llvm-project/llvm
Craig Topper 784f1bbf5e [X86] Remove SRAs from v16i8 multiply lowering on sse2 targets
Previously we unpacked the even bytes of each input into the high byte of 16-bit elements then did an v8i16 arithmetic shift right by 8 bits to fill the upper bits of each word with sign bits. Then we did the v8i16 multiply and then masked to zero the upper 8-bits of each result. The similar was done for all the odd bytes. The results are then packed together with packuswb

Since we are masking each multiply result element to 8-bits, and those 8-bits are determined only by the lower 8-bits of each of the inputs, we don't need to fill the upper bits with sign bits. So we can just unpack into the low byte of each element and treat the upper bits as garbage. This is what gcc also does.

Differential Revision: https://reviews.llvm.org/D44267

llvm-svn: 327093
2018-03-09 01:22:31 +00:00
..
bindings Because of CVE-2018-6574, some compiler options and linker options are restricted to prevent arbitrary code execution. 2018-02-23 20:12:24 +00:00
cmake [cmake] Append -Wl,-rpath-link conditionally to GNULD 2018-03-08 15:09:38 +00:00
docs Use ellipsis ... to indicate omitted commands 2018-03-08 13:52:04 +00:00
examples [ORC] Consolidate RTDyldObjectLinkingLayer GetMemMgr and GetResolver into a 2018-02-14 22:13:02 +00:00
include [NFC] Factor out a helper function for checking if a block has a potential early implicit exit. 2018-03-08 21:25:30 +00:00
lib [X86] Remove SRAs from v16i8 multiply lowering on sse2 targets 2018-03-09 01:22:31 +00:00
projects
resources
runtimes
test [X86] Remove SRAs from v16i8 multiply lowering on sse2 targets 2018-03-09 01:22:31 +00:00
tools For llvm-objdump and Mach-O files, update the printing of some thread states 2018-03-08 23:10:38 +00:00
unittests [Support] Pacify -Wsign-compare in unit test. 2018-03-08 21:54:30 +00:00
utils utils: add a helper class to lit for captured substitutions 2018-03-09 00:06:10 +00:00
.arcconfig
.clang-format
.clang-tidy
.gitattributes
.gitignore
CMakeLists.txt build: add the ability to create a symlink for dsymutil 2018-02-28 23:00:50 +00:00
CODE_OWNERS.TXT
CREDITS.TXT
LICENSE.TXT
LLVMBuild.txt
README.txt
RELEASE_TESTERS.TXT
configure
llvm.spec.in

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