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| author | Pierre Gousseau <pierregousseau14@gmail.com> | 2016-10-14 16:41:38 +0000 |
|---|---|---|
| committer | Pierre Gousseau <pierregousseau14@gmail.com> | 2016-10-14 16:41:38 +0000 |
| commit | b6d652adb5b12b7d1fc7e973a5afc019875cb547 (patch) | |
| tree | a8196cccb70b3ebb8eba63d17f04efa2f7f31fde /llvm/lib/CodeGen/SafeStack.cpp | |
| parent | 6d6eca5cdc995fdb8850fd5c79d1018893a44988 (diff) | |
| download | llvm-b6d652adb5b12b7d1fc7e973a5afc019875cb547.zip llvm-b6d652adb5b12b7d1fc7e973a5afc019875cb547.tar.gz llvm-b6d652adb5b12b7d1fc7e973a5afc019875cb547.tar.bz2 | |
[X86] Take advantage of the lzcnt instruction on btver2 architectures when ORing comparisons to zero.
This change adds transformations such as:
zext(or(setcc(eq, (cmp x, 0)), setcc(eq, (cmp y, 0))))
To:
srl(or(ctlz(x), ctlz(y)), log2(bitsize(x))
This optimisation is beneficial on Jaguar architecture only, where lzcnt has a good reciprocal throughput.
Other architectures such as Intel's Haswell/Broadwell or AMD's Bulldozer/PileDriver do not benefit from it.
For this reason the change also adds a "HasFastLZCNT" feature which gets enabled for Jaguar.
Differential Revision: https://reviews.llvm.org/D23446
llvm-svn: 284248
Diffstat (limited to 'llvm/lib/CodeGen/SafeStack.cpp')
0 files changed, 0 insertions, 0 deletions