Optimize away control exception handlers in while/unit/repeat loops that don't need them.

Author: jnthn

src/NQP/Actions.pm

@@ -339,6 +339,9 @@ class NQP::Actions is HLL::Actions {
     method statement_control:sym<while>($/) {
         my $past := xblock_immediate( $<xblock>.ast );
         $past.op(~$<sym>);
+        unless $*CONTROL_USED {
+            $past.push(QAST::IVal.new( :value(1), :named('nohandler') ));
+        }
         make $past;
     }
 
@@ -353,6 +356,9 @@ class NQP::Actions is HLL::Actions {
             $past := QAST::Op.new( $<EXPR>.ast, block_immediate( $<pblock>.ast ),
                                    :op($op), :node($/) );
         }
+        unless $*CONTROL_USED {
+            $past.push(QAST::IVal.new( :value(1), :named('nohandler') ));
+        }
         make $past;
     }
 

src/NQP/Grammar.pm

@@ -24,11 +24,12 @@ grammar NQP::Grammar is HLL::Grammar {
             NQP::World.new(:handle($source_id)) !!
             NQP::World.new(:handle($source_id), :description($file));
 
-        my $*SCOPE       := '';
-        my $*MULTINESS   := '';
-        my $*PKGDECL     := '';
-        my $*INVOCANT_OK := 0;
-        my $*RETURN_USED := 0;
+        my $*SCOPE        := '';
+        my $*MULTINESS    := '';
+        my $*PKGDECL      := '';
+        my $*INVOCANT_OK  := 0;
+        my $*RETURN_USED  := 0;
+        my $*CONTROL_USED := 0;
         my %*HANDLERS;
         self.comp_unit;
     }
@@ -211,11 +212,13 @@ grammar NQP::Grammar is HLL::Grammar {
     }
 
     token statement_control:sym<while> {
+        :my $*CONTROL_USED := 0;
         $<sym>=[while|until] \s :s
         <xblock>
     }
 
     token statement_control:sym<repeat> {
+        :my $*CONTROL_USED := 0;
         <sym> \s :s
         [
         | $<wu>=[while|until]\s <xblock>
@@ -730,9 +733,9 @@ grammar NQP::Grammar is HLL::Grammar {
 
     token prefix:sym<return> { <sym> \s <O('%list_prefix')> { $*RETURN_USED := 1 } }
     token prefix:sym<make>   { <sym> \s <O('%list_prefix')> }
-    token term:sym<last>     { <sym> }
-    token term:sym<next>     { <sym> }
-    token term:sym<redo>     { <sym> }
+    token term:sym<last>     { <sym> { $*CONTROL_USED := 1 } }
+    token term:sym<next>     { <sym> { $*CONTROL_USED := 1 } }
+    token term:sym<redo>     { <sym> { $*CONTROL_USED := 1 } }
 
     method smartmatch($/) {
         # swap rhs into invocant position

src/QAST/Operations.nqp

@@ -612,6 +612,9 @@ for ('', 'repeat_') -> $repness {
                 $ops.push($done_lbl);
                 $ops.push_pirop('pop_eh');
             }
+            else {
+                $ops.push($done_lbl);
+            }
 
             $ops;
         });

src/QRegex/Cursor.nqp

@@ -182,6 +182,7 @@ role NQPCursorRole {
             if !nqp::isnull($actions) && nqp::can($actions, $name);
     }
 
+    my @EMPTY := [];
     method !protoregex($name) {
         # Obtain and run NFA.
         my $nfa := self.HOW.cache(self, $name, { self.'!protoregex_nfa'($name) });
@@ -195,7 +196,7 @@ role NQPCursorRole {
             $rxname := nqp::atpos(@rxfate, nqp::pop_i(@fates));
             #nqp::say("invoking $rxname");
             $cur := self."$rxname"();
-            last if nqp::getattr_i($cur, $?CLASS, '$!pos') >= 0;
+            @fates := @EMPTY if nqp::getattr_i($cur, $?CLASS, '$!pos') >= 0;
         }
         $cur // self."!cursor_start"();
     }