[binutils-gdb/binutils-2_41-branch] PR30724, cygwin ld performance regression since 014a602b86

[binutils-gdb/binutils-2_41-branch] PR30724, cygwin ld performance regression since 014a602b86

[Alan Modra]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=226f2e6b924612ecbdb7dfe4f3ca611116ed77f4

commit 226f2e6b924612ecbdb7dfe4f3ca611116ed77f4
Author: Alan Modra <amodra@gmail.com>
Date:   Mon Aug 7 08:28:55 2023 +0930

    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.
    
    (cherry picked from commit f82ee0c8dc4ee32556e23e6cd83ef083618f704f)

Diff:
---
 bfd/bfd-in2.h | 22 ++++++++++++++++++++++
 bfd/bfd.c     | 22 ++++++++++++++++++++++
 bfd/bfdio.c   | 23 +++++++++++++++++++++++
 3 files changed, 67 insertions(+)

diff --git a/bfd/bfd-in2.h b/bfd/bfd-in2.h
index b34c8ef9fc9..4128972fe49 100644
--- a/bfd/bfd-in2.h
+++ b/bfd/bfd-in2.h
@@ -1913,6 +1913,14 @@ 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,
@@ -2065,6 +2073,20 @@ 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 e43a388ac72..88943a042d6 100644
--- 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 22c39a7b0cc..e0d47b3ee1c 100644
--- 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)
     {