From eb77572257bfa4e649c0c8852d2d0a58ad63eaa5 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Mon, 24 Aug 2020 13:12:51 -0700
Subject: [PATCH] Fix replace-region-contents performance bug

Backport from master.
* src/editfns.c (rbc_quitcounter): Remove; the quitcounter
is now part of the context.
(EXTRA_CONTEXT_FIELDS): Remove unused member early_abort_tests.
Add jmp, quitcounter.
(Freplace_buffer_contents): Use setjmp/longjmp to recover from
a compareseq that runs too long.  Omit unnecessary rarely_quit
call.
(buffer_chars_equal): Occasionally check for early abort and
longjmp out if so (Bug#43016).
---
 src/editfns.c | 31 +++++++++++++++----------------
 1 file changed, 15 insertions(+), 16 deletions(-)

diff --git a/src/editfns.c b/src/editfns.c
index fe1feaf1e77..f660513b2a4 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -1913,9 +1913,6 @@ determines whether case is significant or ignored.  */)
 #undef EQUAL
 #define USE_HEURISTIC
 
-/* Counter used to rarely_quit in replace-buffer-contents.  */
-static unsigned short rbc_quitcounter;
-
 #define XVECREF_YVECREF_EQUAL(ctx, xoff, yoff)  \
   buffer_chars_equal ((ctx), (xoff), (yoff))
 
@@ -1936,7 +1933,8 @@ static unsigned short rbc_quitcounter;
   unsigned char *deletions;                     \
   unsigned char *insertions;			\
   struct timespec time_limit;			\
-  unsigned int early_abort_tests;
+  sys_jmp_buf jmp;				\
+  unsigned short quitcounter;
 
 #define NOTE_DELETE(ctx, xoff) set_bit ((ctx)->deletions, (xoff))
 #define NOTE_INSERT(ctx, yoff) set_bit ((ctx)->insertions, (yoff))
@@ -2065,14 +2063,17 @@ nil.  */)
     .heuristic = true,
     .too_expensive = XFIXNUM (max_costs),
     .time_limit = time_limit,
-    .early_abort_tests = 0
   };
   memclear (ctx.deletions, del_bytes);
   memclear (ctx.insertions, ins_bytes);
 
   /* compareseq requires indices to be zero-based.  We add BEGV back
      later.  */
-  bool early_abort = compareseq (0, size_a, 0, size_b, false, &ctx);
+  bool early_abort;
+  if (! sys_setjmp (ctx.jmp))
+    early_abort = compareseq (0, size_a, 0, size_b, false, &ctx);
+  else
+    early_abort = true;
 
   if (early_abort)
     {
@@ -2082,8 +2083,6 @@ nil.  */)
       return Qnil;
     }
 
-  rbc_quitcounter = 0;
-
   Fundo_boundary ();
   bool modification_hooks_inhibited = false;
   record_unwind_protect_excursion ();
@@ -2107,8 +2106,7 @@ nil.  */)
      walk backwards, we don’t have to keep the positions in sync.  */
   while (i >= 0 || j >= 0)
     {
-      /* Allow the user to quit if this gets too slow.  */
-      rarely_quit (++rbc_quitcounter);
+      rarely_quit (++ctx.quitcounter);
 
       /* Check whether there is a change (insertion or deletion)
          before the current position.  */
@@ -2123,8 +2121,6 @@ nil.  */)
 	  while (j > 0 && bit_is_set (ctx.insertions, j - 1))
             --j;
 
-	  rarely_quit (rbc_quitcounter++);
-
           ptrdiff_t beg_a = min_a + i;
           ptrdiff_t beg_b = min_b + j;
           eassert (beg_a <= end_a);
@@ -2144,7 +2140,6 @@ nil.  */)
     }
 
   SAFE_FREE_UNBIND_TO (count, Qnil);
-  rbc_quitcounter = 0;
 
   if (modification_hooks_inhibited)
     {
@@ -2191,12 +2186,16 @@ static bool
 buffer_chars_equal (struct context *ctx,
                     ptrdiff_t pos_a, ptrdiff_t pos_b)
 {
+  if (!++ctx->quitcounter)
+    {
+      maybe_quit ();
+      if (compareseq_early_abort (ctx))
+	sys_longjmp (ctx->jmp, 1);
+    }
+
   pos_a += ctx->beg_a;
   pos_b += ctx->beg_b;
 
-  /* Allow the user to escape out of a slow compareseq call.  */
-  rarely_quit (++rbc_quitcounter);
-
   ptrdiff_t bpos_a =
     ctx->a_unibyte ? pos_a : buf_charpos_to_bytepos (ctx->buffer_a, pos_a);
   ptrdiff_t bpos_b =
-- 
2.39.2