merge branch 'if-no-waste'

hy/compiler.py

@@ -377,6 +377,7 @@ class HyASTCompiler(object):
         self.anon_var_count = 0
         self.imports = defaultdict(set)
         self.module_name = module_name
+        self.temp_if = None
         if not module_name.startswith("hy.core"):
             # everything in core needs to be explicit.
             load_stdlib()
@@ -1003,11 +1004,41 @@ class HyASTCompiler(object):
     def compile_if(self, expression):
         expression.pop(0)
         cond = self.compile(expression.pop(0))
-
         body = self.compile(expression.pop(0))
+
         orel = Result()
+        nested = root = False
         if expression:
-            orel = self.compile(expression.pop(0))
+            orel_expr = expression.pop(0)
+            if isinstance(orel_expr, HyExpression) and isinstance(orel_expr[0],
+               HySymbol) and orel_expr[0] == 'if':
+                # Nested ifs: don't waste temporaries
+                root = self.temp_if is None
+                nested = True
+                self.temp_if = self.temp_if or self.get_anon_var()
+            orel = self.compile(orel_expr)
+
+        if not cond.stmts and isinstance(cond.force_expr, ast.Name):
+            name = cond.force_expr.id
+            branch = None
+            if name == 'True':
+                branch = body
+            elif name in ('False', 'None'):
+                branch = orel
+            if branch is not None:
+                if self.temp_if and branch.stmts:
+                    name = ast.Name(id=ast_str(self.temp_if),
+                                    arg=ast_str(self.temp_if),
+                                    ctx=ast.Store(),
+                                    lineno=expression.start_line,
+                                    col_offset=expression.start_column)
+
+                    branch += ast.Assign(targets=[name],
+                                         value=body.force_expr,
+                                         lineno=expression.start_line,
+                                         col_offset=expression.start_column)
+
+                return branch
 
         # We want to hoist the statements from the condition
         ret = cond
@@ -1015,7 +1046,7 @@ class HyASTCompiler(object):
         if body.stmts or orel.stmts:
             # We have statements in our bodies
             # Get a temporary variable for the result storage
-            var = self.get_anon_var()
+            var = self.temp_if or self.get_anon_var()
             name = ast.Name(id=ast_str(var), arg=ast_str(var),
                             ctx=ast.Store(),
                             lineno=expression.start_line,
@@ -1028,6 +1059,8 @@ class HyASTCompiler(object):
                                col_offset=expression.start_column)
 
             # and of the else clause
+            if not nested or not orel.stmts or (not root and
+               var != self.temp_if):
                 orel += ast.Assign(targets=[name],
                                    value=orel.force_expr,
                                    lineno=expression.start_line,
@@ -1054,6 +1087,10 @@ class HyASTCompiler(object):
                              orelse=orel.force_expr,
                              lineno=expression.start_line,
                              col_offset=expression.start_column)
+
+        if root:
+            self.temp_if = None
+
         return ret
 
     @builds("break")