X86-64 targets. This can be used
+ through <tt>__attribute__((TImode))</tt> in llvm-gcc.</li>
-<li>The register allocator can now rematerialize PIC-base computations.</li>
+<li>The register allocator can now rematerialize PIC-base computations, which is
+ an important optimization for register use.</li>
<li>The "t" and "f" inline assembly constraints for the X87 floating point stack
now work. However, the "u" constraint is still not fully supported.</li>
<ul>
<li>The LLVM C backend now supports vector code.</li>
+<li>The Cell SPU backend includes a number of improvements. It generates better
+ code and its stability/completeness is improving.</li>
</ul>
</div>
expect small issues to happen. Also, llvm-gcc cannot build mingw64 runtime
currently due
to <a href="http://llvm.org/PR2255">several</a>
- <a href="http://llvm.org/PR2257">bugs</a> in FP stackifier
+ <a href="http://llvm.org/PR2257">bugs</a> due to lack of support for the
+ 'u' inline assembly constraint and X87 floating point inline assembly.</li>
+ <li>The X86-64 backend does not yet support position-independent code (PIC)
+ generation on Linux targets.</li>
+ <li>The X86-64 backend does not yet support the LLVM IR instruction
+ <tt>va_arg</tt>. Currently, the llvm-gcc front-end supports variadic
+ argument constructs on X86-64 by lowering them manually.</li>
</ul>
</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.org/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>
-
-<li>The Itanium backend has bitrotted somewhat.</li>
+<li>The Itanium backend is highly experimental, and has a number of known
+ issues. We are looking for a maintainer for the Itanium backend. If you
+ are interested, please contact the llvmdev mailing list.</li>
</ul>
</div>
<a name="c-fe">Known problems with the llvm-gcc C front-end</a>
</div>
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection">Bugs</div>
-
<div class="doc_text">
<p>llvm-gcc does not currently support <a href="http://llvm.org/PR869">Link-Time
projects / oota-llvm.git / blobdiff