[MC] Eliminate two symbol-related hash maps (#95464)

Previously, a symbol insertion requires (at least) three hash table
operations:

- Lookup/create entry in Symbols (main symbol table)
- Lookup NextUniqueID to deduplicate identical temporary labels
- Add entry to UsedNames, which is also used to serve as storage for the
symbol name in the MCSymbol.

All three lookups are done with the same name, so combining these into a
single table reduces the number of lookups to one. Thus, a pointer to a
symbol table entry can be passed to createSymbol to avoid a duplicate
lookup of the same name.

The new symbol table entry value is placed in a separate header to avoid
including MCContext in MCSymbol or vice versa.

1 files changed, 2 insertions, 2 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
index 0b7ec6e..b0a97c7 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
@@ -319,8 +319,8 @@ void WebAssemblyAsmPrinter::emitDecls(const Module &M) {
     // Emit .globaltype, .tagtype, or .tabletype declarations for extern
     // declarations, i.e. those that have only been declared (but not defined)
     // in the current module
-    auto Sym = cast<MCSymbolWasm>(It.getValue());
-    if (!Sym->isDefined())
+    auto Sym = cast_or_null<MCSymbolWasm>(It.getValue().Symbol);
+    if (Sym && !Sym->isDefined())
       emitSymbolType(Sym);
   }