Make the block iterator an AbstractVector too.

Author: maleadt

src/core/function.jl

@@ -115,24 +115,39 @@ end
 
 export blocks
 
-struct FunctionBlockSet
+struct FunctionBlockSet <: AbstractVector{BasicBlock}
     f::Function
+    cache::Vector{API.LLVMValueRef}
+
+    FunctionBlockSet(f::Function) = new(f, BasicBlock[])
 end
 
 blocks(f::Function) = FunctionBlockSet(f)
 
-Base.eltype(::FunctionBlockSet) = BasicBlock
-
-function Base.iterate(iter::FunctionBlockSet, state=API.LLVMGetFirstBasicBlock(iter.f))
-    state == C_NULL ? nothing : (BasicBlock(state), API.LLVMGetNextBasicBlock(state))
-end
+Base.size(iter::FunctionBlockSet) = (Int(API.LLVMCountBasicBlocks(iter.f)),)
 
 Base.first(iter::FunctionBlockSet) = BasicBlock(API.LLVMGetFirstBasicBlock(iter.f))
 Base.last(iter::FunctionBlockSet) = BasicBlock(API.LLVMGetLastBasicBlock(iter.f))
 
-Base.isempty(iter::FunctionBlockSet) = length(iter) == 0
+function Base.iterate(iter::FunctionBlockSet, state=API.LLVMGetFirstBasicBlock(iter.f))
+    state == C_NULL ? nothing : (BasicBlock(state), API.LLVMGetNextBasicBlock(state))
+end
 
-Base.length(iter::FunctionBlockSet) = API.LLVMCountBasicBlocks(iter.f)
+# provide a random access interface by maintaining a cache of blocks
+function Base.getindex(iter::FunctionBlockSet, i::Int)
+    i <= 0 && throw(BoundsError(iter, i))
+    i == 1 && return first(iter)
+    while i > length(iter.cache)
+        next = if isempty(iter.cache)
+            iterate(iter)
+        else
+            iterate(iter, iter.cache[end])
+        end
+        next === nothing && throw(BoundsError(iter, i))
+        push!(iter.cache, next[2])
+    end
+    return BasicBlock(iter.cache[i-1])
+end
 
 # NOTE: optimized `collect`
 function Base.collect(iter::FunctionBlockSet)