Add IfElseSwap option

This enables an option that was being done unconditionally: to swap the `if` and `else` branches if the condition is shorter when negated.

Enabled by default.

lslopt/lslfoldconst.py

@@ -1796,7 +1796,7 @@ class foldconst(object):
                     self.FoldTree(child, 2)
                     self.FoldStmt(child, 2)
                     # Check if it makes sense to swap if and else branches
-                    if not child[2].SEF:
+                    if self.ifelseswap and not child[2].SEF:
                         # Check if we can gain something by negating the
                         # expression.
                         # Swap 'if' and 'else' branch when the condition has

lslopt/lsloptimizer.py

@@ -68,6 +68,7 @@ class optimizer(foldconst, renamer, deadcode, lastpass):
         self.shrinknames = 'shrinknames' in options
 
         self.constfold = 'constfold' in options
+        self.ifelseswap = 'ifelseswap' in options
         self.optlistlength = 'listlength' in options
         self.optlistadd = 'listadd' in options
         self.dcr = 'dcr' in options

main.py

@@ -326,6 +326,9 @@ Case insensitive.
   OptFloats          + Optimize floats that represent an integral value.
   ConstFold          + Fold constant expressions to their values, and simplify
                        some expressions and statements.
+  IfElseSwap         + In 'if' statements, when negating the condition produces
+                       shorter code, do it and swap the if and else branches.
+                       Requires ConstFold to be enabled.
   DCR                + Dead code removal. This option removes several instances
                        of code that will never execute, and performs other
                        optimizations like removal of unused variables,
@@ -379,9 +382,9 @@ break/continue syntax extension (which is inactive by default).
 validoptions = frozenset({'extendedglobalexpr','breakcont','extendedtypecast',
     'extendedassignment','allowkeyconcat','allowmultistrings','duplabels',
     'lazylists','enableswitch','errmissingdefault','funcoverride','optimize',
-    'optsigns','optfloats','constfold','dcr','shrinknames','addstrings',
-    'foldtabs','warntabs','processpre','explicitcast','listlength','listadd',
-    'inline', 'help',
+    'optsigns','optfloats','constfold','ifelseswap','dcr','shrinknames',
+    'addstrings','foldtabs','warntabs','processpre','explicitcast',
+    'listlength','listadd','inline','help',
     # undocumented
     'lso','expr','rsrclimit',
     # 'clear' is handled as a special case
@@ -396,10 +399,10 @@ def main(argv):
     lslopt.lslcommon.DataPath = __file__[:-len(os.path.basename(__file__))]
 
     # Default options
-    options = set(('extendedglobalexpr','extendedtypecast','extendedassignment',
-        'allowkeyconcat','allowmultistrings','processpre','warntabs','optimize',
-        'optsigns','optfloats','constfold','dcr','errmissingdefault',
-        'listlength','listadd',
+    options = set(('extendedglobalexpr','extendedtypecast',
+        'extendedassignment','allowkeyconcat','allowmultistrings','processpre',
+        'warntabs','optimize','optsigns','optfloats','constfold','ifelseswap',
+        'dcr','errmissingdefault','listlength','listadd',
         ))
 
     assert not (options - validoptions), (u"Default options not present in"

unit_tests/regression.suite/if-else-noswap.lsl

@@ -0,0 +1,7 @@
+default{timer(){
+
+integer a = llGetLinkNumber();
+if (a == 3) llOwnerSay("1"); else llOwnerSay("2");
+if (!a) llOwnerSay("3"); else llOwnerSay("4");
+
+}}

unit_tests/regression.suite/if-else-noswap.out

@@ -0,0 +1,15 @@
+default
+{
+    timer()
+    {
+        integer a = llGetLinkNumber();
+        if (a == 3)
+            llOwnerSay("1");
+        else
+            llOwnerSay("2");
+        if (!a)
+            llOwnerSay("3");
+        else
+            llOwnerSay("4");
+    }
+}

unit_tests/regression.suite/if-else-noswap.run

@@ -0,0 +1 @@
+main.py -O -ifelseswap -

unit_tests/regression.suite/if-stmt.lsl

@@ -17,10 +17,10 @@ if ((key)((string)a)) ; else llDie();
 if (<a,0,0>) ; else llDie();
 if (<a,0,0,1>) ; else llDie();
 if ((list)a) ; else llDie();
-if (!a) llDie(); else llOwnerSay("ok");
-if (a == 3) llDie(); else llOwnerSay("ok");
-if (a > 5) if (a == 12) ; else llDie(); else llOwnerSay("ok");
-if (a == 12) llOwnerSay("1"); else if (a > 5) llOwnerSay("2");
+if (!a) llDie(); else llOwnerSay("1");
+if (a == 3) llDie(); else llOwnerSay("2");
+if (a > 5) if (a == 12) ; else llDie(); else llOwnerSay("3");
+if (a == 12) llOwnerSay("4"); else if (a > 5) llOwnerSay("5");
 if (a > 5) if (a == 12) ; else /*@f1*/; else llDie();
 if (a == 12) llDie(); else if (a > 5) /*@f4*/;
 // Fixed: Regression: this produces if (!(a == 3)) and no optimization kicks in

unit_tests/regression.suite/if-stmt.out

@@ -22,11 +22,11 @@ default
         if ((list)a == [])
             llDie();
         if (a)
-            llOwnerSay("ok");
+            llOwnerSay("1");
         else
             llDie();
         if (a ^ 3)
-            llOwnerSay("ok");
+            llOwnerSay("2");
         else
             llDie();
         if (5 < a)
@@ -35,14 +35,14 @@ default
                 llDie();
         }
         else
-            llOwnerSay("ok");
+            llOwnerSay("3");
         if (a ^ 12)
         {
             if (5 < a)
-                llOwnerSay("2");
+                llOwnerSay("5");
         }
         else
-            llOwnerSay("1");
+            llOwnerSay("4");
         if (a < 6)
             llDie();
         if (a == 12)