Examples of kilim.analysis.BasicBlock

• kilim.analysis.BasicBlock
  A basic block is a contiguous set of instructions that has one label at the first instruction and a transfer-of-control instruction at the very end. A transfer-of-control instruction includes all branching instructions that have labelled targets (IF_x, GOTO, and JSR) and the rest (ATHROW, xRETURN, RET). There can be no target labels in the middle of a basic block; in other words, you can't jump into the middle of a basic block. This is the standard definition; we make a few changes.

  We create BasicBlocks whenever we encounter a label (in a linear scanning of a method's instructions. Some labels are meant for catch handlers and debug (line number) information only; they are not the target of a branching instruction, but we don't know that in the first pass. We coalesce those BasicBlocks that merely follow another, provided the preceding BB is the only preceder. Note that blocks connected with a GOTO can't coalesce because they are not likely to be contiguous, even if they obey the constraint of a single edge. We also don't coalesce blocks starting with a pausable method invocation with their predecessor, because we need these blocks to tell us about downstream usage of local vars to help us generate optimal continuations.

  All catch handlers that intersect a basic block are treated as successors to the block, for the purposes of liveness analysis.

  Subroutines (targets of JSR) are treated specially. We inline all JSR calls, including nested JSRs, to simplify liveness analysis. In this phase, a JSR/RET is treated the same as a GOTO sub followed by a GOTO to the caller. During the weaving phase, we ignore the inlining information if the subroutine doesn't have any pausable methods. If it does, then we spit out duplicate code, complete with GOTOs as described above. This allows us to jump in the middle of a "finally" block during rewinding. Note: The JVM reference doesn't specify the boundaries of a JSR instruction; in other words, there is no definitive way of saying which blocks belong to a subroutine. This code treats the set of all nodes reachable via branching instructions from the subroutine's entry point. (exception catch blocks don't count)

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