Re: [PATCH] posix: fix false regex match with backrefs and $ anchor

[Paul Eggert]

On 2026-04-13 10:40, Florian Weimer wrote:
Wouldn't it make sense to call check_halt_state_context only once?

Yes it would, and thanks. I installed the attached into Gnulib, and we 
should propagate this into glibc when we propagate the other fixes.From 8b627431703c7e7d762f9e3174336d66b558314a Mon Sep 17 00:00:00 2001
From: Paul Eggert <egg...@cs.ucla.edu>
Date: Mon, 13 Apr 2026 13:26:58 -0700
Subject: [PATCH] regex: omit unnecessary check_halt_state_context

* lib/regexec.c (prune_impossible_nodes):
Avoid unnecessary call to check_halt_state_context.
Suggested by Florian Weimer in:
https://sourceware.org/pipermail/libc-alpha/2026-April/176627.html
---
 ChangeLog     |  8 ++++++++
 lib/regexec.c | 21 ++++++++++++---------
 2 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 875e734657..98ad290692 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2026-04-13  Paul Eggert  <egg...@cs.ucla.edu>
+
+	regex: omit unnecessary check_halt_state_context
+	* lib/regexec.c (prune_impossible_nodes):
+	Avoid unnecessary call to check_halt_state_context.
+	Suggested by Florian Weimer in:
+	https://sourceware.org/pipermail/libc-alpha/2026-April/176627.html
+
 2026-04-13  Bruno Haible  <br...@clisp.org>
 
 	regex: Fix use of uninitialized variable (regression yesterday).
diff --git a/lib/regexec.c b/lib/regexec.c
index 7095c4bf5b..65d4d0f09e 100644
--- a/lib/regexec.c
+++ b/lib/regexec.c
@@ -1013,7 +1013,7 @@ prune_impossible_nodes (re_match_context_t *mctx)
 	      goto free_return;
 	  if (sifted_states[0] != NULL || lim_states[0] != NULL)
 	    break;
-	  do
+	  for (;;)
 	    {
 	      --match_last;
 	      if (match_last < 0)
@@ -1021,14 +1021,17 @@ prune_impossible_nodes (re_match_context_t *mctx)
 		  ret = REG_NOMATCH;
 		  goto free_return;
 		}
-	    } while (mctx->state_log[match_last] == NULL
-		     || !mctx->state_log[match_last]->halt
-		     || !check_halt_state_context (mctx,
-						   mctx->state_log[match_last],
-						   match_last));
-	  halt_node = check_halt_state_context (mctx,
-						mctx->state_log[match_last],
-						match_last);
+              if (mctx->state_log[match_last] != NULL
+                  && mctx->state_log[match_last]->halt)
+                {
+                  halt_node
+                    = check_halt_state_context (mctx,
+                                                mctx->state_log[match_last],
+                                                match_last);
+                  if (halt_node)
+                    break;
+                }
+	    }
 	}
       ret = merge_state_array (dfa, sifted_states, lim_states,
 			       match_last + 1);
-- 
2.53.0