Ternary Expressions, Improved Integer Divisions, and Iteration Space Fix

Ternary expressions

This MR introduces ast nodes, typification, constant folding, and printing of ternary a ? b : c expressions. On top of that, freezing support for sympy.Piecewise is introduced.

Integer Division Improvements

This MR introduces the PsRem expression node for the C % operator, and adds constant folding for C-style integer division and remainder operations.

Fix: Iteration Space work items

Using the above, this MR fixes the computation of the amount of work items in an interation space if start, stop and step don't align.

src/pystencils/backend/transformations/eliminate_constants.py

@@ -27,6 +27,7 @@ from ..ast.expressions import (
     PsLt,
     PsGt,
     PsNe,
+    PsTernary,
 )
 from ..ast.util import AstEqWrapper
 
@@ -247,6 +248,13 @@ class EliminateConstants:
                 false = self._typify(PsConstantExpr(PsConstant(False, PsBoolType())))
                 return false, True
 
+            #   Trivial ternaries
+            case PsTernary(PsConstantExpr(c), then, els):
+                if c.value:
+                    return then, subtree_constness[1]
+                else:
+                    return els, subtree_constness[2]
+
         # end match: no idempotence or dominance encountered
 
         #   Detect constant expressions