#!/usr/bin/env perl

  # SPDX-License-Identifier: GPL-2.0

  
  # Read two files produced by the stackusage script, and show the
  # delta between them.
  #
  # Currently, only shows changes for functions listed in both files. We
  # could add an option to show also functions which have vanished or
  # appeared (which would often be due to gcc making other inlining
  # decisions).
  #
  # Another possible option would be a minimum absolute value for the
  # delta.
  #
  # A third possibility is for sorting by delta, but that can be
  # achieved by piping to sort -k5,5g.
  
  sub read_stack_usage_file {
      my %su;
      my $f = shift;
      open(my $fh, '<', $f)
  	or die "cannot open $f: $!";
      while (<$fh>) {
  	chomp;
  	my ($file, $func, $size, $type) = split;
  	# Old versions of gcc (at least 4.7) have an annoying quirk in
  	# that a (static) function whose name has been changed into
  	# for example ext4_find_unwritten_pgoff.isra.11 will show up
  	# in the .su file with a name of just "11". Since such a
  	# numeric suffix is likely to change across different
  	# commits/compilers/.configs or whatever else we're trying to
  	# tweak, we can't really track those functions, so we just
  	# silently skip them.
  	#
  	# Newer gcc (at least 5.0) report the full name, so again,
  	# since the suffix is likely to change, we strip it.
  	next if $func =~ m/^[0-9]+$/;
  	$func =~ s/\..*$//;
  	# Line numbers are likely to change; strip those.
  	$file =~ s/:[0-9]+$//;
  	$su{"${file}\t${func}"} = {size => $size, type => $type};
      }
      close($fh);
      return \%su;
  }
  
  @ARGV == 2
      or die "usage: $0 <old> <new>";
  
  my $old = read_stack_usage_file($ARGV[0]);
  my $new = read_stack_usage_file($ARGV[1]);
  my @common = sort grep {exists $new->{$_}} keys %$old;
  for (@common) {
      my $x = $old->{$_}{size};
      my $y = $new->{$_}{size};
      my $delta = $y - $x;
      if ($delta) {
  	printf "%s\t%d\t%d\t%+d
  ", $_, $x, $y, $delta;
      }
  }