Control Flow Lowering

If/else/while in source maps to labels + branches in IR.

If:

if (x > 0) y = 1; else y = -1;

↓

t1 = LOAD x
CMP_GT t2, t1, 0
BR_IF t2, L_then, L_else
L_then:
  STORE y, 1
  BR L_end
L_else:
  STORE y, -1
L_end:

While:

while (i < 10) i = i + 1;

↓

L_start:
  t1 = LOAD i
  CMP_LT t2, t1, 10
  BR_IF t2, L_body, L_end
L_body:
  t3 = LOAD i
  t4 = ADD t3, 1
  STORE i, t4
  BR L_start
L_end:

For:

for (i = 0; i < 10; i++) sum = sum + i;

↓ (desugar to while)

i = 0
L_start:
  CMP_LT t1, i, 10
  BR_IF t1, L_body, L_end
L_body:
  ...sum = sum + i...
L_inc:
  i = i + 1
  BR L_start
L_end:

Continue jumps to L_inc; break jumps to L_end.

Boolean short-circuit:

if (a && b) ...

↓

t1 = LOAD a
BR_IF_NOT t1, L_false
t2 = LOAD b
BR_IF_NOT t2, L_false
BR L_true
L_true:
  ...

Switch:

• Small dense range: jump table (indexed branch).
• Sparse: chain of comparisons or binary search.

Return:

• BR to a single epilogue label that does cleanup + return.
• Or split: each function exit has its own epilogue.

The IR makes control flow explicit. Optimizers analyze the graph.