Build a Compiler from Scratch（IR Basic）

Posted on 2022-07-05 Edited on 2022-07-07 In Compiler Theory Waline: Symbols count in article: 929 Reading time ≈ 1 mins.

Study LLVM to build our kemomimi compiler

Simple Grammar of the LLVM IR

i32: 32-bits int

i1: 1-bit int

void: nothing, just take a place

label: label a block, help the machine to jump

Array: an Array

Function Definition: define i32 @main(i32 %a,i32 %b, \cdots) {}

Function Declaration: declare void @putarray(i32, i32*)

Wrapping a bunch of instructions and end with a terminator instruction, without any loop or brunch. Just move linearly.

Attention： A basic block could have a call instruction in it.

e.g. :ret br

ret:

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return 0

ret i32 0

br

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if (a = b) {} else {}

br i1 %9, label %10, label %11

The %9 should be set ahead with instructions like icmp . %10 and %11 are two labeled blocks.

Or just:

1	br label %10 when it finishes a block

The most important classes are Value, Use, and User.

BasicBlock, Argument, User are inherited from Value.

Constant and Instruction are inherited from User.

Function inherited from Constant by multiple inheritances, so Function is also Value and User.

The Structure