[llvm-cxxfilt] Added the option --no-params (#75348)

Added -p / --no-params flag to skip demangling function parameters
similar to how it is supported by GNU c++filt tool.

There are cases when users want to demangle a large number of symbols in
bulk, for example, at startup, and do not care about function parameters
and overloads at that time. Skipping the demangling of parameter types
led to a measurable improvement in performance. Our users reported about
15% speed up with GNU c++filt and we expect similar results with
llvm-cxxfilt with this patch.

1 files changed, 16 insertions, 6 deletions

diff --git a/libcxxabi/src/demangle/ItaniumDemangle.h b/libcxxabi/src/demangle/ItaniumDemangle.h
index 90f2551..5a53a18 100644
--- a/libcxxabi/src/demangle/ItaniumDemangle.h
+++ b/libcxxabi/src/demangle/ItaniumDemangle.h
@@ -2794,7 +2794,7 @@ template <typename Derived, typename Alloc> struct AbstractManglingParser {
   Node *parseClassEnumType();
   Node *parseQualifiedType();
 
-  Node *parseEncoding();
+  Node *parseEncoding(bool ParseParams = true);
   bool parseCallOffset();
   Node *parseSpecialName();
 
@@ -2911,7 +2911,7 @@ template <typename Derived, typename Alloc> struct AbstractManglingParser {
   Node *parseDestructorName();
 
   /// Top-level entry point into the parser.
-  Node *parse();
+  Node *parse(bool ParseParams = true);
 };
 
 const char* parse_discriminator(const char* first, const char* last);
@@ -5405,7 +5405,7 @@ Node *AbstractManglingParser<Derived, Alloc>::parseSpecialName() {
 //            ::= <data name>
 //            ::= <special-name>
 template <typename Derived, typename Alloc>
-Node *AbstractManglingParser<Derived, Alloc>::parseEncoding() {
+Node *AbstractManglingParser<Derived, Alloc>::parseEncoding(bool ParseParams) {
   // The template parameters of an encoding are unrelated to those of the
   // enclosing context.
   SaveTemplateParams SaveTemplateParamsScope(this);
@@ -5431,6 +5431,16 @@ Node *AbstractManglingParser<Derived, Alloc>::parseEncoding() {
   if (IsEndOfEncoding())
     return Name;
 
+  // ParseParams may be false at the top level only, when called from parse().
+  // For example in the mangled name _Z3fooILZ3BarEET_f, ParseParams may be
+  // false when demangling 3fooILZ3BarEET_f but is always true when demangling
+  // 3Bar.
+  if (!ParseParams) {
+    while (consume())
+      ;
+    return Name;
+  }
+
   Node *Attrs = nullptr;
   if (consumeIf("Ua9enable_ifI")) {
     size_t BeforeArgs = Names.size();
@@ -5895,9 +5905,9 @@ AbstractManglingParser<Derived, Alloc>::parseTemplateArgs(bool TagTemplates) {
 // extension      ::= ___Z <encoding> _block_invoke<decimal-digit>+
 // extension      ::= ___Z <encoding> _block_invoke_<decimal-digit>+
 template <typename Derived, typename Alloc>
-Node *AbstractManglingParser<Derived, Alloc>::parse() {
+Node *AbstractManglingParser<Derived, Alloc>::parse(bool ParseParams) {
   if (consumeIf("_Z") || consumeIf("__Z")) {
-    Node *Encoding = getDerived().parseEncoding();
+    Node *Encoding = getDerived().parseEncoding(ParseParams);
     if (Encoding == nullptr)
       return nullptr;
     if (look() == '.') {
@@ -5911,7 +5921,7 @@ Node *AbstractManglingParser<Derived, Alloc>::parse() {
   }
 
   if (consumeIf("___Z") || consumeIf("____Z")) {
-    Node *Encoding = getDerived().parseEncoding();
+    Node *Encoding = getDerived().parseEncoding(ParseParams);
     if (Encoding == nullptr || !consumeIf("_block_invoke"))
       return nullptr;
     bool RequireNumber = consumeIf('_');