PR30724, cygwin ld performance regression since 014a602b86

According to the reporter of this bug the newlib fseek implementation
is likely slowed down by locking and fflush, only attempting to
optimise seeks when the file is opened read-only.  Thus when writing
the output we get a dramatic slowdown due to commit 014a602b86.

	PR 30724
	* bfd.c (enum bfd_last_io): New.
	(struct bfd): Add last_io field.
	* bfd-in2.h: Regenerate.
	* bfd-io.c (bfd_bread, bfd_bwrite): Force seek if last_io is
	opposite direction.
	(bfd_seek): Reinstate optimisation for seek to same position.

diff --git a/bfd/bfd-in2.h b/bfd/bfd-in2.h
index 5f49807d7f20e7ec2ab5b8db8b9b7ec7ee91997a..cc62ab196176b2115ab9d46d327d8790ebc29a09 100644 (file)
--- a/bfd/bfd-in2.h
+++ b/bfd/bfd-in2.h
@@ -1916,6 +1916,14 @@ enum bfd_direction
     both_direction = 3
   };
 
+enum bfd_last_io
+  {
+    bfd_io_seek = 0,
+    bfd_io_read = 1,
+    bfd_io_write = 2,
+    bfd_io_force = 3
+  };
+
 enum bfd_plugin_format
   {
     bfd_plugin_unknown = 0,
@@ -2068,6 +2076,20 @@ struct bfd
   /* The direction with which the BFD was opened.  */
   ENUM_BITFIELD (bfd_direction) direction : 2;
 
+  /* POSIX.1-2017 (IEEE Std 1003.1) says of fopen : "When a file is
+     opened with update mode ('+' as the second or third character in
+     the mode argument), both input and output may be performed on
+     the associated stream.  However, the application shall ensure
+     that output is not directly followed by input without an
+     intervening call to fflush() or to a file positioning function
+     (fseek(), fsetpos(), or rewind()), and input is not directly
+     followed by output without an intervening call to a file
+     positioning function, unless the input operation encounters
+     end-of-file."
+     This field tracks the last IO operation, so that bfd can insert
+     a seek when IO direction changes.  */
+  ENUM_BITFIELD (bfd_last_io) last_io : 2;
+
   /* Is the file descriptor being cached?  That is, can it be closed as
      needed, and re-opened when accessed later?  */
   unsigned int cacheable : 1;

diff --git a/bfd/bfd.c b/bfd/bfd.c
index e43a388ac721fbdb01a6344c84f4c7f240e5a5dd..88943a042d661373f6fc6d4472974fdc32c854c2 100644 (file)
--- a/bfd/bfd.c
+++ b/bfd/bfd.c
@@ -53,6 +53,14 @@ EXTERNAL
 .    both_direction = 3
 .  };
 .
+.enum bfd_last_io
+.  {
+.    bfd_io_seek = 0,
+.    bfd_io_read = 1,
+.    bfd_io_write = 2,
+.    bfd_io_force = 3
+.  };
+.
 .enum bfd_plugin_format
 .  {
 .    bfd_plugin_unknown = 0,
@@ -208,6 +216,20 @@ CODE_FRAGMENT
 .  {* The direction with which the BFD was opened.  *}
 .  ENUM_BITFIELD (bfd_direction) direction : 2;
 .
+.  {* POSIX.1-2017 (IEEE Std 1003.1) says of fopen : "When a file is
+.     opened with update mode ('+' as the second or third character in
+.     the mode argument), both input and output may be performed on
+.     the associated stream.  However, the application shall ensure
+.     that output is not directly followed by input without an
+.     intervening call to fflush() or to a file positioning function
+.     (fseek(), fsetpos(), or rewind()), and input is not directly
+.     followed by output without an intervening call to a file
+.     positioning function, unless the input operation encounters
+.     end-of-file."
+.     This field tracks the last IO operation, so that bfd can insert
+.     a seek when IO direction changes.  *}
+.  ENUM_BITFIELD (bfd_last_io) last_io : 2;
+.
 .  {* Is the file descriptor being cached?  That is, can it be closed as
 .     needed, and re-opened when accessed later?  *}
 .  unsigned int cacheable : 1;

diff --git a/bfd/bfdio.c b/bfd/bfdio.c
index 22c39a7b0ccfb0bd9ef29cea58ce1d699dec9d45..e0d47b3ee1c3017f1bf45e3f5187251d8cff0500 100644 (file)
--- a/bfd/bfdio.c
+++ b/bfd/bfdio.c
@@ -279,6 +279,14 @@ bfd_bread (void *ptr, bfd_size_type size, bfd *abfd)
       return -1;
     }
 
+  if (abfd->last_io == bfd_io_write)
+    {
+      abfd->last_io = bfd_io_force;
+      if (bfd_seek (abfd, 0, SEEK_CUR) != 0)
+       return -1;
+    }
+  abfd->last_io = bfd_io_read;
+
   nread = abfd->iovec->bread (abfd, ptr, size);
   if (nread != -1)
     abfd->where += nread;
@@ -313,6 +321,14 @@ bfd_bwrite (const void *ptr, bfd_size_type size, bfd *abfd)
       return -1;
     }
 
+  if (abfd->last_io == bfd_io_read)
+    {
+      abfd->last_io = bfd_io_force;
+      if (bfd_seek (abfd, 0, SEEK_CUR) != 0)
+       return -1;
+    }
+  abfd->last_io = bfd_io_write;
+
   nwrote = abfd->iovec->bwrite (abfd, ptr, size);
   if (nwrote != -1)
     abfd->where += nwrote;
@@ -456,6 +472,13 @@ bfd_seek (bfd *abfd, file_ptr position, int direction)
   if (direction != SEEK_CUR)
     position += offset;
 
+  if (((direction == SEEK_CUR && position == 0)
+       || (direction == SEEK_SET && (ufile_ptr) position == abfd->where))
+      && abfd->last_io != bfd_io_force)
+    return 0;
+
+  abfd->last_io = bfd_io_seek;
+
   result = abfd->iovec->bseek (abfd, position, direction);
   if (result != 0)
     {