Basic blocks

Basic blocks are sequences of instructions that are executed in order. They are the building blocks of functions, and can be looked up using the blocks iterator, or by constructing them directly:

julia> bb = BasicBlock("SomeBlock")
SomeBlock:                                        ; No predecessors!

A detached basic block often not what you want; using the BasicBlock(::Function) constructor you can instead append to a function, or insert before another block using the BasicBlock(::BasicBlock) constructor.

Basic blocks support a couple of specific APIs:

• name: the name of the basic block.
• parent: the parent function of the basic block, or nothing if it is detached.
• terminator: get the terminator instruction of the block.
• move_before/move_after: move the block before or after another block.
• remove!/erase!: delete the basic block from its parent function, or additionally also delete the block itself.

Control flow

The LLVM C API supports a couple of functions to inspect the control flow of basic blocks:

• predecessors: get the predecessors of a basic block.
• successors: get the successors of a basic block.

Instructions

The main purpose of basic blocks is to contain instructions, which can be iterated using the instructions function:

julia> bb
top:
  %2 = add i64 %1, %0
  ret i64 %2

julia> collect(instructions(bb))
2-element Vector{Instruction}:
 %2 = add i64 %1, %0
 ret i64 %2

In addition to the iteration interface, it is possible to move from one instruction to the previous or next one using respectively the previnst and nextinst functions.