Commit Graph

3 Commits

Author SHA1 Message Date
Tamas Berghammer d12f31535a Fix MSVC 2013 build after rL260504
llvm-svn: 260511
2016-02-11 11:27:51 +00:00
Ashutosh Nema 2260a3a046 Fixed typo in comment & coding style for LoopVersioningLICM.
llvm-svn: 260504
2016-02-11 09:23:53 +00:00
Ashutosh Nema df6763abe8 New Loop Versioning LICM Pass
Summary:
When alias analysis is uncertain about the aliasing between any two accesses,
it will return MayAlias. This uncertainty from alias analysis restricts LICM
from proceeding further. In cases where alias analysis is uncertain we might
use loop versioning as an alternative.

Loop Versioning will create a version of the loop with aggressive aliasing
assumptions in addition to the original with conservative (default) aliasing
assumptions. The version of the loop making aggressive aliasing assumptions
will have all the memory accesses marked as no-alias. These two versions of
loop will be preceded by a memory runtime check. This runtime check consists
of bound checks for all unique memory accessed in loop, and it ensures the
lack of memory aliasing. The result of the runtime check determines which of
the loop versions is executed: If the runtime check detects any memory
aliasing, then the original loop is executed. Otherwise, the version with
aggressive aliasing assumptions is used.

The pass is off by default and can be enabled with command line option 
-enable-loop-versioning-licm.

Reviewers: hfinkel, anemet, chatur01, reames

Subscribers: MatzeB, grosser, joker.eph, sanjoy, javed.absar, sbaranga,
             llvm-commits

Differential Revision: http://reviews.llvm.org/D9151

llvm-svn: 259986
2016-02-06 07:47:48 +00:00