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- global variables start with @, but registers a and local variables start with %.
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- global variables define pointer values not values.
- start all basic blocks must start with a label (functions automatically get one).
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int f(int n) {
if ( n<=1) return 1;
return n*f(n-1);
}
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declare i32 @printf(i8 *, ...)
define i32 @fact(i32 %n_arg) {
; init arg(s): n
%n = alloca i32
store i32 %n_arg, i32* %n
; if ( n<=1) return 1;
%r1 = load i32* %n
%r2 = add i32 1, 0
%r3 = icmp sle i32 %r1, %r2
br i1 %r3, label %true5, label %false5
true5:
; return 1;
%r4 = add i32 1, 0
ret i32 %r4
false5:
; return n*fact(n-1);
%r6 = load i32* %n
; fact(n-1)
%r7 = load i32* %n
%r8 = add i32 1, 0
%r9 = sub i32 %r7, %r8
%r10 = call i32(i32)* @fact(i32 %r9)
%r11 = mul i32 %r6, %r10
ret i32 %r11
ret i32 0 ; auto-generated and eliminated by LLVM
}
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And here's an example that messes with a local integer and a global array.
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