Re: Scrolling huge buffers and cc-mode

[Dmitry Antipov]

It looks like the reason of slow scrolling is how the C++ namespaces are 
handled.

Basically my test file is:

namespace X {
namespace Y {

/* 13K lines of code */

} }

/* middle-point */

namespace X {
namespace Y {

/* 13K lines of code */

} }

When scrolling reaches middle-point, everything hangs, most probably because
we need to scan huge regions (first and second namespace blocks). When I remove
all namespace definitions (with matched '}'), scrolling works much faster.
Corresponding profile is:

    13.04%        emacs  emacs                          [.] mark_object
     7.70%        emacs  emacs                          [.] exec_byte_code
     6.79%        emacs  emacs                          [.] re_match_2_internal
     6.48%        emacs  emacs                          [.] lookup_char_property
     4.70%        emacs  emacs                          [.] scan_sexps_forward
     4.67%        emacs  emacs                          [.] Fgarbage_collect
     4.62%        emacs  emacs                          [.] re_compile_pattern
     4.57%        emacs  emacs                          [.] next_interval
     3.29%        emacs  emacs                          [.] find_interval
     3.16%        emacs  emacs                          [.] mark_interval
     2.15%        emacs  emacs                          [.] Fcdr
     2.06%        emacs  emacs                          [.] update_syntax_table
     1.83%        emacs  emacs                          [.] Flocal_variable_p
     1.33%        emacs  emacs                          [.] Fassq
     1.19%        emacs  emacs                          [.] 
balance_intervals_internal
     1.13%        emacs  emacs                          [.] Ffuncall
     1.00%        emacs  emacs                          [.] compile_pattern

This is very similar to what I'm seeing while scrolling over xdisp.c:

    13.92%        emacs  emacs                          [.] mark_object
     8.20%        emacs  emacs                          [.] exec_byte_code
     4.91%        emacs  emacs                          [.] re_match_2_internal
     4.78%        emacs  emacs                          [.] Fgarbage_collect
     4.65%        emacs  emacs                          [.] lookup_char_property
     3.60%        emacs  emacs                          [.] find_interval
     3.55%        emacs  emacs                          [.] scan_sexps_forward
     3.45%        emacs  emacs                          [.] re_compile_pattern
     2.77%        emacs  emacs                          [.] Flocal_variable_p
     2.71%        emacs  emacs                          [.] mark_interval
     2.46%        emacs  emacs                          [.] next_interval
     1.62%        emacs  emacs                          [.] update_syntax_table
     1.52%        emacs  emacs                          [.] Fassq
     1.45%        emacs  emacs                          [.] Fcdr
     1.35%        emacs  emacs                          [.] Ffuncall
     1.11%        emacs  emacs                          [.] compile_pattern

Dmitry