[RequirementMachine] Store the singleton 'Storage' instance for shape

symbols in RewriteContext.

Author: hborla

lib/AST/RequirementMachine/RewriteContext.cpp

@@ -194,7 +194,8 @@ static DebugOptions parseDebugFlags(StringRef debugFlags) {
 }
 
 RewriteContext::RewriteContext(ASTContext &ctx)
-    : Context(ctx),
+    : TheShapeSymbol(nullptr),
+      Context(ctx),
       Stats(ctx.Stats),
       SymbolHistogram(Symbol::NumKinds),
       TermHistogram(4, /*Start=*/1),

lib/AST/RequirementMachine/RewriteContext.h

@@ -45,6 +45,9 @@ class RewriteContext final {
   /// Folding set for uniquing symbols.
   llvm::FoldingSet<Symbol::Storage> Symbols;
 
+  /// The singleton storage for shape symbols.
+  Symbol::Storage *TheShapeSymbol;
+
   /// Folding set for uniquing terms.
   llvm::FoldingSet<Term::Storage> Terms;
 

lib/AST/RequirementMachine/Symbol.cpp

@@ -307,27 +307,13 @@ Symbol Symbol::forGenericParam(GenericTypeParamType *param,
 }
 
 Symbol Symbol::forShape(RewriteContext &ctx) {
-  llvm::FoldingSetNodeID id;
-  id.AddInteger(unsigned(Kind::Shape));
-
-  void *insertPos = nullptr;
-  if (auto *symbol = ctx.Symbols.FindNodeOrInsertPos(id, insertPos))
+  if (auto *symbol = ctx.TheShapeSymbol)
     return symbol;
 
   unsigned size = Storage::totalSizeToAlloc<unsigned, Term>(0, 0);
   void *mem = ctx.Allocator.Allocate(size, alignof(Storage));
   auto *symbol = new (mem) Storage(Storage::ForShape());
-
-#ifndef NDEBUG
-  llvm::FoldingSetNodeID newID;
-  symbol->Profile(newID);
-  assert(id == newID);
-#endif
-
-  ctx.Symbols.InsertNode(symbol, insertPos);
-  ctx.SymbolHistogram.add(unsigned(Kind::Shape));
-
-  return symbol;
+  return (ctx.TheShapeSymbol = symbol);
 }
 
 /// Creates a layout symbol, representing a layout constraint.