[OptTable] Precompute OptTable prefixes union table through tablegen

This avoid rediscovering this table when reading each options, providing
a sensible 2% speedup when processing and empty file, and a measurable
speedup on typical workloads, see:

This is optional, the legacy, on-the-fly, approach can still be used
through the GenericOptTable class, while the new one is used through
PrecomputedOptTable.

https://llvm-compile-time-tracker.com/compare.php?from=4da6cb3202817ee2897d6b690e4af950459caea4&to=19a492b704e8f5c1dea120b9c0d3859bd78796be&stat=instructions:u

Differential Revision: https://reviews.llvm.org/D140800

1 files changed, 4 insertions, 2 deletions

diff --git a/llvm/tools/llvm-ifs/llvm-ifs.cpp b/llvm/tools/llvm-ifs/llvm-ifs.cpp
index 0c85a1f..0ca9dfd 100644
--- a/llvm/tools/llvm-ifs/llvm-ifs.cpp
+++ b/llvm/tools/llvm-ifs/llvm-ifs.cpp
@@ -79,9 +79,11 @@ static constexpr opt::OptTable::Info InfoTable[] = {
 #undef OPTION
 };
 
-class IFSOptTable : public opt::OptTable {
+class IFSOptTable : public opt::GenericOptTable {
 public:
-  IFSOptTable() : OptTable(InfoTable) { setGroupedShortOptions(true); }
+  IFSOptTable() : opt::GenericOptTable(InfoTable) {
+    setGroupedShortOptions(true);
+  }
 };
 
 struct DriverConfig {