Support continue within foreach (on sequences)

Author: lwaern-intel

RELEASENOTES-1.4.md

@@ -330,3 +330,5 @@
   signatures of unused `shared` methods were not properly checked, leading to
   invalid generated C.
 - `release 6 6329`
+- `note 6` `continue` can now be used within `foreach` loops (use within
+  `#foreach` loops remains unsupported)

doc/1.4/language.md

@@ -3784,7 +3784,8 @@ within the body.
 DML currently only supports `foreach` iteration on values of `sequence` types
 — which are created through [Each-In expressions](#each-in-expressions).
 
-The `break` statement can be used within a `foreach` loop to exit it.
+The `continue` statement can be used within a `foreach` loop to continue to the
+next element, and the `break` statement can be used to exit the loop.
 
 <pre>
 #foreach <em>identifier</em> in (<em>expr</em>) <em>statement</em>

py/dml/codegen.py

@@ -104,18 +104,26 @@ def __enter__(self):
     def __exit__(self, exc_type, exc_val, exc_tb):
         assert LoopContext.current is self
         LoopContext.current = self.prev
+    @abstractmethod
+    def break_(self, site): pass
+    def continue_(self, site):
+        raise ECONTU(site)
 
 class CLoopContext(LoopContext):
     '''DML loop context corresponding to a C loop'''
     def break_(self, site):
         return [mkBreak(site)]
+    def continue_(self, site):
+        return [mkContinue(site)]
 
 class NoLoopContext(LoopContext):
     '''DML loop context corresponding to an inlined method call.
     This is used to delimit the loop stack between the method containing
     the inline method call and the method called.'''
     def break_(self, site):
         raise EBREAK(site)
+    def continue_(self, site):
+        raise ECONT(site)
 
 class GotoLoopContext(LoopContext):
     '''DML loop context not directly corresponding to a single C loop
@@ -131,6 +139,13 @@ def break_(self, site):
         self.used = True
         return [mkGotoBreak(site, self.label)]
 
+class ForeachSequenceLoopContext(GotoLoopContext):
+    '''DML loop context corresponding to a foreach loop on an each-in sequence
+    Uses of `break` is codegen:d as a goto past the outer loop, and `continue`
+    is codegen:d as a `continue` of the inner loop'''
+    def continue_(self, site):
+        return [mkContinue(site)]
+
 class Failure(ABC):
     '''Handle exceptions failure handling is supposed to handle the various kind of
     functions that are generated, with different ways of signaling
@@ -3065,7 +3080,7 @@ def foreach_each_in(site, itername, trait, each_in,
     inner_scope.add_variable(
         itername, type=trait_type, site=site,
         init=ForeachSequence.itervar_initializer(site, trait))
-    context = GotoLoopContext()
+    context = ForeachSequenceLoopContext()
     with context:
         inner_body = mkCompound(site, declarations(inner_scope)
             + codegen_statements([body_ast], location, inner_scope))
@@ -3261,13 +3276,10 @@ def stmt_switch(stmt, location, scope):
 
 @statement_dispatcher
 def stmt_continue(stmt, location, scope):
-    if (LoopContext.current is None
-        or isinstance(LoopContext.current, NoLoopContext)):
+    if LoopContext.current is None:
         raise ECONT(stmt.site)
-    elif isinstance(LoopContext.current, CLoopContext):
-        return [mkContinue(stmt.site)]
     else:
-        raise ECONTU(stmt.site)
+        return LoopContext.current.continue_(stmt.site)
 
 @statement_dispatcher
 def stmt_break(stmt, location, scope):

py/dml/messages.py

@@ -956,8 +956,8 @@ class ECONT(DMLError):
 
 class ECONTU(DMLError):
     """
-    A `continue` statement cannot be used in a `foreach`
-    or `select` statement.
+    A `continue` statement cannot be used in a `#foreach`
+    or `#select` statement.
     """
     fmt = "continue is not possible here"
 

test/1.4/expressions/T_each_in.dml

@@ -31,6 +31,16 @@ group test is t2 {
     group sub is t2;
 }
 
+template t3 {}
+
+group g1 is t3;
+
+group g2[i < 2][j < 3] is t3;
+
+group p[i < 2][j < 3] {
+    group g3[k < 5] is t3;
+}
+
 method init() {
     local bool found = false;
     foreach obj in (each tr in (a.b[0].d)) {
@@ -75,4 +85,22 @@ method init() {
     assert test.name == dev.name;
     assert (each t2 in (test)).len == 1;
     assert (each t2 in (dev)).len == 1;
+
+    local uint32 count = 0;
+    foreach g in (each t3 in (dev)) {
+        // Meant to smoke-test that continue only skips one particular flat_index
+        // for one particular node
+        if (cast(g1, t3) == g
+            || cast(g2[0][0], t3) == g
+            || cast(g2[0][2], t3) == g
+            || cast(g2[1][2], t3) == g
+            || cast(p[1][1].g3[0], t3) == g
+            || cast(p[1][2].g3[2], t3) == g) {
+            continue;
+        }
+        ++count;
+    }
+
+    // total - skipped
+    assert count == 1 + 2*3 + 2*3*5 - 6;
 }