[RISCV] Speed up RISCVISAInfo::updateImplication.

We don't need to use a SmallSetVector to keep track of the worklist.
We only insert into the worklist if the extension is not already
in the Exts map. We immediately add it the Exts map at the same
time we add it to the worklist. If we encounter the extension again
it will already be in Exts so we won't try to add it to the worklist
again. We can just use a SmallVector for the Worklist.

Author: topperc

llvm/lib/TargetParser/RISCVISAInfo.cpp

@@ -840,9 +840,9 @@ void RISCVISAInfo::updateImplication() {
 
   // This loop may execute over 1 iteration since implication can be layered
   // Exits loop if no more implication is applied
-  SmallSetVector<StringRef, 16> WorkList;
+  SmallVector<StringRef, 16> WorkList;
   for (auto const &Ext : Exts)
-    WorkList.insert(Ext.first);
+    WorkList.push_back(Ext.first);
 
   while (!WorkList.empty()) {
     StringRef ExtName = WorkList.pop_back_val();
@@ -851,13 +851,11 @@ void RISCVISAInfo::updateImplication() {
     std::for_each(Range.first, Range.second,
                   [&](const ImpliedExtsEntry &Implied) {
                     const char *ImpliedExt = Implied.ImpliedExt;
-                    if (WorkList.count(ImpliedExt))
-                      return;
                     if (Exts.count(ImpliedExt))
                       return;
                     auto Version = findDefaultVersion(ImpliedExt);
                     addExtension(ImpliedExt, *Version);
-                    WorkList.insert(ImpliedExt);
+                    WorkList.push_back(ImpliedExt);
                   });
   }