An identity COPY like this:
%AL = COPY %AL, %EAX<imp-def>
has no semantic effect, but encodes liveness information: Further users
of %EAX only depend on this instruction even though it does not define
the full register.
Replace the COPY with a KILL instruction in those cases to maintain this
liveness information. (This reverts a small part of r238588 but this
time adds a comment explaining why a KILL instruction is useful).
llvm-svn: 274952
This patch uses PSHUFB to lower vector CTLZ and avoid (slower) scalarizations.
The leading zero count of each 4-bit nibble of the vector is determined by using a PSHUFB lookup. Pairs of results are then repeatedly combined up to the original element width.
Differential Revision: http://reviews.llvm.org/D20016
llvm-svn: 269646
Optimized <8 x i32> to <8 x i16>
<4 x i64> to < 4 x i32>
<16 x i16> to <16 x i8>
All these oprtrations use now AVX512F set (KNL). Before this change it was implemented with AVX2 set.
Differential Revision: http://reviews.llvm.org/D14108
llvm-svn: 251764
Matthias Braun