Ayal Zaks e1f7499ee7 [LV] Test once if vector trip count is zero, instead of twice ...

Generate a single test to decide if there are enough iterations to jump to the
vectorized loop, or else go to the scalar remainder loop. This test compares the
Scalar Trip Count: if STC < VF * UF go to the scalar loop. If
requiresScalarEpilogue() holds, at-least one iteration must remain scalar; the
rest can be used to form vector iterations. So in this case the test checks
instead if (STC - 1) < VF * UF by comparing STC <= VF * UF, and going to the
scalar loop if so. Otherwise the vector loop is entered for at-least one vector
iteration.

This test covers the case where incrementing the backedge-taken count will
overflow leading to an incorrect trip count of zero. In this (rare) case we will
also avoid the vector loop and jump to the scalar loop.

This patch simplifies the existing tests and effectively removes the basic-block
originally named "min.iters.checked", leaving the single test in block
"vector.ph".

Original observation and initial patch by Evgeny Stupachenko.

Differential Revision: https://reviews.llvm.org/D34150


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@308421 91177308-0d34-0410-b5e6-96231b3b80d8

2017-07-19 05:16:39 +00:00

..

CMakeLists.txt

Remove the BBVectorize pass.

2017-06-30 07:09:08 +00:00

LLVMBuild.txt

Update libdeps since TLI was moved from Target to Analysis in r226078.

2015-01-15 05:21:00 +00:00

LoadStoreVectorizer.cpp

[KnownBits] Add bit counting methods to KnownBits struct and use them where possible

2017-05-12 17:20:30 +00:00

LoopVectorize.cpp

[LV] Test once if vector trip count is zero, instead of twice

2017-07-19 05:16:39 +00:00

SLPVectorizer.cpp

Remove unnecessary cast. NFCI.

2017-07-17 09:35:03 +00:00

Vectorize.cpp

Remove the BBVectorize pass.

2017-06-30 07:09:08 +00:00