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by tssva 1646 days ago
I'm not a programmer by profession and barely one by hobby. I know nothing about compiler internals but looking at the definition of a basic block from Wikipedia, "In compiler construction, a basic block is a straight-line code sequence with no branches in except to the entry and no branches out except at the exit." it seems that the ternary operators in "return (x ? a : b) + (y ? c : d);" although part of the same programming block would be distinct compiler basic blocks.
2 comments
comex 1645 days ago
Indeed, it seems contradictory to be talking about converting multiple branches within a basic block. Or even a single branch, for that matter.

Perhaps they're talking about what ends up in a single basic block after the conversion to cmov? Still an odd way to describe it.

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dragontamer 1646 days ago
Basic blocks are how compilers "conceptualize" our code and start thinking about optimization.

Frankly, my recommendation to you is to ignore that stuff. You need like 3 or 4 years of school to reach that level. You should have studied easier graph optimization problems (ex: Finite Automatia) first, before dealing with code-optimization.

The school curriculum is typically Programming 101 -> Data Structures -> Algorithms -> Finite Automata (aka: Regex) -> Pushdown Automata (aka: context-free grammars) -> Turing Machines (aka: general purpose code) -> Compilers (which use Finite Automata, Pushdown Automata, and Turing Machines simultaneously).

Basic Blocks are the graph structure that compilers use to think about code. Its a lot of graph-theory built up on a lot of language theory.

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That being said: if you're actually interested in this stuff, then feel free to explore. But just beware, you've stumbled upon a very complex subject that is easily 4th year undergrad or even graduate-school level.

With enough effort, you'll understand things. But this is no subject for beginners to go around exploring by themselves.

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That being said, I want to encourage you to explore the subject anyway. Just explore the subject with awareness that there's a lot to understand here.

If you want to skip the 3ish years of elementary data-structures / comp. sci theory... I suggest starting with Static Single Assignment and working forward from here.

https://en.wikipedia.org/wiki/Static_single_assignment_form

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