RPCS3/llvm-mirror
1
0
Fork 0
mirror of https://github.com/RPCS3/llvm-mirror.git synced 2024-11-24 03:33:20 +01:00
Code Issues Projects Releases Wiki Activity
Mirror of https://github.com/RPCS3/llvm-mirror
139,582 Commits 4 Branches 5 Tags 704 MiB
C++ 96.9%
C 1%
Python 1%
CMake 0.6%
OCaml 0.2%
Other 0.1%
5a58c95fb7
Go to file
James Molloy 5a58c95fb7 [Thumb-1] Synthesize TBB/TBH instructions to make use of compressed jump tables 
The TBB and TBH instructions in Thumb-2 allow jump tables to be compressed into sequences of bytes or shorts respectively. These instructions do not exist in Thumb-1, however it is possible to synthesize them out of a sequence of other instructions.

It turns out this sequence is so short that it's almost never a lose for performance and is ALWAYS a significant win for code size.

TBB example:
Before: lsls r0, r0, #2    After: add  r0, pc
        adr  r1, .LJTI0_0         ldrb r0, [r0, #6]
        ldr  r0, [r0, r1]         lsls r0, r0, #1
        mov  pc, r0               add  pc, r0
  => No change in prologue code size or dynamic instruction count. Jump table shrunk by a factor of 4.

The only case that can increase dynamic instruction count is the TBH case:

Before: lsls r0, r4, #2    After: lsls r4, r4, #1
        adr  r1, .LJTI0_0         add  r4, pc
        ldr  r0, [r0, r1]         ldrh r4, [r4, #6]
        mov  pc, r0               lsls r4, r4, #1
                                  add  pc, r4
  => 1 more instruction in prologue. Jump table shrunk by a factor of 2.

So there is an argument that this should be disabled when optimizing for performance (and a TBH needs to be generated). I'm not so sure about that in practice, because on small cores with Thumb-1 performance is often tied to code size. But I'm willing to turn it off when optimizing for performance if people want (also note that TBHs are fairly rare in practice!)

llvm-svn: 284580
2016-10-19 12:06:49 +00:00
bindings DebugInfo: change alignment type from uint64_t to uint32_t to save space. 2016-10-18 14:31:22 +00:00
cmake [docs] Increase minimum supported GCC version for building LLVM to 4.8 2016-10-18 17:17:37 +00:00
docs [docs] Increase minimum supported GCC version for building LLVM to 4.8 2016-10-18 17:17:37 +00:00
examples [Kaleidoscope] Make Chapter 2 use llvm::make_unique, rather than a helper. 2016-09-19 23:00:27 +00:00
include DenseSet: Appease msc18 to define derived constructors explicitly. 2016-10-19 05:43:17 +00:00
lib [Thumb-1] Synthesize TBB/TBH instructions to make use of compressed jump tables 2016-10-19 12:06:49 +00:00
projects [CMake] Correct configuration order of the sub-projects based on ther dependancies 2016-10-09 20:38:29 +00:00
resources In MSVC builds embed a VERSIONINFO resource in our exe and DLL files. 2015-06-12 15:58:29 +00:00
runtimes [CMake] Fixing lit for runtimes directory 2016-09-15 06:14:13 +00:00
test [Thumb-1] Synthesize TBB/TBH instructions to make use of compressed jump tables 2016-10-19 12:06:49 +00:00
tools dwarfdump: -summarize-types: print a short summary (unqualified type name, hash, length) of type units rather than dumping contents 2016-10-18 21:09:48 +00:00
unittests [asan] Simplify calculation of stack frame layout extraction calculation of stack description into separate function. 2016-10-18 23:29:52 +00:00
utils Improve tablegen gen-subtarget diagnostics for missing machine models. 2016-10-18 04:17:44 +00:00
.arcconfig project_id is from another era in phabricator land and does not provide any value. 2016-09-27 15:47:29 +00:00
.clang-format Test commit. 2014-03-02 13:08:46 +00:00
.clang-tidy .clang-tidy: correct style name is 'camelBack' not 'lowerCase'. 2016-09-13 19:04:26 +00:00
.gitignore gitignore: ignore VS Code editor files 2016-09-02 22:54:26 +00:00
CMakeLists.txt [cmake] Treat polly as "in tree" if LLVM_EXTERNAL_POLLY_SOURCE_DIR is provided 2016-10-07 21:32:47 +00:00
CODE_OWNERS.TXT Take ownership of libLTO as discussed on llvm-dev. 2016-09-15 17:42:39 +00:00
configure Remove autoconf support 2016-01-26 21:29:08 +00:00
CREDITS.TXT Shamelessly add myself to CREDITS.TXT 2016-08-04 16:28:22 +00:00
LICENSE.TXT Remove autoconf references from LICENSE.TXT 2016-08-12 20:11:03 +00:00
llvm.spec.in [Sparc] Implement i64 load/store support for 32-bit sparc. 2015-08-10 19:11:39 +00:00
LLVMBuild.txt
README.txt Revert rL277454 2016-08-02 13:26:07 +00:00
RELEASE_TESTERS.TXT Adding RELEASE_TESTERS.TXT 2016-07-21 16:46:44 +00:00

README.txt 

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

This directory and its subdirectories contain source code for LLVM,
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 are writing a package for LLVM, see docs/Packaging.rst for our
suggestions.