Skip to content

Latest commit

 

History

History
34 lines (27 loc) · 804 Bytes

Loops.md

File metadata and controls

34 lines (27 loc) · 804 Bytes

Loops in LLVM IR

In LLVM IR you can make loops by playing with labels, using the br instruction with comparisons either to integers icmp or floats or doubles like fcmp.

An example with a counter:

%0 = alloca i64, align 4 ; Allocate the counter
store i64 0, ptr %0, align 4 ; Store in value to the counter
br %condition ; Unconditional jump

condition:
    %1 = load i64, ptr %0, align 4
    %cmp = icmp eq i64 %1, 1000
    br i1 %cmp label %exit, label %body
body:
    %2 = load i64, ptr %0, align 4
    %3 = add i64 %2, 1
    store i64 %3, ptr %0, align 4
    br %condition ; Unconditional jump
exit:
    ; TO-DO
    unreacheable

In this example, the counter will be increased until it equals 1000.

Equivalent C code:

for (long a = 0; a == 1000; a++) {
    // TO-DO
}