Eliminate prefetch for conditional instructions

Not pre-fetching in conditional instructions (instructions that use
-fail_action) seems to improve performance slightly.

The reason for that is that conditional instructions may jump to the
failure label, wasting the pre-fetched instruction. Another reason
is that that many conditional instructions do a function call, and
the register pressure is therefore high. Avoiding the pre-fetch
may reduce the register pressure and pontentially result in more
efficient code.

2 files changed, 9 insertions, 1 deletions

diff --git a/erts/emulator/beam/ops.tab b/erts/emulator/beam/ops.tab
index bce6bacd5c..3d52da77d3 100644
--- a/erts/emulator/beam/ops.tab
+++ b/erts/emulator/beam/ops.tab
@@ -477,7 +477,7 @@ i_is_ne_exact_literal f x c
 i_is_ne_exact_literal f y c
 
 is_eq_exact Lbl Y=y X=x => is_eq_exact Lbl X Y
-%macro: is_eq_exact EqualExact -fail_action
+%macro: is_eq_exact EqualExact -fail_action -pack
 is_eq_exact f x x
 is_eq_exact f x y
 is_eq_exact f s s
diff --git a/erts/emulator/utils/beam_makeops b/erts/emulator/utils/beam_makeops
index 44977ecffc..06515c6346 100755
--- a/erts/emulator/utils/beam_makeops
+++ b/erts/emulator/utils/beam_makeops
@@ -917,6 +917,7 @@ sub basic_generator {
     my($var_decls) = '';
     my($gen_dest_arg) = 'StoreSimpleDest';
     my($i);
+    my($no_prefetch) = 0;
 
     # The following argument types should be included as macro arguments.
     my(%incl_arg) = ('c' => 1,
@@ -1015,6 +1016,7 @@ sub basic_generator {
     #
 
     $flags =~ /-fail_action/ and do {
+	$no_prefetch = 1;
 	if (!defined $fail_type) {
 	    my($i);
 	    for ($i = 0; $i < @f_types; $i++) {
@@ -1061,6 +1063,12 @@ sub basic_generator {
 			 "I += $size + 1;",
 			 "goto $goto;",
 			 "}");
+	} elsif ($no_prefetch) {
+	    $code = join("\n",
+			 "{ $var_decls",
+			 $macro_code,
+			 "Next($size);",
+			 "}", "");
 	} else {
 	    $code = join("\n",
 			 "{ $var_decls",