[PowerPC] Adjust load/store costs in PPCTTI

This provides more realistic costs for the insert/extractelement instructions
(which are load/store pairs), accounts for the cheap unaligned Altivec load
sequence, and for unaligned VSX load/stores.

Bad news:
MultiSource/Applications/sgefa/sgefa - 35% slowdown (this will require more investigation)
SingleSource/Benchmarks/McGill/queens - 20% slowdown (we no longer vectorize this, but it was a constant store that was scalarized)
MultiSource/Benchmarks/FreeBench/pcompress2/pcompress2 - 2% slowdown

Good news:
SingleSource/Benchmarks/Shootout/ary3 - 54% speedup
SingleSource/Benchmarks/Shootout-C++/ary - 40% speedup
MultiSource/Benchmarks/Ptrdist/ks/ks - 35% speedup
MultiSource/Benchmarks/FreeBench/neural/neural - 30% speedup
MultiSource/Benchmarks/TSVC/Symbolics-flt/Symbolics-flt - 20% speedup

Unfortunately, estimating the costs of the stack-based scalarization sequences
is hard, and adjusting these costs is like a game of whac-a-mole :( I'll
revisit this again after we have better codegen for vector extloads and
truncstores and unaligned load/stores.

llvm-svn: 205658
diff --git a/llvm/test/Analysis/CostModel/PowerPC/ext.ll b/llvm/test/Analysis/CostModel/PowerPC/ext.ll
index daaa8f5..7d6a14e 100644
--- a/llvm/test/Analysis/CostModel/PowerPC/ext.ll
+++ b/llvm/test/Analysis/CostModel/PowerPC/ext.ll
@@ -13,7 +13,7 @@
   ; CHECK: cost of 1 {{.*}} sext
   %v3 = sext <4 x i16> undef to <4 x i32>
 
-  ; CHECK: cost of 216 {{.*}} sext
+  ; CHECK: cost of 112 {{.*}} sext
   %v4 = sext <8 x i16> undef to <8 x i32>
 
   ret void