Single-Path Code Generation and Input-Data Dependence Analysis

Transcription

1 Single-Path Code Generation and Input-Data Dependence Analysis Daniel Prokesch July 10 th, 2014 Project Workshop Madrid D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

2 Motivation Uncertainty in program execution time D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

3 Motivation Uncertainty in program execution time Hardware Duration of operations dependent on internal state D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

4 Motivation Uncertainty in program execution time Hardware Duration of operations dependent on internal state Software Different inputs lead to paths of varying execution time D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

5 The Single-Path Approach Singleton execution path Reduce complexity of path analysis D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

6 The Single-Path Approach Singleton execution path Reduce complexity of path analysis Execution time stable w.r.t. varying input data Known ET for a particular input Reasonable predictions for any input D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

7 The Single-Path Approach Eliminate input-data dependent control flow. D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

8 The Single-Path Approach Eliminate input-data dependent control flow. Predicated execution (guard) instruction; If-conversion if (cond) { x = a + 1; } else { x = b - 2; } ( cond) x = a + 1; (!cond) x = b - 2; D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

9 Single-Path Transformation Rules Rules to transform from high-level language to single-path sequence of predicated statements [Puschner et al., 2012] D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

10 Single-Path Transformation Rules Rules to transform from high-level language to single-path sequence of predicated statements [Puschner et al., 2012] Example: Treatment of loops while (cond) // max N times { stmts; } finished := false; for i = 1.. N { if (!cond) finished := true; if (!finished) { stmts; } } D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

11 Single-Path Transformation Rules Rules to transform from high-level language to single-path sequence of predicated statements [Puschner et al., 2012] Example: Treatment of loops while (cond) // max N times { stmts; } finished := false; for i = 1.. N { if (!cond) finished := true; if (!finished) { stmts; } } How to implement this in a compiler?? D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

12 Single-Path Code Generation Contributions Formulation of the single-path transformation on the CFG level D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

13 Single-Path Code Generation Contributions Formulation of the single-path transformation on the CFG level Prototype implementation in a code generator (LLVM backend for Patmos) D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

14 Control-flow Graph Nodes with at most two successors Branch condition Reducible control flow graph D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

15 The Single-Path Graph Transformation Admissible paths in CFG: local loop bounds Predicated Nodes Semantic actions on predicates at nodes and edges D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

16 The Single-Path Graph Transformation Admissible paths in CFG: local loop bounds Predicated Nodes Semantic actions on predicates at nodes and edges D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

17 Acyclic regions [Park and Schlansker, 1991] describe transformation in acyclic case s a Partitioning by Control Dependence b c d e t D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

18 Acyclic regions [Park and Schlansker, 1991] describe transformation in acyclic case s a b c Partitioning by Control Dependence Nodes with same set of CD: same predicate d e t D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

19 Acyclic regions [Park and Schlansker, 1991] describe transformation in acyclic case s a b c Partitioning by Control Dependence Nodes with same set of CD: same predicate d e t D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

20 Acyclic regions [Park and Schlansker, 1991] describe transformation in acyclic case s t a b d e c Partitioning by Control Dependence Nodes with same set of CD: same predicate Predicate assignments at source of CD edges Initialization with false Topological sort order D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

21 Loops Forward control flow graph of loop nodes Nested inner loops compacted into single node Proceed as in acyclic case D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

22 Loops Forward control flow graph of loop nodes Nested inner loops compacted into single node Proceed as in acyclic case Input-data independent branch condition Former exit edge causes clearing of header predicate D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

23 Loops Forward control flow graph of loop nodes Nested inner loops compacted into single node Proceed as in acyclic case Input-data independent branch condition Former exit edge causes clearing of header predicate Recursive composition of the SP-Graph starting from outermost (pseudo-) loop D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

24 Input-Data Dependency Analysis 1 Determine input-data dependent branch conditions 1 work mostly by Benedikt Huber D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

25 Input-Data Dependency Analysis 1 Determine input-data dependent branch conditions Input data dependency Definition based on Thinned Gated Static Assignment (TGSA) form 1 work mostly by Benedikt Huber D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

26 Input-Data Dependency Analysis 1 Determine input-data dependent branch conditions Input data dependency Definition based on Thinned Gated Static Assignment (TGSA) form γ-instructions, µ-instructions, η-instructions capture various types of dependencies 1 work mostly by Benedikt Huber D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

27 Input-Data Dependency Analysis 1 Determine input-data dependent branch conditions Input data dependency Definition based on Thinned Gated Static Assignment (TGSA) form γ-instructions, µ-instructions, η-instructions capture various types of dependencies From TGSA, input-data dependency graph is constructed Path from x y: x may depend on y, otherwise x is independent from y 1 work mostly by Benedikt Huber D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

28 Implementation Prototype implementation in Patmos backend (LLVM) D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

29 Implementation Prototype implementation in Patmos backend (LLVM) Patmos features... A fully predicated instruction set 7+1 predicate registers that can be stored/restored at once Explicitly managed local memories D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

30 Example: Insertion Sort Fetch array to SPM, sort, copy back to memory Exhaustive simulation D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

31 Example: Insertion Sort Fetch array to SPM, sort, copy back to memory Exhaustive simulation Results: Static Analysis 771 D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

32 Example: Insertion Sort Fetch array to SPM, sort, copy back to memory Exhaustive simulation Results: Static Analysis 771 Static Analysis w/ LC 546 D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

33 Example: Insertion Sort Fetch array to SPM, sort, copy back to memory Exhaustive simulation Results: Static Analysis 771 Static Analysis w/ LC 546 Measurements [473, 501] D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

34 Example: Insertion Sort Fetch array to SPM, sort, copy back to memory Exhaustive simulation Results: Static Analysis 771 Static Analysis w/ LC 546 Measurements [473, 501] Single-Path (single-issue) 580 D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

35 Example: Insertion Sort Fetch array to SPM, sort, copy back to memory Exhaustive simulation Results: Static Analysis 771 Static Analysis w/ LC 546 Measurements [473, 501] Single-Path (single-issue) 580 Single-Path 485 D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

36 Summary Single-path conversion as transformation on CFGs Prototype implementation in Patmos backend D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,

37 References I Park, J. C. and Schlansker, M. (1991). On predicated execution. Technical report, Hewlett Peckard Software and Systems Laboratory. Puschner, P., Kirner, R., Huber, B., and Prokesch, D. (2012). Compiling for time predictability. In Proc. SAFECOMP 2012 Workshops (LNCS 7613), pages Springer. D. Prokesch TUV T-CREST Workshop, Madrid July 10 th,