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authorBjörn Gustavsson <[email protected]>2016-04-04 15:37:46 +0200
committerBjörn Gustavsson <[email protected]>2016-04-07 15:28:29 +0200
commit72bec464764c919cbfbd2db1c86cce227b2b9c42 (patch)
tree704776bdbae98e3ec6b01150e374cf0ac2ee1933
parent937f527054f13dd524588c064cd5d76e3cfd23eb (diff)
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Remove unused variables after code generation
The removal of instructions on the left side of a transformation is done while generating the code for the left side. Postpone removal of unused variables to a later, separate passes to allow more variables to be eliminated after the optimizations passes introduced in the previous commits.
-rwxr-xr-xerts/emulator/utils/beam_makeops123
1 files changed, 73 insertions, 50 deletions
diff --git a/erts/emulator/utils/beam_makeops b/erts/emulator/utils/beam_makeops
index 66ffd83ee9..2e7073a8f0 100755
--- a/erts/emulator/utils/beam_makeops
+++ b/erts/emulator/utils/beam_makeops
@@ -1402,8 +1402,7 @@ sub tr_gen {
foreach $ref (@g) {
my($line, $orig_transform, $from_ref, $to_ref) = @$ref;
- my $used_ref = used_vars($from_ref, $to_ref);
- my $so_far = tr_gen_from($line, $used_ref, @$from_ref);
+ my $so_far = tr_gen_from($line, @$from_ref);
tr_gen_to($line, $orig_transform, $so_far, @$to_ref);
}
@@ -1454,55 +1453,14 @@ sub tr_gen {
print "};\n\n";
}
-sub used_vars {
- my($from_ref,$to_ref) = @_;
- my %used;
- my %seen;
-
- foreach my $ref (@$from_ref) {
- my($name,$arity,@ops) = @$ref;
- if ($name =~ /^[.]/) {
- foreach my $var (@ops) {
- $used{$var} = 1;
- }
- } else {
- # Any variable that is used at least twice on the
- # left-hand side is used. (E.g. "move R R".)
- foreach my $op (@ops) {
- my($var, $type, $type_val) = @$op;
- next if $var eq '';
- $used{$var} = 1 if $seen{$var};
- $seen{$var} = 1;
- }
- }
- }
-
- foreach my $ref (@$to_ref) {
- my($name, $arity, @ops) = @$ref;
- if ($name =~ /^[.]/) {
- foreach my $var (@ops) {
- $used{$var} = 1;
- }
- } else {
- foreach my $op (@ops) {
- my($var, $type, $type_val) = @$op;
- next if $var eq '';
- $used{$var} = 1;
- }
- }
- }
- \%used;
-}
-
sub tr_gen_from {
- my($line,$used_ref,@tr) = @_;
+ my($line,@tr) = @_;
my(%var) = ();
my(%var_type);
my($var_num) = 0;
my(@code);
my($op, $ref); # Loop variables.
my $where = "left side of transformation in line $line: ";
- my %var_used = %$used_ref;
my $may_fail = 0;
my $is_first = 1;
@@ -1534,7 +1492,10 @@ sub tr_gen_from {
}
}
my $pi = tr_next_index(\@pred_table, \%pred_table, $name, @args);
- push(@code, make_op("$name()", 'pred', $pi));
+ my $op = make_op("$name()", 'pred', $pi);
+ my @slots = grep(/^\d+/, map { $var{$_} } @ops);
+ op_slot_usage($op, @slots);
+ push(@code, $op);
next;
}
@@ -1595,7 +1556,9 @@ sub tr_gen_from {
if (defined $var{$var}) {
$ignored_var = '';
$may_fail = 1;
- push(@code, &make_op($var, 'is_same_var', $var{$var}));
+ my $op = make_op($var, 'is_same_var', $var{$var});
+ op_slot_usage($op, $var{$var});
+ push(@code, $op);
} elsif ($type eq '*') {
foreach my $type (values %var_type) {
error("only one use of a '*' variable is " .
@@ -1607,7 +1570,7 @@ sub tr_gen_from {
$var{$var} = 'unnumbered';
$var_type{$var} = 'array';
push(@code, make_op($var, 'rest_args'));
- } elsif ($var_used{$var}) {
+ } else {
$ignored_var = '';
$var_type{$var} = 'scalar';
$var{$var} = $var_num;
@@ -1677,7 +1640,10 @@ sub tr_gen_to {
pop(@code); # Get rid of 'commit' instruction
my $index = tr_next_index(\@call_table, \%call_table,
$name, @args);
- push(@code, make_op("$name()", 'call_end', $index));
+ my $op = make_op("$name()", 'call_end', $index);
+ my @slots = grep(/^\d+/, map { $var{$_} } @ops);
+ op_slot_usage($op, @slots);
+ push(@code, $op);
last;
}
@@ -1703,7 +1669,9 @@ sub tr_gen_to {
} elsif ($var ne '') {
&error($where, "variable '$var' unbound")
unless defined $var{$var};
- push(@code, &make_op($var, 'store_var_next_arg', $var{$var}));
+ my $op = make_op($var, 'store_var_next_arg', $var{$var});
+ op_slot_usage($op, $var{$var});
+ push(@code, $op);
} elsif ($type ne '') {
push(@code, &make_op('', 'store_type', "TAG_$type"));
if ($type_val) {
@@ -1720,6 +1688,7 @@ sub tr_gen_to {
tr_maybe_keep(\@code);
tr_maybe_rename(\@code);
+ tr_remove_unused(\@code);
#
# Chain together all codes segments having the same first operation.
@@ -1839,6 +1808,55 @@ sub tr_maybe_rename {
}
}
+sub tr_remove_unused {
+ my($ref) = @_;
+ my %used;
+
+ # Collect all used variables.
+ for my $instr (@$ref) {
+ my $uref = $$instr[3];
+ for my $slot (@$uref) {
+ $used{$slot} = 1;
+ }
+ }
+
+ # Replace 'set_var_next_arg' with 'next_arg' if the variable
+ # is never used.
+ for my $instr (@$ref) {
+ my($size, $instr_ref, $comment) = @$instr;
+ my($op, @args) = @$instr_ref;
+ if ($op eq 'set_var_next_arg') {
+ my $var = $args[0];
+ next if $used{$var};
+ $instr = make_op("$comment (ignored)", 'next_arg');
+ }
+ }
+
+ # Delete a sequence of 'next_arg' instructions when they are
+ # redundant before instructions such as 'commit'.
+ my @opcode;
+ my %ending = (call_end => 1,
+ commit => 1,
+ next_instr => 1,
+ pred => 1,
+ rename => 1,
+ keep => 1);
+ for (my $i = 0; $i < @$ref; $i++) {
+ my $instr = $$ref[$i];
+ my($size, $instr_ref, $comment) = @$instr;
+ my($opcode) = @$instr_ref;
+
+ if ($ending{$opcode}) {
+ my $first = $i;
+ $first-- while $first > 0 and $opcode[$first-1] eq 'next_arg';
+ my $n = $i - $first;
+ splice @$ref, $first, $n;
+ $i -= $n;
+ }
+ $opcode[$i] = $opcode;
+ }
+}
+
sub tr_code_len {
my($sum) = 0;
my($ref);
@@ -1851,7 +1869,12 @@ sub tr_code_len {
sub make_op {
my($comment, @op) = @_;
- [scalar(@op), [@op], $comment];
+ [scalar(@op), [@op], $comment, []];
+}
+
+sub op_slot_usage {
+ my($op_ref, @slots) = @_;
+ $$op_ref[3] = \@slots;
}
sub is_instr {