We are going to remove the old 'perfect shuffle' optimization since it
brings performance penalty in hot loop around vectors. For example, in
following loop sharing the same mask:
%v.1 = shufflevector ... <0,1,2,3,8,9,10,11,16,17,18,19,24,25,26,27>
%v.2 = shufflevector ... <0,1,2,3,8,9,10,11,16,17,18,19,24,25,26,27>
The generated instructions will be `vmrglw-vmrghw-vmrglw-vmrghw` instead
of `vperm-vperm`. In some large loop cases, this causes 20%+ performance
penalty.
The original attempt to resolve this is to pre-record masks of every
shufflevector operation in DAG, but that is somewhat complex and brings
unnecessary computation (to scan all nodes) in optimization. Here we
disable it by default. There're indeed some cases becoming worse after
this, which will be fixed in a more careful way in future patches.
Reviewed By: jsji
Differential Revision: https://reviews.llvm.org/D121082
Some of the pattern matching in PPCInstrVSX.td and node lowering involving vectors assumes 64bit mode. This patch disables some of the unsafe pattern matching and lowering of BUILD_VECTOR in 32bit mode.
Reviewed By: Xiangling_L
Differential Revision: https://reviews.llvm.org/D92789
