I'm currently working on programming language compiler that generated LLVM-IR. I'm not using any library for the emitting, so I'm just writing instructions to a file. The problem is mutable variables, I'm registering a %i, %i.(index)
with the value and then loading %i
with %i.(index)
. This may not be the right way to have mutable variables in llvm, but is the best of what I've tried before as i need them to work with recursion for example when looping over i as long as the value is less than ten which is what this code does.
LLVM out code:
@.str_0 = private unnamed_addr constant [4 x i8] c"%i\0A\00"
declare i32 @printf(i8*, ...) nounwind
define i32 @add(i32 %a, i32 %b) nounwind {
entry:
%t1 = add i32 %a, %b
ret i32 %t1
}
define i32 @main() nounwind {
entry:
%i = alloca i32
%i.0 = alloca i32
store i32 0, i32* %i.0
store i32 %i.0, i32* %i
%t2 = icmp slt i32 %i, 10
br i1 %t2, label %lb1, label %lb2
lb1:
%t3 = getelementptr [4 x i8], [4 x i8]* @.str_0, i32 0, i32 0
%t4 = call i32 @printf(i8* %t3, i32 %i)
%t5 = call i32 @add(i32 %i, i32 1)
%i.1 = alloca i32
store i32 %t5, i32* %i
store i32 %i.1, i32* %i
%t6 = icmp slt i32 %i, 10
br i1 %t6, label %lb1, label %lb2
lb2:
ret i32 0
}
The code my compiler is generating from:
fn add(a: int, b: int): int {
return a + b;
}
fn main(): void {
let i: int = 0;
while (i < 10) {
printf("%i\n", i);
i = add(i, 1);
}
return;
}
Error:
./out/test.zk.ll:15:15: error: '%i.0' defined with type 'ptr' but expected 'i32'
15 | store i32 %i.0, i32* %i
| ^
1 error generated.
I expect to be able to define a mutable variable then change it's value after the fact with it working in recursion.
Thanks in advance for any help.
You only need to manipulate the pointer from %i = alloca i32 in the LLVM IR, use load when read it, and store when updating it.
there is a similar loop example while tests , it generate the IR code below.
define i32 @test_func(i32 %x, i32 %y) {
entry:
%0 = alloca i32, align 4
%1 = alloca i32, align 4
store i32 %x, ptr %1, align 4
%2 = alloca i32, align 4
store i32 %y, ptr %2, align 4
br label %while_cond_0
while_cond_0: ; preds = %while_body_0, %entry
%3 = load i32, ptr %1, align 4
%4 = icmp sgt i32 %3, 0
br i1 %4, label %while_body_0, label %while_end_0
while_body_0: ; preds = %while_cond_0
%5 = load i32, ptr %2, align 4
%6 = add i32 %5, 10
store i32 %6, ptr %2, align 4
%7 = load i32, ptr %1, align 4
%8 = sub i32 %7, 1
store i32 %8, ptr %1, align 4
br label %while_cond_0
while_end_0: ; preds = %while_cond_0
%9 = load i32, ptr %2, align 4
store i32 %9, ptr %0, align 4
br label %exit
exit: ; preds = %while_end_0
%10 = load i32, ptr %0, align 4
ret i32 %10
}