llvm-project/llvm
Chad Rosier 6db9ff64a8 [AArch64] Prefer Bcc to CBZ/CBNZ/TBZ/TBNZ when NZCV flags can be set for "free".
This patch contains a pass that transforms CBZ/CBNZ/TBZ/TBNZ instructions into a
conditional branch (Bcc), when the NZCV flags can be set for "free". This is
preferred on targets that have more flexibility when scheduling Bcc
instructions as compared to CBZ/CBNZ/TBZ/TBNZ (assuming all other variables are
equal). This can reduce register pressure and is also the default behavior for
GCC.

A few examples:

 add w8, w0, w1  -> cmn w0, w1             ; CMN is an alias of ADDS.
 cbz w8, .LBB_2  -> b.eq .LBB0_2           ; single def/use of w8 removed.

 add w8, w0, w1  -> adds w8, w0, w1        ; w8 has multiple uses.
 cbz w8, .LBB1_2 -> b.eq .LBB1_2

 sub w8, w0, w1       -> subs w8, w0, w1   ; w8 has multiple uses.
 tbz w8, #31, .LBB6_2 -> b.ge .LBB6_2

In looking at all current sub-target machine descriptions, this transformation
appears to be either positive or neutral.

Differential Revision: https://reviews.llvm.org/D34220.

llvm-svn: 306144
2017-06-23 19:20:12 +00:00
..
bindings [Go] Subtypes function 2017-06-08 07:32:29 +00:00
cmake TableGen.cmake: Use DEPFILE for Ninja Generator with CMake>=3.7. 2017-06-21 22:04:07 +00:00
docs [docs] As of binutils 2.21.51.0.2, ld.bfd supports plugins too, represent this in docs 2017-06-23 13:54:10 +00:00
examples [ORC] Switch the object layer API from addObjectSet to addObject (singular), and 2017-06-22 21:06:54 +00:00
include [llvm-pdbutil] Add a function for formatting MSF data. 2017-06-23 18:52:13 +00:00
lib [AArch64] Prefer Bcc to CBZ/CBNZ/TBZ/TBNZ when NZCV flags can be set for "free". 2017-06-23 19:20:12 +00:00
projects Add temporary workaround to allow in-tree libc++ builds on Windows 2017-05-11 01:44:30 +00:00
resources
runtimes [CMake][runtimes] Add install target for runtimes builtins 2017-06-02 19:38:11 +00:00
test [AArch64] Prefer Bcc to CBZ/CBNZ/TBZ/TBNZ when NZCV flags can be set for "free". 2017-06-23 19:20:12 +00:00
tools [llvm-pdbutil] Add a function for formatting MSF data. 2017-06-23 18:52:13 +00:00
unittests Make the size specification for cache_size_bytes case insensitive. 2017-06-23 17:13:51 +00:00
utils [TableGen] Take a parameter by reference instead of pointer so we don't have to add & on both callers. NFC 2017-06-20 16:34:37 +00:00
.arcconfig
.clang-format
.clang-tidy
.gitignore
CMakeLists.txt [Solaris] replace Solaris.h hack with a set of better hacks 2017-06-22 13:18:46 +00:00
CODE_OWNERS.TXT
CREDITS.TXT update of the url 2017-05-14 07:55:01 +00:00
LICENSE.TXT
LLVMBuild.txt
README.txt
RELEASE_TESTERS.TXT
configure
llvm.spec.in

README.txt

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