beam_makeops: Rewrite the packer, fixing several bugs

The packer had several bugs and limitations. For instance, on
a 32-bit Erlang virtual machine it would gladly pack three
't' values into one word even though it would be not safe.

The rewritten version will be more careful how much it packs
into each word. It will also be able to do packing for more
instructions.

1 files changed, 165 insertions, 94 deletions

diff --git a/erts/emulator/utils/beam_makeops b/erts/emulator/utils/beam_makeops
index 4108138b51..2a957d2c9d 100755
--- a/erts/emulator/utils/beam_makeops
+++ b/erts/emulator/utils/beam_makeops
@@ -54,11 +54,6 @@ $pack_mask[4]  = ['BEAM_LOOSE_MASK', # Only for 64 bit wordsize
 		  'BEAM_LOOSE_MASK',
 		  $WHOLE_WORD];
 
-# Mapping from packagable arguments to number of packed arguments per
-# word.  Initialized after the wordsize is known.
-
-my @args_per_word;
-
 # There are two types of instructions: generic and specific.
 # The generic instructions are those generated by the Beam compiler.
 # Corresponding to each generic instruction, there is generally a
@@ -264,15 +259,8 @@ if ($wordsize == 32) {
 # Initialize number of arguments per packed word.
 #
 
-$args_per_word[2] = 2;
-$args_per_word[3] = 3;
-$args_per_word[4] = 2;
-$args_per_word[5] = 3;
-$args_per_word[6] = 3;
-
 if ($wordsize == 64) {
     $pack_mask[3] = ['BEAM_TIGHT_MASK', 'BEAM_TIGHT_MASK', $WHOLE_WORD];
-    $args_per_word[4] = 4;
 }
 
 #
@@ -1240,7 +1228,7 @@ sub basic_generator {
 
     my $c_code_ref = $c_code{$name};
     if ($hot and defined $c_code_ref) {
-        ($prefix, $pack_spec, @args) = do_pack(@args);
+        ($var_decls, $pack_spec, @args) = do_pack(@args);
     }
 
     #
@@ -1254,7 +1242,14 @@ sub basic_generator {
 	my($this_size) = $arg_size{$_};
       SWITCH:
 	{
-	    /^pack:(\d):(.*)/ and do {
+	    /^packed:d:(\d):(.*)/ and do {
+                $var_decls .= "Eterm dst = $2;\n" .
+                    "Eterm* dst_ptr = REG_TARGET_PTR(dst);\n";
+                push(@f, "*dst_ptr");
+                $this_size = $1;
+                last SWITCH;
+            };
+	    /^packed:[a-zA-z]:(\d):(.*)/ and do {
                 push(@f, $2);
                 $this_size = $1;
                 last SWITCH;
@@ -1458,29 +1453,28 @@ sub expand_macro {
 sub do_pack {
     my(@args) = @_;
     my($packable_args) = 0;
-    my @is_packable;		# Packability (boolean) for each argument.
-    my $wide_packing = 0;
-    my(@orig_args) = @args;
+    my @bits_needed;            # Bits needed for each argument.
 
     #
-    # Count the number of packable arguments.  If we encounter any 's' or 'd'
-    # arguments, packing is not possible.
+    # Define the minimum number of bits needed for the packable argument types.
+    #
+    my %bits_needed = ('x' => 10,
+                       'y' => 10,
+                       'Q' => 10,
+                       'l' => 10,
+                       'd' => 16,
+                       't' => 16);
+    if ($wordsize == 64) {
+        $bits_needed{'I'} = 32;
+    }
+
+    #
+    # Count the number of packable arguments.
     #
-    my $packable_types = "xytQ";
     foreach my $arg (@args) {
-	if ($arg =~ /^[$packable_types]/) {
+        if (defined $bits_needed{$arg}) {
 	    $packable_args++;
-	    push @is_packable, 1;
-	} elsif ($arg =~ /^I/ and $wordsize == 64 and $packable_args < 2) {
-	    $wide_packing = 1;
-	    push @is_packable, 1;
-	    if (++$packable_args == 2) {
-		# We can only pack two arguments. Turn off packing
-		# for the rest of the arguments.
-		$packable_types = "\xFF";
-	    }
-	} elsif ($arg =~ /^[sd]/) {
-	    return ('', '', @args);
+            push @bits_needed, $bits_needed{$arg};
 	} elsif ($arg =~ /^[scq]/ and $packable_args > 0) {
 	    # When packing, this operand will be picked up from the
 	    # code array, put onto the packing stack, and later put
@@ -1494,87 +1488,164 @@ sub do_pack {
 	    # just turn off packing.
 	    return ('', '', @args);
 	} else {
-	    push @is_packable, 0;
+	    push @bits_needed, 0;
 	}
     }
 
     #
-    # Get out of here if too few or too many arguments.
+    # Nothing to pack unless there are at least 2 packable arguments.
     #
     return ('', '', @args) if $packable_args < 2;
 
-    my($size) = 0;
-    my($pack_prefix) = '';
-    my($down) = '';		# Pack commands (towards instruction
+    #
+    # Determine how many arguments we should pack into each word.
+    #
+    my @args_per_word;
+    my @need_wide_mask;
+    my $bits = 0;
+    my $word = 0;
+    $args_per_word[0] = 0;
+    $need_wide_mask[0] = 0;
+    for (my $i = 0; $i < @args; $i++) {
+        if ($bits_needed[$i]) {
+            my $needed = $bits_needed[$i];
+
+            my $next_word = sub {
+                $word++;
+                $args_per_word[$word] = 0;
+                $need_wide_mask[$word] = 0;
+                $bits = 0;
+            };
+
+            if ($bits+$needed > $wordsize) { # Does not fit.
+                $next_word->();
+            }
+            if ($args_per_word[$word] == 4) { # Can't handle more than 4 args.
+                $next_word->();
+            }
+            if ($needed == 32 and $args_per_word[$word] > 1) {
+                # Must only pack two arguments in this word, and there
+                # are already at least two arguments here.
+                $next_word->();
+            }
+            $args_per_word[$word]++;
+            $bits += $needed;
+            if ($needed == 32) {
+                $need_wide_mask[$word]++;
+            }
+            if ($need_wide_mask[$word] and $bits > 32) {
+                # Can only pack two things in a word where one
+                # item is 32 bits. Force the next item into
+                # the next word.
+                $bits = $wordsize;
+            }
+        }
+    }
+
+    #
+    # Try to balance packing between words.
+    #
+    if ($args_per_word[$#args_per_word] == 1) {
+        if ($args_per_word[$#args_per_word-1] < 3) {
+            pop @args_per_word;
+        } else {
+            $args_per_word[$#args_per_word-1]--;
+            $args_per_word[$#args_per_word]++;
+        }
+    } elsif (@args_per_word == 2 and
+             $args_per_word[0] == 4 and
+             $args_per_word[1] == 2) {
+        $args_per_word[0] = 3;
+        $args_per_word[1] = 3;
+    } elsif (@args_per_word == 2 and
+             $args_per_word[0] == 3 and
+             $args_per_word[1] == 1) {
+        $args_per_word[0] = 2;
+        $args_per_word[1] = 2;
+    }
+
+    my $size = 0;
+    my $pack_prefix = '';
+    my $down = '';		# Pack commands (towards instruction
 				# beginning).
-    my($up) = '';		# Pack commands (storing back while
+    my $up = '';		# Pack commands (storing back while
 				# moving forward).
+    my $did_some_packing = 0;   # Nothing packed yet.
 
-    my $args_per_word = $args_per_word[$packable_args];
-    my @shift;
-    my @mask;
-    my @instr;
+    # Skip an unpackable argument.
+    my $skip_unpackable = sub {
+        my($arg) = @_;
 
-    if ($wide_packing) {
-	@shift = ('0', 'BEAM_WIDE_SHIFT');
-	@mask = ('BEAM_WIDE_MASK', $WHOLE_WORD);
-	@instr = ('w', 'i');
-    } else {
-	@shift = @{$pack_shift[$args_per_word]};
-	@mask = @{$pack_mask[$args_per_word]};
-	@instr = @{$pack_instr[$args_per_word]};
-    }
+        if ($arg_size{$arg} and $did_some_packing) {
+            # Save the argument on the pack engine's stack.
+            $down = "g${down}";
+            $up = "${up}p";
+        } else {
+            # The argument has either zero size (e.g. r(0)),
+            # or is to the left of the first packed argument
+            # and will never be accessed. No need to do
+            # anything.
+        }
+    };
 
     #
     # Now generate the packing instructions.  One complication is that
     # the packing engine works from right-to-left, but we must generate
     # the instructions from left-to-right because we must calculate
     # instruction sizes from left-to-right.
-    #
-    # XXX Packing 3 't's in one word won't work.  Sorry.
 
-    my $did_some_packing = 0;	# Nothing packed yet.
-    my($ap) = 0;		# Argument number within word.
-    my($tmpnum) = 1;		# Number of temporary variable.
-    my($expr) = '';
-    for (my $i = 0; $i < @args; $i++) {
-	my($reg) = $args[$i];
-	my($this_size) = $arg_size{$reg};
-	if ($is_packable[$i]) {
-	    $this_size = 0;
-	    $did_some_packing = 1;
-
-	    if ($ap == 0) {
-		$pack_prefix .= "Eterm tmp_packed$tmpnum = Arg($size);\n";
-		$up .= "p";
-		$down = "P$down";
-		$this_size = 1;
-	    }
+    my $arg_num = 0;
+    for (my $word = 0; $word < @args_per_word; $word++) {
+        my $ap = 0;              # Argument number within word.
+        my $packed_var = "tmp_packed" . ($word+1);
+        my $args_per_word = $args_per_word[$word];
+        my @shift;
+        my @mask;
+        my @instr;
+
+        if ($need_wide_mask[$word]) {
+            @shift = ('0', 'BEAM_WIDE_SHIFT');
+            @mask = ('BEAM_WIDE_MASK', $WHOLE_WORD);
+            @instr = ('w', 'i');
+        } else {
+            @shift = @{$pack_shift[$args_per_word]};
+            @mask = @{$pack_mask[$args_per_word]};
+            @instr = @{$pack_instr[$args_per_word]};
+        }
 
-	    $down = "$instr[$ap]$down";
-	    my($unpack) = make_unpack($tmpnum, $shift[$ap], $mask[$ap]);
-	    $args[$i] = "pack:$this_size:$reg" . "b($unpack)";
+        while ($ap < $args_per_word) {
+            my $reg = $args[$arg_num];
+            my $this_size = $arg_size{$reg};
+            if ($bits_needed[$arg_num]) {
+                $this_size = 0;
+                $did_some_packing = 1;
+
+                if ($ap == 0) {
+                    $pack_prefix .= "Eterm $packed_var = Arg($size);\n";
+                    $up .= "p";
+                    $down = "P$down";
+                    $this_size = 1;
+                }
 
-	    if (++$ap == $args_per_word) {
-		$ap = 0;
-		$tmpnum++;
-	    }
-	} elsif ($arg_size{$reg} && $did_some_packing) {
-	    #
-	    # This is an argument that can't be packed.  Normally, we must
-	    # save it on the pack engine's stack, unless:
-	    #
-	    # 1. The argument has zero size (e.g. r(0)).  Such arguments
-	    #    will not be loaded.  They disappear.
-	    # 2. If the argument is on the left of the first packed argument,
-	    #    the packing engine will never access it (because the engine
-	    #    operates from right-to-left).
-	    #
+                $down = "$instr[$ap]$down";
+                my $unpack = make_unpack($packed_var, $shift[$ap], $mask[$ap]);
+                $args[$arg_num] = "packed:$reg:$this_size:$reg" . "b($unpack)";
 
-	    $down = "g${down}";
-	    $up = "${up}p";
-	}
-	$size += $this_size;
+                $ap++;
+            } else {
+                $skip_unpackable->($reg);
+            }
+            $size += $this_size;
+            $arg_num++;
+        }
+    }
+
+    #
+    # Skip any unpackable arguments at the end.
+    #
+    while ($arg_num < @args) {
+        $skip_unpackable->($args[$arg_num]);
+        $arg_num++;
     }
 
     my $pack_spec = $down . $up;
@@ -1582,9 +1653,9 @@ sub do_pack {
 }
 
 sub make_unpack {
-    my($tmpnum, $shift, $mask) = @_;
+    my($packed_var, $shift, $mask) = @_;
 
-    my($e) = "tmp_packed$tmpnum";
+    my $e = $packed_var;
     $e = "($e>>$shift)" if $shift;
     $e .= "&$mask" unless $mask eq $WHOLE_WORD;
     $e;