Reapply r249121 : "[FastISel][x86] Teach how to select SSE2/AVX bitcasts between 128/256-bit vector types."
This patch teaches FastIsel the following two things:
1) On SSE2, no instructions are needed for bitcasts between 128-bit vector types;
2) On AVX, no instructions are needed for bitcasts between 256-bit vector types.
Example:
%1 = bitcast <4 x i31> %V to <2 x i64>
Before (-fast-isel -fast-isel-abort=1):
FastIsel miss: %1 = bitcast <4 x i31> %V to <2 x i64>
Now we don't fall back to SelectionDAG and we correctly fold that computation
propagating the register associated to %V.
Originally reviewed here: http://reviews.llvm.org/D13347
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@249147
91177308-0d34-0410-b5e6-
96231b3b80d8