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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@128990 91177308-0d34-0410-b5e6-96231b3b80d8
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Chris Lattner 2011-04-06 05:50:04 +00:00
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@ -399,25 +399,21 @@ in this section.
<ul>
<li>
TBAA: On by default in clang. Disable it with -fno-strict-aliasing.
Could be more aggressive for structs.
<li>Type Based Alias Analysis (TBAA) is now implemented and turned on by default
in Clang. This allows substantially better load/store optimization in some
cases. TBAA can be disabled by passing -fno-strict-aliasing.
</li>
<li>New Nvidia PTX backend, not generally useful in 2.9 though.</li>
<li>This release has seen a continued focus on quality of debug information.
LLVM now generates much higher fidelity debug information, particularly when
debugging optimized code.</li>
<li>Inline assembly now supports multiple alternative constraints.</li>
<li>A new backend for the NVIDIA PTX virtual ISA (used to target its GPUs) is
under rapid development. It is not generally useful in 2.9, but is making
rapid progress.</li>
<li>
Much better debug info generated, particularly in optimized code situations.
</li>
<li>
inline asm multiple alternative constraint support.
</li>
<li>
New naming rules in coding standards: CodingStandards.html#ll_naming
</li>
</ul>
</div>
@ -432,13 +428,19 @@ inline asm multiple alternative constraint support.
expose new optimization opportunities:</p>
<ul>
<li>udiv, ashr, lshr, shl now have exact and nuw/nsw bits:
PR8862 / LangRef.html</li>
<li>The <a href="LangRef.html#bitwiseops">udiv, ashr, lshr, and shl</a>
instructions now have support exact and nuw/nsw bits to indicate that they
don't overflow or shift out bits. This is useful for optimization of <a
href="http://llvm.org/PR8862">pointer differences</a> and other cases.</li>
unnamed_addr + PR8927
new 'hotpatch' attribute: LangRef.html#fnattrs
<li>LLVM IR now supports the <a href="LangRef.html#globalvars">unnamed_addr</a>
attribute to indicate that constant global variables with identical
initializers can be merged. This fixed <a href="http://llvm.org/PR8927">an
issue</a> where LLVM would incorrectly merge two globals which were supposed
to have distinct addresses.</li>
<li>The new <a href="LangRef.html#fnattrs">hotpatch attribute</a> has been added
to allow runtime patching of functions.</li>
</ul>
</div>
@ -454,53 +456,61 @@ expose new optimization opportunities:</p>
release includes a few major enhancements and additions to the optimizers:</p>
<ul>
<li>LTO has been improved to use MC for parsing inline asm and now
can build large programs like Firefox 4 on both OS X and Linux.</li>
<li>Link Time Optimization (LTO) has been improved to use MC for parsing inline
assembly and now can build large programs like Firefox 4 on both Mac OS X and
Linux.</li>
<li>The new -loop-idiom pass recognizes memset/memcpy loops (and memset_pattern
on darwin), turning them into library calls, which are typically better
optimized than inline code. If you are building a libc and notice that your
memcpy and memset functions are compiled into infinite recursion, please build
with -ffreestanding or -fno-builtin to disable this pass.</li>
LoopIdiom: memset/memcpy formation and memset_pattern on darwin. Build with
-ffreestanding or -fno-builtin if your memcpy is being compiled into infinite
recursion.
TargetLibraryInfo
EarlyCSE pass.
LoopInstSimplify pass.
New <a href="WritingAnLLVMPass.html#RegionPass">RegionPass</a> infrastructure
for region-based optimizations.
Can optimize printf to iprintf when no floating point is used, for embedded
targets with smaller iprintf implementation.
<li>A new -early-cse pass does a fast pass over functions to fold constants,
simplify expressions, perform simple dead store elimination, and perform
common subexpression elimination. It does a good job at catching some of the
trivial redundancies that exist in unoptimized code, making later passes more
effective.<,/li>
Speedups to various mid-level passes:
GVN is much faster on functions with deep dominator trees / lots of BBs.
DomTree and DominatorFrontier are much faster to compute, and preserved by
more passes (so they are computed less often)
SRoA is also much faster and doesn't use DominanceFrontier.
<li>A new -loop-instsimplify pass is used to clean up loop bodies in the loop
optimizer.</li>
DSE is more aggressive with stores of different types: e.g. a large store
following a small one to the same address.
<li>The new TargetLibraryInfo interface allows mid-level optimizations to know
whether the current target's runtime library has certain functions. For
example, the optimizer can now transform integer-only printf calls to call
iprintf, allowing reduced code size for embedded C libraries (e.g. newlib).
</li>
<li>LLVM has a new <a href="WritingAnLLVMPass.html#RegionPass">RegionPass</a>
infrastructure for region-based optimizations.</li>
<li>Several optimizer passes have been substantially sped up:
GVN is much faster on functions with deep dominator trees and lots of basic
blocks. The dominator tree and dominance frontier passes are much faster to
compute, and preserved by more passes (so they are computed less often). The
-scalar-repl pass is also much faster and doesn't use DominanceFrontier.
</li>
<li>The Dead Store Elimination pass is more aggressive optimizing stores of
different types: e.g. a large store following a small one to the same address.
The MemCpyOptimizer pass handles several new forms of memcpy elimination.</li>
<li>LLVM now optimizes various idioms for overflow detection into check of the
flag register on various CPUs. For example, we now compile:
We now optimize various idioms for overflow detection into check of the flag
register on various CPUs, e.g.:
<pre>
unsigned long t = a+b;
if (t &lt; a) ...
</pre>
into:
addq %rdi, %rbx
jno LBB0_2
<pre>
addq %rdi, %rbx
jno LBB0_2
</pre>
</li>
</ul>
<!--
<p>In addition to these features that are done in 2.8, there is preliminary
support in the release for Type Based Alias Analysis
Preliminary work on TBAA but not usable in 2.8.
New CorrelatedValuePropagation pass, not on by default in 2.8 yet.
-->
</div>
<!--=========================================================================-->
@ -516,46 +526,37 @@ and a number of other related areas that CPU instruction-set level tools work
in.</p>
<ul>
<li>MC is now used by default for ELF systems on x86 and
x86-64.</li>
<li>MC supports and CodeGen uses the <tt>.loc</tt> directives for
producing line number debug info. This produces more compact line
tables.</li>
<li>MC supports the <tt>.cfi_*</tt> directives for producing DWARF
<li>ELF MC support has matured enough for the integrated assembler to be turned
on by default in Clang on X86-32 and X86-64 ELF systems.</li>
<li>MC supports and CodeGen uses the <tt>.file</tt> and <tt>.loc</tt> directives
for producing line number debug info. This produces more compact line
tables and easier to read .s files.</li>
<li>MC supports the <tt>.cfi_*</tt> directives for producing DWARF
frame information, but it is still not used by CodeGen by default.</li>
<li>COFF support?</li>
MC Assembler: X86 now generates much better diagnostics for common errors,
<li>The MC assembler now generates much better diagnostics for common errors,
is much faster at matching instructions, is much more bug-compatible with
the GAS assembler, and is now generally useful for a broad range of X86
assembly.
assembly.</li>
<li>We now have some basic <a href="CodeGenerator.html#mc">internals
documentation</a> for MC.</li>
ELF MC support: on by default in clang. There are still known missing features
for human written assembly.
<li>.td files can now specify assembler aliases directly with the <a
href="CodeGenerator.html#na_instparsing">MnemonicAlias and InstAlias</a>
tblgen classes.</li>
<li>LLVM now has an experimental format-independent object file manipulation
library (lib/Object). It supports both PE/COFF and ELF. The llvm-nm tool has
been extended to work with native object files, and the new llvm-objdump tool
supports disassembly of object files (but no relocations are displayed yet).
</li>
Some basic <a href="CodeGenerator.html#mc">internals documentation</a> for MC.
MC Assembler support for .file and .loc.
tblgen support for assembler aliases: <a
href="CodeGenerator.html#na_instparsing">MnemonicAlias and InstAlias</a>
Win32 PE-COFF support in the MC assembler has made a lot of progress in the 2.9
timeframe, but is still not generally useful. Please see
"http://llvm.org/bugs/showdependencytree.cgi?id=9100&amp;hide_resolved=1" for open bugs?
lib/Object and llvm-objdump
Experimental format independent object file manipulation library.
* Supports PE/COFF and ELF.
* llvm-nm extended to work with object files. Exactly matches
binutils-nm for the files I've tested.
* llvm-objdump added with support for disassembly (no relocations displayed).
<li>Win32 PE-COFF support in the MC assembler has made a lot of progress in the
2.9 timeframe, but is still not generally useful.</li>
</ul>
@ -707,6 +708,12 @@ from the previous release.</p>
<ul>
last release for llvm-gcc
<li>
New naming rules in coding standards: CodingStandards.html#ll_naming
</li>
- DIBuilder provides simpler interface for front ends like Clang to encode debug info in LLVM IR.
- This interface hides implementation details (e.g. DIDerivedType, existence of compile unit etc..) that any front end should not know about.
For example, DIFactory DebugFactory;