Abstract Syntax Tree

Canonical Form

Many transformations in pystencils’ backend require that their input AST is in canonical form. This means that:

• Each symbol, constant, and expression node is annotated with a data type;

• Each symbol has at most one declaration;

• Each symbol that is never written to apart from its declaration has a const type; and

• Each symbol whose type is not const has at least one non-declaring assignment.

The first requirement can be ensured by running the Typifier on each newly constructed subtree. The other three requirements are ensured by the CanonicalizeSymbols pass, which should be run first before applying any optimizing transformations.

Canonicality allows transformations to forego various checks that would otherwise be necessary to prove their legality.

API Documentation

Inheritance Diagram

Base Classes

PsAstNode	Base class for all nodes in the pystencils AST.
PsAstNodeChildrenMixin	Mix in with PsAstNode to use default implementations of get_children and set_child.
PsLeafMixIn	Mix-in for AST leaves.

Structural Nodes

PsBlock
PsStatement
PsAssignment
PsDeclaration
PsLoop
PsConditional	Conditional branch
PsEmptyLeafMixIn	Mix-in marking AST leaves that can be treated as empty by the code generator, such as comments and preprocessor directives.
PsPragma	A C/C++ preprocessor pragma.
PsComment

Iteration Axes System

PsAxisRange	Iteration range of an axis.
PsAxesCube	Hypercube of multiple iteration ranges.
PsIterationAxis	Common base class for iteration axes.
PsLoopAxis	Loop axis.
PsParallelLoopAxis	Parallel loop axis.
PsSimdAxis	Axis modelling a SIMD block.
PsGpuIndexingAxis	Common base class for GPU block+thread indexing axes.
PsGpuBlockAxis	Gpu block axis.
PsGpuThreadAxis	Gpu thread axis.
PsGpuBlockXThreadAxis	Gpu block x thread axis.

Expressions

PsExpression	Base class for all expressions.
PsLvalue	Mix-in for all expressions that may occur as an lvalue; i.e. expressions that represent a memory location.
PsSymbolExpr	A single symbol as an expression.
PsConstantExpr
PsLiteralExpr
PsBufferAcc	Access into a PsBuffer.
PsSubscript	N-dimensional subscript into an array.
PsMemAcc	Pointer-based memory access with type-dependent offset.
PsLookup
PsCall
PsTernary	Ternary operator.
PsNumericOpTrait	Trait for operations valid only on numerical types
PsIntOpTrait	Trait for operations valid only on integer types
PsBoolOpTrait	Trait for boolean operations
PsUnOp
PsNeg
PsAddressOf	Take the address of a memory location.
PsCast	C-style type cast.
PsBinOp
PsAdd
PsSub
PsMul
PsDiv
PsIntDiv	C-like integer division (round to zero).
PsRem	C-style integer division remainder
PsLeftShift
PsRightShift
PsBitwiseAnd
PsBitwiseXor
PsBitwiseOr
PsAnd
PsOr
PsNot
PsRel	Base class for binary relational operators
PsEq
PsNe
PsGe
PsLe
PsGt
PsLt
PsArrayInitList	N-dimensional array initialization matrix.

SIMD Nodes

PsVectorOp	Mix-in for vector operations
PsVecBroadcast	Broadcast a scalar value to N vector lanes.
PsVecMemAcc	Pointer-based vectorized memory access.

Utility

expressions.evaluate_expression	Evaluate a pystencils backend expression tree with values assigned to symbols according to the given valuation.
dfs_preorder	Pre-Order depth-first traversal of an abstract syntax tree.
dfs_postorder	Post-Order depth-first traversal of an abstract syntax tree.
util.determine_memory_object	Return the memory object accessed by the given expression, together with its constness