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Arnold Schwaighofer f7af1987dd SimplifyCFG: If convert single conditional stores 
This transformation will transform a conditional store with a preceeding
uncondtional store to the same location:

 a[i] =
 may-alias with a[i] load
 if (cond)
   a[i] = Y

into an unconditional store.

 a[i] = X
 may-alias with a[i] load
 tmp = cond ? Y : X;
 a[i] = tmp

We assume that on average the cost of a mispredicted branch is going to be
higher than the cost of a second store to the same location, and that the
secondary benefits of creating a bigger basic block for other optimizations to
work on outway the potential case were the branch would be correctly predicted
and the cost of the executing the second store would be noticably reflected in
performance.

hmmer's execution time improves by 30% on an imac12,2 on ref data sets. With
this change we are on par with gcc's performance (gcc also performs this
transformation). There was a 1.2 % performance improvement on a ARM swift chip.
Other tests in the test-suite+external seem to be mostly uninfluenced in my
experiments:
This optimization was triggered on 41 tests such that the executable was
different before/after the patch. Only 1 out of the 40 tests (dealII) was
reproducable below 100% (by about .4%). Given that hmmer benefits so much I
believe this to be a fair trade off.

I am going to watch performance numbers across the builtbots and will revert
this if anything unexpected comes up.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179957 91177308-0d34-0410-b5e6-96231b3b80d8
2013-04-20 21:42:09 +00:00
autoconf Refine fenv.h handling: check if the desired macros exist, before using 2013-03-25 13:13:33 +00:00
bindings [python] Add markup option to disassembler 2012-12-01 21:57:30 +00:00
cmake Don't explicitly provide -pie in MSan bootstrap of LLVM, as it's now implied by the driver 2013-04-12 07:18:55 +00:00
docs Add CodeGen support for functions that always return arguments via a new parameter attribute 'returned', which is taken advantage of in target-independent tail call opportunity detection and in ARM call lowering (when placed on an integral first parameter). 2013-04-20 05:14:40 +00:00
examples Update links to "Itanium C++ ABI: Exception Handling" document 2013-01-13 15:53:09 +00:00
include Remove unused ShouldFoldAtomicFences flag. 2013-04-20 12:32:43 +00:00
lib SimplifyCFG: If convert single conditional stores 2013-04-20 21:42:09 +00:00
projects Print a warning message if compiler-rt can't be built because of old CMake version to make this requirement more visible to users 2013-03-05 14:43:07 +00:00
runtime Remove GCDAProfiling.c. This copy is old, the copy in compiler-rt is newer and 2013-03-07 02:03:08 +00:00
test SimplifyCFG: If convert single conditional stores 2013-04-20 21:42:09 +00:00
tools Remove dead code. 2013-04-20 11:06:34 +00:00
unittests Create a stub for DWARF parser unittests 2013-04-17 08:29:02 +00:00
utils [asm parser] Add support for predicating MnemonicAlias based on the assembler 2013-04-18 22:35:36 +00:00
.arcconfig Add .arcconfig to the repository. Useful if someone wants to use phabricator's command line tool. 2012-12-01 12:07:58 +00:00
.gitignore Add extra vim swap file pattern 2012-10-09 23:48:34 +00:00
CMakeLists.txt Enable all targets by default on Visual Studio. 2013-04-15 11:53:05 +00:00
CODE_OWNERS.TXT Fix random typo. 2013-04-17 03:18:49 +00:00
configure Refine fenv.h handling: check if the desired macros exist, before using 2013-03-25 13:13:33 +00:00
CREDITS.TXT Add myself in the CREDITS.TXT 2013-04-11 13:15:39 +00:00
LICENSE.TXT Add LICENSE.TXT covering contributions made by ARM. 2013-01-07 10:04:49 +00:00
llvm.spec.in Tidy up. s/Low Level Virtual Machine/LLVM/. 2012-01-25 22:00:23 +00:00
LLVMBuild.txt LLVMBuild: Introduce a common section which currently has a list of the 2011-12-12 22:45:54 +00:00
Makefile Improved svn repo searching for 'make update' 2013-01-28 03:19:57 +00:00
Makefile.common Makefile.common: Update a description, s/Source/SOURCES/ , according to MakefileGuide.html#control-variables . 2012-12-07 01:43:23 +00:00
Makefile.config.in Turn anonymous type in anonymous union warning back on after cleaning up 2013-03-15 00:43:00 +00:00
Makefile.rules Make check depend on all. 2013-04-09 19:42:12 +00:00
README.txt test 2013-04-17 05:34:03 +00:00

README.txt 

Low Level Virtual Machine (LLVM)
================================

This directory and its subdirectories contain source code for the Low Level
Virtual Machine, a toolkit for the construction of highly optimized compilers,
optimizers, and runtime environments.

LLVM is open source software. You may freely distribute it under the terms of
the license agreement found in LICENSE.txt.

Please see the documentation provided in docs/ for further
assistance with LLVM, and in particular docs/GettingStarted.rst for getting
started with LLVM and docs/README.txt for an overview of LLVM's
documentation setup.

If you're writing a package for LLVM, see docs/Packaging.rst for our
suggestions.