This if-else condition inside the visit_Br() is not clear to me. @Thirumalai-Shaktivel, please, could you possibly share how this if-else works and chooses whether to iterate the loop or end it?

Consider this example:

while i < 10:
    j = 0
    while j < 10:
        k += 1
        if i == 0:
            if j == 3:
                continue
            else:
                j += 1
        j += 1
    i += 1
assert k == 95

Output printed using:

diff --git a/src/libasr/codegen/wasm_to_x86.cpp b/src/libasr/codegen/wasm_to_x86.cpp
index 9db9d2b4b..48f947076 100644
--- a/src/libasr/codegen/wasm_to_x86.cpp
+++ b/src/libasr/codegen/wasm_to_x86.cpp
@@ -131,6 +131,9 @@ class X86Visitor : public WASMDecoder<X86Visitor>,
     void visit_EmtpyBlockType() {}
 
     void visit_Br(uint32_t label_index) {
+std::cout << "label_index: " << label_index << "\n";
+std::cout << "Loop_size: " << loop_unique_id.size() << "\n";
+std::cout << "If_size: " << if_unique_id.size() << "\n";
         // Branch is used to jump to the `loop.head` or `loop.end`.

$ lpython examples/expr2.py --backend wasm_x86 && ./expr2.out
label_index: 3
Loop_size: 2
If_size: 4
label_index: 1
Loop_size: 2
If_size: 2
label_index: 1
Loop_size: 1
If_size: 1

We have 2 loops and 2 if's. But in the backend, we get 2 loops and 4 ifs, right?
The first br comes from the continue, if we subtract 4 if's with 2 loops: we get the actual 2 if's. the label_index is 3, we do 3 - 1 = 2: jump to head and So on...

But if the break is encountered the label_index is 2, So we jump to the end of the loop
Any doubts, please ask

how this if-else works and chooses whether to iterate the loop or end it?

Every time, the loop is iterated using the Br. Also, I didn't analyze how the loop is being exited. I will look into it soon.

I see, the Loop is exited through the else block:

.loop.head_297:
    mov eax, [ebp-4]
    push eax
    push 0x0000000a
    pop ebx
    pop eax
    cmp eax, ebx
    jl .compare_1303
    push 0x00
    jmp .compare.end_303
.compare_1303:
    push 0x01
.compare.end_303:
    pop eax
    cmp eax, 0x01
    je .then_304
    jmp .else_304
.then_304:
    mov eax, [ebp-4]
    push eax
    push 0x00000001
    pop ebx
    pop eax
    add eax, ebx
    push eax
    pop eax
    mov [ebp-4], eax
    jmp .loop.head_297
    jmp .endif_304
.else_304:
.endif_304:
.loop.end_297:
    mov esp, ebp
    pop ebp
    ret

I have a doubt, here the jump and label .endif_304 is useless? is it ok? @Shaikh-Ubaid

@Shaikh-Ubaid, were you able to understand or get the point?

I have a doubt, here the jump and label .endif_304 is useless? is it ok? @Shaikh-Ubaid

I think for the moment that should be fine.

@Shaikh-Ubaid, were you able to understand or get the point?

Yup, thank you so much for the explanation, Thirumalai.

It seems this condition (if_unique_id.size() - loop_unique_id.size() == label_index - 1) might not be perfect to determine to continue or end the loop. Consider the following example where we have a loop inside an if construct:

def main0():
    x: i32
    x = (2+3)*5
    j: i32 = 0
    if True:
        while x > 0:
            j += 2
            x -= 1
    print(x)
    print(j)

main0()

Output:

(lp) ubaid@ubaid-Lenovo-ideapad-330-15ARR:~/OpenSource/lpython$ lpython examples/expr2.py
0
50
(lp) ubaid@ubaid-Lenovo-ideapad-330-15ARR:~/OpenSource/lpython$ lpython examples/expr2.py --backend wasm_x86 -o loop
(lp) ubaid@ubaid-Lenovo-ideapad-330-15ARR:~/OpenSource/lpython$ ./loop 
24
2
(lp) ubaid@ubaid-Lenovo-ideapad-330-15ARR:~/OpenSource/lpython$ 

The loop in this case just executes once and then exits. This is because in this case (when visit_Br() is visited) the if count would be 2 and loop count would be 1. The label_index would be 1. The condition would be 2 - 1 == 1 - 1, that is 1 == 0, which is not true and hence the loop exits.

I think we might need to simulate how wasm works in x86. We might need to use same label indexes (or same label index space) for if's and loop's (just like wasm does).

It seems this condition (if_unique_id.size() - loop_unique_id.size() == label_index - 1) might not be perfect to determine to continue or end the loop.

+1; I agree with this.
Also, I didn't test the loop within the if statement.
There you go, you've found the actual bug in the loop statement.
Thank you for testing this. I will make this a new issue. Let's work on this and fix it.

Great note, Thirumalai !. It explains the loop structure very beautifully. Thank you so much for it.