[Profiler] Simplify CounterExpr

This class is more or less just duplicating LLVM's
`Counter` class, as such we can just wrap it
directly and avoid having to construct it later.
This also avoids building up unnecessarily large
counter expressions and doing quadratic amounts of
counter simplification work that we were previously
doing.

rdar://118185163

Author: hamishknight

include/swift/SIL/SILCoverageMap.h

@@ -127,7 +127,16 @@ class SILCoverageMap : public llvm::ilist_node<SILCoverageMap>,
     return Expressions;
   }
 
-  void printCounter(llvm::raw_ostream &OS, llvm::coverage::Counter C) const;
+  /// Print a given profiling counter expression, given the reference to the
+  /// counter, and the list of counters it may reference.
+  static void
+  printCounter(llvm::raw_ostream &OS, llvm::coverage::Counter C,
+               ArrayRef<llvm::coverage::CounterExpression> Expressions);
+
+  /// Print a given profiling counter expression.
+  void printCounter(llvm::raw_ostream &OS, llvm::coverage::Counter C) const {
+    printCounter(OS, C, getExpressions());
+  }
 
   /// Print the coverage map.
   void print(llvm::raw_ostream &OS, bool Verbose = false,

lib/SIL/IR/SILCoverageMap.cpp

@@ -86,7 +86,8 @@ struct Printer {
 };
 } // end anonymous namespace
 
-void SILCoverageMap::printCounter(llvm::raw_ostream &OS,
-                                  llvm::coverage::Counter C) const {
-  OS << Printer(C, getExpressions());
+void SILCoverageMap::printCounter(
+    llvm::raw_ostream &OS, llvm::coverage::Counter C,
+    ArrayRef<llvm::coverage::CounterExpression> Expressions) {
+  OS << Printer(C, Expressions);
 }