[Demangle][Rust] Parse dot suffix

Allow mangled names to include an arbitrary dot suffix, akin to vendor
specific suffix in Itanium mangling.

Primary motivation is a support for symbols renamed during ThinLTO
import / promotion (ThinLTO is the default configuration for optimized
builds in rustc).

Reviewed By: dblaikie

Differential Revision: https://reviews.llvm.org/D104358

llvm/lib/Demangle/RustDemangle.cpp

@@ -109,7 +109,9 @@ bool Demangler::demangle(StringView Mangled) {
     Error = true;
     return false;
   }
-  Input = Mangled;
+  size_t Dot = Mangled.find('.');
+  Input = Mangled.substr(0, Dot);
+  StringView Suffix = Mangled.dropFront(Dot);
 
   demanglePath(rust_demangle::InType::No);
 
@@ -121,6 +123,12 @@ bool Demangler::demangle(StringView Mangled) {
   if (Position != Input.size())
     Error = true;
 
+  if (!Suffix.empty()) {
+    print(" (");
+    print(Suffix);
+    print(")");
+  }
+
   return !Error;
 }
 

llvm/test/Demangle/rust.test

@@ -448,6 +448,14 @@ CHECK: _RIC7backrefSB9_E
 CHECK: _RIC7backrefKBa_E
        _RIC7backrefKBa_E
 
+; Dot suffix
+
+CHECK: dot (.llvm.1234)
+       _RC3dot.llvm.1234
+
+CHECK: dot (.llvm.6789)
+       _RC3dotC5crate.llvm.6789
+
 ; Invalid mangled characters
 
 CHECK: _RNvC2a.1c