[PATCH] D130747: [pseudo] wip/prototype: eliminate identifier ambiguities in the grammar.

[Haojian Wu via Phabricator via cfe-commits]

hokein updated this revision to Diff 453098.
hokein added a comment.

update based on the offline discussion -- we'd like to keep all categories of
IDENTIFIER (type-name, namespace-name, template-name, template-name) as they
are useful in disambiguation, but we eliminate the ambiguities per each category

- eliminate all different type rules (class-name, enum-name, typedef-name), fold them into a unified type-name, this removes the #1 type-name ambiguity, and gives us a big performance boost;
- remove the namespace-alis rules, as they're less interesting and marginal useful;


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D130747/new/

https://reviews.llvm.org/D130747

Files:
  clang-tools-extra/pseudo/lib/cxx/cxx.bnf
  clang-tools-extra/pseudo/test/glr.cpp


Index: clang-tools-extra/pseudo/test/glr.cpp
===================================================================
--- clang-tools-extra/pseudo/test/glr.cpp
+++ clang-tools-extra/pseudo/test/glr.cpp
@@ -12,10 +12,7 @@
 // CHECK-NEXT: │ └─; := tok[8]
 // CHECK-NEXT: └─statement~simple-declaration := decl-specifier-seq init-declarator-list ;
 // CHECK-NEXT:   ├─decl-specifier-seq~simple-type-specifier := <ambiguous>
-// CHECK-NEXT:   │ ├─simple-type-specifier~type-name := <ambiguous>
-// CHECK-NEXT:   │ │ ├─type-name~IDENTIFIER := tok[5]
-// CHECK-NEXT:   │ │ ├─type-name~IDENTIFIER := tok[5]
-// CHECK-NEXT:   │ │ └─type-name~IDENTIFIER := tok[5]
+// CHECK-NEXT:   │ ├─simple-type-specifier~IDENTIFIER := tok[5]
 // CHECK-NEXT:   │ └─simple-type-specifier~IDENTIFIER := tok[5]
 // CHECK-NEXT:   ├─init-declarator-list~ptr-declarator := ptr-operator ptr-declarator
 // CHECK-NEXT:   │ ├─ptr-operator~* := tok[6]
@@ -23,12 +20,11 @@
 // CHECK-NEXT:   └─; := tok[8]
 }
 
-// CHECK:      3 Ambiguous nodes:
+// CHECK:      2 Ambiguous nodes:
 // CHECK-NEXT: 1 simple-type-specifier
 // CHECK-NEXT: 1 statement
-// CHECK-NEXT: 1 type-name
 // CHECK-EMPTY:
 // CHECK-NEXT: 0 Opaque nodes:
 // CHECK-EMPTY:
-// CHECK-NEXT: Ambiguity: 0.40 misparses/token
+// CHECK-NEXT: Ambiguity: 0.20 misparses/token
 // CHECK-NEXT: Unparsed: 0.00%
Index: clang-tools-extra/pseudo/lib/cxx/cxx.bnf
===================================================================
--- clang-tools-extra/pseudo/lib/cxx/cxx.bnf
+++ clang-tools-extra/pseudo/lib/cxx/cxx.bnf
@@ -34,14 +34,10 @@
 _ := declaration-seq
 
 # gram.key
-typedef-name := IDENTIFIER
-typedef-name := simple-template-id
+#! No namespace-alis rules, as they're less interesting and marginal useful.
 namespace-name := IDENTIFIER
-namespace-name := namespace-alias
-namespace-alias := IDENTIFIER
 class-name := IDENTIFIER
 class-name := simple-template-id
-enum-name := IDENTIFIER
 template-name := IDENTIFIER
 
 # gram.basic
@@ -391,9 +387,12 @@
 builtin-type := FLOAT
 builtin-type := DOUBLE
 builtin-type := VOID
-type-name := class-name
-type-name := enum-name
-type-name := typedef-name
+#! Unlike C++ standard grammar, we don't distinguish the underlying type (class,
+#! enum, typedef) of the IDENTIFIER, as these ambiguities are "local" and don't
+#! affect the final parse tree. Eliminating them gives a significant performance
+#! boost to the parser.
+type-name := IDENTIFIER
+type-name := simple-template-id
 elaborated-type-specifier := class-key nested-name-specifier_opt IDENTIFIER
 elaborated-type-specifier := class-key simple-template-id
 elaborated-type-specifier := class-key nested-name-specifier TEMPLATE_opt simple-template-id


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