Change semantics of break with no value

break statements without a value will now generate their value from the
else branch of the loop instead of being implict break None.

The for loop has been changed. It will now break out of the loop
instead of continuing with the following iterations if Iterator.next
errors. This is for performance reasons with range check elimination.

Closes ponylang#1156.

Author: Benoit Vey

CHANGELOG.md

@@ -14,6 +14,9 @@ All notable changes to the Pony compiler and standard library will be documented
 
 ### Changed
 
+- `break` without a value now generates its value from the `else` branch of a loop instead of being an implicit `break None`.
+- The `for` loop will now break out of the loop instead of continuing with the following iterations if `Iterator.next` errors.
+
 ## [0.6.0] - 2016-10-20
 
 ### Fixed

src/libponyc/codegen/codegen.c

@@ -970,6 +970,7 @@ void codegen_pushscope(compile_t* c, ast_t* ast)
 
   frame->fun = frame->prev->fun;
   frame->break_target = frame->prev->break_target;
+  frame->break_novalue_target = frame->prev->break_novalue_target;
   frame->continue_target = frame->prev->continue_target;
   frame->invoke_target = frame->prev->invoke_target;
   frame->di_file = frame->prev->di_file;
@@ -1065,12 +1066,13 @@ LLVMMetadataRef codegen_discope(compile_t* c)
 }
 
 void codegen_pushloop(compile_t* c, LLVMBasicBlockRef continue_target,
-  LLVMBasicBlockRef break_target)
+  LLVMBasicBlockRef break_target, LLVMBasicBlockRef break_novalue_target)
 {
   compile_frame_t* frame = push_frame(c);
 
   frame->fun = frame->prev->fun;
   frame->break_target = break_target;
+  frame->break_novalue_target = break_novalue_target;
   frame->continue_target = continue_target;
   frame->invoke_target = frame->prev->invoke_target;
   frame->di_file = frame->prev->di_file;
@@ -1088,6 +1090,7 @@ void codegen_pushtry(compile_t* c, LLVMBasicBlockRef invoke_target)
 
   frame->fun = frame->prev->fun;
   frame->break_target = frame->prev->break_target;
+  frame->break_novalue_target = frame->prev->break_novalue_target;
   frame->continue_target = frame->prev->continue_target;
   frame->invoke_target = invoke_target;
   frame->di_file = frame->prev->di_file;

src/libponyc/codegen/codegen.h

@@ -69,6 +69,7 @@ typedef struct compile_frame_t
   LLVMValueRef ctx;
 
   LLVMBasicBlockRef break_target;
+  LLVMBasicBlockRef break_novalue_target;
   LLVMBasicBlockRef continue_target;
   LLVMBasicBlockRef invoke_target;
 
@@ -218,7 +219,7 @@ LLVMMetadataRef codegen_difile(compile_t* c);
 LLVMMetadataRef codegen_discope(compile_t* c);
 
 void codegen_pushloop(compile_t* c, LLVMBasicBlockRef continue_target,
-  LLVMBasicBlockRef break_target);
+  LLVMBasicBlockRef break_target, LLVMBasicBlockRef break_novalue_target);
 
 void codegen_poploop(compile_t* c);
 

src/libponyc/codegen/gencontrol.c

@@ -182,7 +182,7 @@ LLVMValueRef gen_while(compile_t* c, ast_t* ast)
   }
 
   // Push the loop status.
-  codegen_pushloop(c, init_block, post_block);
+  codegen_pushloop(c, init_block, post_block, else_block);
 
   // init
   // This jumps either to the body or the else clause. This is not evaluated
@@ -300,7 +300,7 @@ LLVMValueRef gen_repeat(compile_t* c, ast_t* ast)
   }
 
   // Push the loop status.
-  codegen_pushloop(c, cond_block, post_block);
+  codegen_pushloop(c, cond_block, post_block, else_block);
 
   // Body.
   LLVMPositionBuilderAtEnd(c->builder, body_block);
@@ -383,33 +383,41 @@ LLVMValueRef gen_repeat(compile_t* c, ast_t* ast)
 LLVMValueRef gen_break(compile_t* c, ast_t* ast)
 {
   ast_t* body = ast_child(ast);
-  ast_t* body_type = ast_type(body);
 
-  // Get the break target.
-  LLVMBasicBlockRef target = c->frame->break_target;
+  LLVMBasicBlockRef target;
 
-  // Get the phi node.
-  LLVMValueRef post_phi = LLVMGetFirstInstruction(target);
-  bool needed = (post_phi != NULL) && LLVMIsAPHINode(post_phi);
+  if(ast_id(body) == TK_NONE)
+  {
+    target = c->frame->break_novalue_target;
+  } else {
+    ast_t* body_type = ast_type(body);
 
-  // Build the break expression.
-  LLVMValueRef value = gen_expr(c, body);
+    // Get the break target.
+    target = c->frame->break_target;
 
-  if(needed)
-  {
-    // Cast it to the phi type if we need to.
-    LLVMTypeRef phi_type = LLVMTypeOf(post_phi);
-    value = gen_assign_cast(c, phi_type, value, body_type);
-  }
+    // Get the phi node.
+    LLVMValueRef post_phi = LLVMGetFirstInstruction(target);
+    bool needed = (post_phi != NULL) && LLVMIsAPHINode(post_phi);
 
-  if(value == NULL)
-    return NULL;
+    // Build the break expression.
+    LLVMValueRef value = gen_expr(c, body);
 
-  // Add break value to the post block phi node.
-  if(needed)
-  {
-    LLVMBasicBlockRef insert_block = LLVMGetInsertBlock(c->builder);
-    LLVMAddIncoming(post_phi, &value, &insert_block, 1);
+    if(needed)
+    {
+      // Cast it to the phi type if we need to.
+      LLVMTypeRef phi_type = LLVMTypeOf(post_phi);
+      value = gen_assign_cast(c, phi_type, value, body_type);
+    }
+
+    if(value == NULL)
+      return NULL;
+
+    // Add break value to the post block phi node.
+    if(needed)
+    {
+      LLVMBasicBlockRef insert_block = LLVMGetInsertBlock(c->builder);
+      LLVMAddIncoming(post_phi, &value, &insert_block, 1);
+    }
   }
 
   // Jump to the break target.

src/libponyc/expr/control.c

@@ -393,17 +393,22 @@ bool expr_break(pass_opt_t* opt, ast_t* ast)
   // Add type to loop.
   ast_t* body = ast_child(ast);
 
-  if(is_control_type(ast_type(body)))
+  if(ast_id(body) != TK_NONE)
   {
-    ast_error(opt->check.errors, body,
-      "break value cannot be a control statement");
-    return false;
-  }
+    if(is_control_type(ast_type(body)))
+    {
+      ast_error(opt->check.errors, body,
+        "break value cannot be a control statement");
+      return false;
+    }
 
-  ast_t* loop_type = ast_type(t->frame->loop);
+    ast_t* loop_type = ast_type(t->frame->loop);
 
-  loop_type = control_type_add_branch(opt, loop_type, body);
-  ast_settype(t->frame->loop, loop_type);
+    // If there is no body the break will jump to the else branch, whose type
+    // has already been added to the loop type.
+    loop_type = control_type_add_branch(opt, loop_type, body);
+    ast_settype(t->frame->loop, loop_type);
+  }
 
   return true;
 }

src/libponyc/pass/sugar.c

@@ -496,7 +496,7 @@ static ast_result_t sugar_for(pass_opt_t* opt, ast_t** astp)
           NONE
           NODE(TK_DOT, NODE(TK_REFERENCE, ID(iter_name)) ID("next"))))
       NODE(TK_SEQ, AST_SCOPE
-        NODE(TK_CONTINUE, NONE))
+        NODE(TK_BREAK, NONE))
       NONE));
 
   sugar_try(try_next);
@@ -1413,8 +1413,7 @@ ast_result_t pass_sugar(ast_t** astp, pass_opt_t* options)
     case TK_NEW:        return sugar_new(options, ast);
     case TK_BE:         return sugar_be(options, ast);
     case TK_FUN:        return sugar_fun(options, ast);
-    case TK_RETURN:
-    case TK_BREAK:      return sugar_return(options, ast);
+    case TK_RETURN:     return sugar_return(options, ast);
     case TK_IF:
     case TK_MATCH:
     case TK_WHILE:

test/libponyc/sugar.cc

@@ -602,7 +602,7 @@ TEST_F(SugarTest, ForWithoutElse)
     "      let i = $try_no_check\n"
     "        $1.next()\n"
     "      else\n"
-    "        continue\n"
+    "        break\n"
     "      then\n"
     "        None\n"
     "      end\n"
@@ -633,7 +633,7 @@ TEST_F(SugarTest, ForWithElse)
     "      let i = $try_no_check\n"
     "        $1.next()\n"
     "      else\n"
-    "        continue\n"
+    "        break\n"
     "      then\n"
     "        None\n"
     "      end\n"
@@ -664,7 +664,7 @@ TEST_F(SugarTest, MultiIteratorFor)
     "      (let i, let j) = $try_no_check\n"
     "        $1.next()\n"
     "      else\n"
-    "        continue\n"
+    "        break\n"
     "      then\n"
     "        None\n"
     "      end\n"