compiler: explicitly represent loops in IR.

artiq/compiler/analyses/devirtualization.py

@@ -46,7 +46,7 @@ class FunctionResolver(algorithm.Visitor):
         self.visit(node.value)
         self.visit_in_assign(node.targets)
 
-    def visit_For(self, node):
+    def visit_ForT(self, node):
         self.visit(node.iter)
         self.visit_in_assign(node.target)
         self.visit(node.body)

artiq/compiler/asttyped.py

@@ -36,6 +36,12 @@ class ExceptHandlerT(ast.ExceptHandler):
     _fields = ("filter", "name", "body") # rename ast.ExceptHandler.type to filter
     _types = ("name_type",)
 
+class ForT(ast.For):
+    """
+    :ivar trip_count: (:class:`iodelay.Expr`)
+    :ivar trip_interval: (:class:`iodelay.Expr`)
+    """
+
 class SliceT(ast.Slice, commontyped):
     pass
 

artiq/compiler/ir.py

@@ -1296,7 +1296,7 @@ class Delay(Terminator):
 
     :ivar interval: (:class:`iodelay.Expr`) expression
     :ivar var_names: (list of string)
-        iodelay variable names corresponding to operands
+        iodelay variable names corresponding to SSA values
     """
 
     """
@@ -1354,6 +1354,68 @@ class Delay(Terminator):
     def opcode(self):
         return "delay({})".format(self.interval)
 
+class Loop(Terminator):
+    """
+    A terminator for loop headers that carries metadata useful
+    for unrolling. It includes an :class:`iodelay.Expr` specifying
+    the trip count, tied to SSA values so that inlining could lead
+    to the expression folding to a constant.
+
+    :ivar trip_count: (:class:`iodelay.Expr`)
+        expression for trip count
+    :ivar var_names: (list of string)
+        iodelay variable names corresponding to ``trip_count`` operands
+    """
+
+    """
+    :param trip_count: (:class:`iodelay.Expr`) expression
+    :param substs: (dict of str to :class:`Value`)
+        SSA values corresponding to iodelay variable names
+    :param cond: (:class:`Value`) branch condition
+    :param if_true: (:class:`BasicBlock`) branch target if condition is truthful
+    :param if_false: (:class:`BasicBlock`) branch target if condition is falseful
+    """
+    def __init__(self, trip_count, substs, cond, if_true, if_false, name=""):
+        for var_name in substs: assert isinstance(var_name, str)
+        assert isinstance(cond, Value)
+        assert builtins.is_bool(cond.type)
+        assert isinstance(if_true, BasicBlock)
+        assert isinstance(if_false, BasicBlock)
+        super().__init__([cond, if_true, if_false, *substs.values()], builtins.TNone(), name)
+        self.trip_count = trip_count
+        self.var_names = list(substs.keys())
+
+    def copy(self, mapper):
+        self_copy = super().copy(mapper)
+        self_copy.trip_count = self.trip_count
+        self_copy.var_names = list(self.var_names)
+        return self_copy
+
+    def condition(self):
+        return self.operands[0]
+
+    def if_true(self):
+        return self.operands[1]
+
+    def if_false(self):
+        return self.operands[2]
+
+    def substs(self):
+        return {key: value for key, value in zip(self.var_names, self.operands[3:])}
+
+    def _operands_as_string(self, type_printer):
+        substs = self.substs()
+        substs_as_strings = []
+        for var_name in substs:
+            substs_as_strings.append("{} = {}".format(var_name, substs[var_name]))
+        result = "[{}]".format(", ".join(substs_as_strings))
+        result += ", {}, {}, {}".format(*list(map(lambda value: value.as_operand(type_printer),
+                                                  self.operands[0:3])))
+        return result
+
+    def opcode(self):
+        return "loop({} times)".format(self.trip_count)
+
 class Parallel(Terminator):
     """
     An instruction that schedules several threads of execution

artiq/compiler/testbench/inferencer.py

@@ -2,6 +2,7 @@ import sys, fileinput, os
 from pythonparser import source, diagnostic, algorithm, parse_buffer
 from .. import prelude, types
 from ..transforms import ASTTypedRewriter, Inferencer, IntMonomorphizer
+from ..transforms import IODelayEstimator
 
 class Printer(algorithm.Visitor):
     """
@@ -34,6 +35,14 @@ class Printer(algorithm.Visitor):
             self.rewriter.insert_after(node.name_loc,
                                        ":{}".format(self.type_printer.name(node.name_type)))
 
+    def visit_ForT(self, node):
+        super().generic_visit(node)
+
+        if node.trip_count is not None and node.trip_interval is not None:
+            self.rewriter.insert_after(node.keyword_loc,
+                                       "[{} x {} mu]".format(node.trip_count.fold(),
+                                                             node.trip_interval.fold()))
+
     def generic_visit(self, node):
         super().generic_visit(node)
 
@@ -48,6 +57,12 @@ def main():
     else:
         monomorphize = False
 
+    if len(sys.argv) > 1 and sys.argv[1] == "+iodelay":
+        del sys.argv[1]
+        iodelay = True
+    else:
+        iodelay = False
+
     if len(sys.argv) > 1 and sys.argv[1] == "+diag":
         del sys.argv[1]
         def process_diagnostic(diag):
@@ -71,6 +86,8 @@ def main():
     if monomorphize:
         IntMonomorphizer(engine=engine).visit(typed)
         Inferencer(engine=engine).visit(typed)
+    if iodelay:
+        IODelayEstimator(engine=engine, ref_period=1e6).visit_fixpoint(typed)
 
     printer = Printer(buf)
     printer.visit(typed)

artiq/compiler/transforms/artiq_ir_generator.py

@@ -472,7 +472,7 @@ class ARTIQIRGenerator(algorithm.Visitor):
         else:
             assert False
 
-    def visit_For(self, node):
+    def visit_ForT(self, node):
         try:
             iterable = self.visit(node.iter)
             length = self.iterable_len(iterable)
@@ -522,6 +522,11 @@ class ARTIQIRGenerator(algorithm.Visitor):
             else:
                 else_tail = tail
 
+            if node.trip_count is not None:
+                substs = {var_name: self.current_args[var_name]
+                          for var_name in node.trip_count.free_vars()}
+                head.append(ir.Loop(node.trip_count, substs, cond, body, else_tail))
+            else:
                 head.append(ir.BranchIf(cond, body, else_tail))
             if not post_body.is_terminated():
                 post_body.append(ir.Branch(continue_block))

artiq/compiler/transforms/asttyped_rewriter.py

@@ -471,6 +471,15 @@ class ASTTypedRewriter(algorithm.Transformer):
             self.engine.process(diag)
         return node
 
+    def visit_For(self, node):
+        node = self.generic_visit(node)
+        node = asttyped.ForT(
+            target=node.target, iter=node.iter, body=node.body, orelse=node.orelse,
+            trip_count=None, trip_interval=None,
+            keyword_loc=node.keyword_loc, in_loc=node.in_loc, for_colon_loc=node.for_colon_loc,
+            else_loc=node.else_loc, else_colon_loc=node.else_colon_loc)
+        return node
+
     # Unsupported visitors
     #
     def visit_unsupported(self, node):

artiq/compiler/transforms/inferencer.py

@@ -916,7 +916,7 @@ class Inferencer(algorithm.Visitor):
 
             node.value = self._coerce_one(value_type, node.value, other_node=node.target)
 
-    def visit_For(self, node):
+    def visit_ForT(self, node):
         old_in_loop, self.in_loop = self.in_loop, True
         self.generic_visit(node)
         self.in_loop = old_in_loop

artiq/compiler/transforms/iodelay_estimator.py

@@ -167,7 +167,7 @@ class IODelayEstimator(algorithm.Visitor):
                 node.loc)
             abort([note])
 
-    def visit_For(self, node):
+    def visit_ForT(self, node):
         self.visit(node.iter)
 
         old_goto, self.current_goto = self.current_goto, None
@@ -180,8 +180,9 @@ class IODelayEstimator(algorithm.Visitor):
                 self.abort("loop trip count is indeterminate because of control flow",
                            self.current_goto.loc)
 
-            trip_count = self.get_iterable_length(node.iter)
-            self.current_delay = old_delay + self.current_delay * trip_count
+            node.trip_count    = self.get_iterable_length(node.iter).fold()
+            node.trip_interval = self.current_delay.fold()
+            self.current_delay = old_delay + node.trip_interval * node.trip_count
         self.current_goto = old_goto
 
         self.visit(node.orelse)