Control-Flow Linearization Safety for Diamond CFG Load Paths
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Solution Overview
Problem
Existing compiler approaches face challenges in statically proving the safety of pointer dereferences in control-flow divergence, which inhibits effective control-flow linearization and subsequent optimizations like loop vectorization.
Innovation Solution
A computer-implemented process for static safety analysis that identifies memory load instructions in a diamond-shape structure within a control flow graph, determining if their addresses are used uniformly across all paths and if the immediate predecessor post-dominates the loop header, thereby affirming the safety of linearization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If control-flow linearization is applied to eliminate conditional branches, then compiler optimization capability is improved, but proof of safety for pointer dereferences becomes more difficult
Solution Approach 1:
The patent segments the control flow graph into diamond-shaped structures and processes each diamond independently. By dividing the linearization problem into discrete diamond units with specific entry and exit points, the compiler can analyze and transform each segment separately, making safety verification more manageable while enabling systematic optimization across the entire function.
Solution Approach 2:
The patent performs preliminary analysis to identify diamond-shaped control flow structures before applying linearization transformations. By pre-characterizing the control flow graph and marking diamonds that are safe to linearize based on pointer usage patterns, the compiler prepares the transformation in advance, reducing the complexity of safety proofs during the actual optimization phase.
2Reliability
If extensive dereferenceability proofs are required, then safety is improved, but transformation complexity increases
Solution Approach 1:
The patent applies different safety verification strategies to different regions of the control flow graph. Instead of requiring uniform extensive proofs throughout, it identifies specific diamond structures where pointer dereferences have consistent behavior across all paths, allowing localized safety assertions that reduce overall transformation complexity while maintaining reliability.
Solution Approach 2:
The patent copies pointer values and their associated safety information across diamond boundaries when the pointers are used uniformly on all paths. By copying the pointer state and validation information rather than re-proving dereferenceability at each boundary, the system maintains safety guarantees while reducing the complexity of repeated verification.
Data Source
AI summary
A static safety analysis for control-flow linearization receives a control flow graph (CFG) and an intermediate representation of a computer program, and identifies, for a given loop, all memory load instructions belonging to one side of a diamond-shape structure in the CFG. For each representation of an address of each memory load instruction identified, determining whether it is used on all other sides of the diamond-shape structure. Responsive to determining each representation of an address of each memory load instruction on the one side of the diamond-shape structure is used on all other sides of the diamond-shape structure, determining whether an immediate predecessor of a top of the diamond-shape structure for the given loop post-dominates a header of the given loop. Responsive to determining the immediate predecessor of the top of the diamond-shape structure for the given loop post-dominates the header of the given loop, affirming safety of linearization.