Value-Based Partial Redundancy Elimination

Abstract

Abstract. Partial redundancy elimination (PRE) is a program transformation that identifies and eliminates expressions that are redundant on at least one (but not necessarily all) execution paths. Global value numbering (GVN) is a program analysis and transformation that identifies operations that compute the same value and eliminates operations that are redundant. A weakness of PRE is that it traditionally considers only expressions that are lexically equivalent. A weakness of GVN is that it traditionally considers only operations that are fully redundant. In this paper, we examine the work that has been done on PRE and GVN and present a hybrid algorithm that combines the strengths of each. The contributions of this work are a framework for thinking about expressions and values without source-level lexical constraints, a system of data-flow equations for determining insertion points, and a practical algorithm for extending a simple hash-based GVN for PRE. Our implementation subsumes GVN statically and, on most benchmarks, in terms of performance.

Optimizing JIT-compilation subsystem for Rotor 2.0

“…The value numbering procedure is similar to the one described in [9], i.e., temporaries and expressions are grouped into values, and a "leader" temporary is choused, but upward lookup and partial redundancy elimination is not performed. Instead, the fast loop optimization algorithm built into the forward lookup pass accomplishes the same task.…”

DeAliaser

“…In this case, PRE makes those expressions fully redundant by performing code motion across the control flow graph [20]. LLVM utilizes a PRE algorithm based on static single assignment (SSA) form that performs GVN simultaneously [40].…”

An Improved Algorithm for Redundancy Detection Using Global Value Numbering

“…Briggs et al [11] give a comparison of the different techniques for value numbering with respect to their use in different kinds of optimizations. A recent work of VanDrunen and Hosking [12] is on the use of GVN for PRE. Most of the GVN algorithms [3,7,13,14] require the program to be represented in static single assignment (SSA) form [15].…”