Allocations associated with pushes to EbbHeaderBlockData::predecessors account
for 4.9% of all heap allocation (calls) in CL. This change avoids almost all
of them by changing it to be a SmallVec<[PredBlock; 4]>. Dynamic instruction
count falls by 0.15%.
-Add resumable_trap, safepoint, isnull, and null instructions
-Add Stackmap struct and StackmapSink trait
Co-authored-by: Mir Ahmed <mirahmed753@gmail.com>
Co-authored-by: Dan Gohman <sunfish@mozilla.com>
