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Branch Scenario Verification

Concept

Branch Scenario Verification is a constrained-random microprocessor verification approach for generating useful forward and backward branch instruction scenarios. It raises the chance that forward branches exercise taken/not-taken logic and constrains backward branches as bounded loop scenarios to avoid excessively long or endless execution.

First seen 5/28/2026
Last seen 5/28/2026
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Overview

Branch Scenario Verification addresses a common weakness of automatic microprocessor instruction generation: unconstrained random register values rarely create useful branch behavior. For example, random 32-bit register contents make equality comparisons such as BEQ R1, R2 unlikely to be true, so forward branches tend to fall through and may miss branch-condition evaluation logic. Likewise, a backward branch such as BNE R3, R4 can keep execution in a loop for a very long time when the compared registers almost never become equal. [C1]

The technique uses constrained scenarios to restrict relationships among nearby instructions and operands. These constraints make branch outcomes more controllable while preserving randomness in the generated instruction stream. [C2]

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RELATIONSHIPS

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Forward Branch Probability Enhancement uses → 95% 1e
Branch scenario verification uses forward branch probability enhancement to increase taken-branch likelihood.
Backward Branch Loop Control uses → 95% 1e
Branch scenario verification uses backward branch loop control to prevent infinite loops.
Constraint-Based Randomization uses → 93% 1e
Constrained scenarios are used to handle branch verification challenges.

LINKED ENTITIES

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Forward Branch Probability Enhancement USES Extracted graph relationship
Backward Branch Loop Control USES Extracted graph relationship
Constraint-Based Randomization USES Extracted graph relationship

CITATIONS

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9 citations — click to expand
[1] Random register values make equality-based forward branches unlikely to be taken and can cause backward branch loops to run for a very long time. Applying constrained-random verification to microprocessors
[2] Constrained scenarios can restrict sequences of operations so that forward branch probability becomes reasonable and endless backward-branch loops are avoided. Applying constrained-random verification to microprocessors
[3] Initializing branch comparison operands with an ADDI such as R1 = R2 + {-2:2} can make equality occur with 20% probability in the cited example. Applying constrained-random verification to microprocessors
[4] A forward branch can be constrained so that the immediately preceding operation is an ADDI with the same operands and a small immediate value. Applying constrained-random verification to microprocessors
[5] Backward branches can be treated as loop scenarios in which register values are brought closer each iteration until the branch falls through. Applying constrained-random verification to microprocessors
[6] Backward-branch constraints include using a preceding ADDI with the same operands and a small negative value, incrementing the loop index inside the loop just before the branch, and preventing other loop instructions from modifying the branch operands. Applying constrained-random verification to microprocessors
[7] Boundary conditions must be considered because a backward branch such as BGT R1, R2, LABEL_X can be always taken if R2 has the smallest possible value. Applying constrained-random verification to microprocessors
[8] Pure random instruction sequences are often not useful for processor verification, and instruction-scenario base classes can encode constraints such as memory-alignment rules that may be disabled to generate exception cases. Applying constrained-random verification to microprocessors
[9] Processor stimulus generation can use constrained-random scenarios, directed-random scenarios, and directed scenarios loaded from pre-assembled program traces. Applying constrained-random verification to microprocessors