From b78e77b34c14b0f127b22e252309527e84967dcc Mon Sep 17 00:00:00 2001
From: pennae <github@quasiparticle.net>
Date: Sun, 10 Dec 2023 13:00:18 +0100
Subject: [PATCH] use custom location type in the parser
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~1% parser speedup from not using TLS indirections, less on system eval.
this could have also gone in flex yyextra data, but that's significantly
slower for some reason (albeit still faster than thread locals).

before:

  Time (mean ± σ):      4.231 s ±  0.004 s    [User: 3.725 s, System: 0.504 s]
  Range (min … max):    4.226 s …  4.240 s    10 runs

after:

  Time (mean ± σ):      4.224 s ±  0.005 s    [User: 3.711 s, System: 0.512 s]
  Range (min … max):    4.218 s …  4.234 s    10 runs
---
 src/libexpr/lexer.l  |  9 +++------
 src/libexpr/parser.y | 25 +++++++++++++++++++++++++
 2 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/src/libexpr/lexer.l b/src/libexpr/lexer.l
index 9a35dd594..df2cbd06f 100644
--- a/src/libexpr/lexer.l
+++ b/src/libexpr/lexer.l
@@ -36,9 +36,6 @@ static inline PosIdx makeCurPos(const YYLTYPE & loc, ParseData * data)
 
 #define CUR_POS makeCurPos(*yylloc, data)
 
-// backup to recover from yyless(0)
-thread_local YYLTYPE prev_yylloc;
-
 static void initLoc(YYLTYPE * loc)
 {
     loc->first_line = loc->last_line = 1;
@@ -47,7 +44,7 @@ static void initLoc(YYLTYPE * loc)
 
 static void adjustLoc(YYLTYPE * loc, const char * s, size_t len)
 {
-    prev_yylloc = *loc;
+    loc->stash();
 
     loc->first_line = loc->last_line;
     loc->first_column = loc->last_column;
@@ -231,7 +228,7 @@ or          { return OR_KW; }
 {HPATH_START}\$\{ {
   PUSH_STATE(PATH_START);
   yyless(0);
-  *yylloc = prev_yylloc;
+  yylloc->unstash();
 }
 
 <PATH_START>{PATH_SEG} {
@@ -287,7 +284,7 @@ or          { return OR_KW; }
      context (it may be ')', ';', or something of that sort) */
   POP_STATE();
   yyless(0);
-  *yylloc = prev_yylloc;
+  yylloc->unstash();
   return PATH_END;
 }
 
diff --git a/src/libexpr/parser.y b/src/libexpr/parser.y
index 16ad8af2e..b331776f0 100644
--- a/src/libexpr/parser.y
+++ b/src/libexpr/parser.y
@@ -28,6 +28,31 @@
 
 namespace nix {
 
+#define YYLTYPE ::nix::ParserLocation
+    struct ParserLocation
+    {
+        int first_line, first_column;
+        int last_line, last_column;
+
+        // backup to recover from yyless(0)
+        int stashed_first_line, stashed_first_column;
+        int stashed_last_line, stashed_last_column;
+
+        void stash() {
+          stashed_first_line = first_line;
+          stashed_first_column = first_column;
+          stashed_last_line = last_line;
+          stashed_last_column = last_column;
+        }
+
+        void unstash() {
+          first_line = stashed_first_line;
+          first_column = stashed_first_column;
+          last_line = stashed_last_line;
+          last_column = stashed_last_column;
+        }
+    };
+
     struct ParseData
     {
         EvalState & state;