LLVM Essentials

Emitting if-else condition IR

An if-else statement has a condition expression and two code paths to execute, depending on the condition evaluating to true or false. The condition expression is generally a comparison statement. Let's emit a condition statement at the start of the block. For example, let the condition be like a<100.

 Value *val2 = Builder.getInt32(100);
 Value *Compare = Builder.CreateICmpULT(val, val2, "cmptmp"); 

On compilation, we get following output:

; ModuleID = 'my compiler'

@x = common global i32, align 4

define i32 @foo(i32 %a, i32 %b) {
entry:
  %multmp = mul i32 %a, 16
  %cmptmp = icmp ult i32 %multmp, 100
  
  ret i32 %multmp
}

The next step is to define the then and else block expressions, which will be executed depending on the ...