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Kostya Kortchinsky b0e96eb28e [scudo] CRC32 optimizations 
Summary:
This change optimizes several aspects of the checksum used for chunk headers.

First, there is no point in checking the weak symbol `computeHardwareCRC32`
everytime, it will either be there or not when we start, so check it once
during initialization and set the checksum type accordingly.

Then, the loading of `HashAlgorithm` for SSE versions (and ARM equivalent) was
not optimized out, while not necessary. So I reshuffled that part of the code,
which duplicates a tiny bit of code, but ends up in a much cleaner assembly
(and faster as we avoid an extraneous load and some calls).

The following code is the checksum at the end of `scudoMalloc` for x86_64 with
full SSE 4.2, before:
```
mov     rax, 0FFFFFFFFFFFFFFh
shl     r10, 38h
mov     edi, dword ptr cs:_ZN7__scudoL6CookieE ; __scudo::Cookie
and     r14, rax
lea     rsi, [r13-10h]
movzx   eax, cs:_ZN7__scudoL13HashAlgorithmE ; __scudo::HashAlgorithm
or      r14, r10
mov     rbx, r14
xor     bx, bx
call    _ZN7__scudo20computeHardwareCRC32Ejm ; __scudo::computeHardwareCRC32(uint,ulong)
mov     rsi, rbx
mov     edi, eax
call    _ZN7__scudo20computeHardwareCRC32Ejm ; __scudo::computeHardwareCRC32(uint,ulong)
mov     r14w, ax
mov     rax, r13
mov     [r13-10h], r14
```
After:
```
mov     rax, cs:_ZN7__scudoL6CookieE ; __scudo::Cookie
lea     rcx, [rbx-10h]
mov     rdx, 0FFFFFFFFFFFFFFh
and     r14, rdx
shl     r9, 38h
or      r14, r9
crc32   eax, rcx
mov     rdx, r14
xor     dx, dx
mov     eax, eax
crc32   eax, rdx
mov     r14w, ax
mov     rax, rbx
mov     [rbx-10h], r14
```

Reviewers: dvyukov, alekseyshl, kcc

Reviewed By: alekseyshl

Subscribers: aemerson, rengolin, llvm-commits

Differential Revision: https://reviews.llvm.org/D32971

llvm-svn: 302538
 		2017-05-09 15:12:38 +00:00
..
cmake Roll back r301831 to fix broken powerpc64le tests. 2017-05-02 16:43:39 +00:00
docs [sanitizers] Make it possible to XFAIL on the effective target, not just the default. 2016-08-09 11:50:53 +00:00
include [XRay][compiler-rt] Add function id utilities for XRay 2017-05-05 01:27:11 +00:00
lib [scudo] CRC32 optimizations 2017-05-09 15:12:38 +00:00
test [powerpc] Remove XFAIL for sanitizer_coverage_no_prune.cc on powerpc64 2017-05-08 15:17:43 +00:00
unittests Add missing import 2017-04-07 01:24:48 +00:00
www Update references to new lists.llvm.org mailing lists. 2015-08-05 03:58:00 +00:00
.arcconfig Upgrade all the .arcconfigs to https. 2016-07-14 13:15:37 +00:00
.gitignore
…
CMakeLists.txt [sanitizers] Avoid using -fomit-frame-pointer on Darwin 2017-03-27 17:14:48 +00:00
CODE_OWNERS.TXT [sanitizers] remove earthdok@ from owners 2016-05-18 18:52:18 +00:00
CREDITS.TXT
…
LICENSE.TXT Update copyright year to 2016. 2016-03-30 22:38:50 +00:00
README.txt
…

README.txt 

Compiler-RT
================================

This directory and its subdirectories contain source code for the compiler
support routines.

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

================================