[RegAllocFast] Use uint16_t SparseT for LiveRegMap

For functions with very large numbers of live variables, lookups into
LiveRegMap previously detoriated to linear searches.

This slightly increases memory usage, but that is barely measurable.

Reviewed By: arsenm

Differential Revision: https://reviews.llvm.org/D149330

diff --git a/llvm/lib/CodeGen/RegAllocFast.cpp b/llvm/lib/CodeGen/RegAllocFast.cpp
index f60e176..17df5d6 100644 (file)
--- a/llvm/lib/CodeGen/RegAllocFast.cpp
+++ b/llvm/lib/CodeGen/RegAllocFast.cpp
@@ -106,7 +106,7 @@ namespace {
       }
     };
 
-    using LiveRegMap = SparseSet<LiveReg>;
+    using LiveRegMap = SparseSet<LiveReg, identity<unsigned>, uint16_t>;
     /// This map contains entries for each virtual register that is currently
     /// available in a physical register.
     LiveRegMap LiveVirtRegs;