This replaces the build_vector lowering code that was just added in
D80013
and matches the pattern later from the x86-specific "vzext_movl".
That seems to result in the same or better improvements and gets rid
of the 'TODO' items from that patch.
AFAICT, we always shrink wider constant vectors to 128-bit on these
patterns, so we still get the implicit zero-extension to ymm/zmm
without wasting space on larger vector constants. There's a trade-off
there because that means we miss potential load-folding.
Similarly, we could load scalar constants here with implicit
zero-extension even to 128-bit. That saves constant space, but it
means we forego load-folding, and so it increases register pressure.
This seems like a good middle-ground between those 2 options.
Differential Revision: https://reviews.llvm.org/D80131
Second half of PR40800, this patch adds DAG undef handling to fcmp instructions to match the behavior in llvm::ConstantFoldCompareInstruction, this permits constant folding of vector comparisons where some elements had been reduced to UNDEF (by SimplifyDemandedVectorElts etc.).
This involves a lot of tweaking to reduced tests as bugpoint loves to reduce fcmp arguments to undef........
Differential Revision: https://reviews.llvm.org/D60006
llvm-svn: 357765
