CODEWITHSUNDEEP
llvmllvm-ir
Nathan
Nathan

Reputation: 3205

LLVM Invalid return type of main() supplied

I'm writing a compiler in OCaml that compiles to LLVM IR. The current program is very simple:

num main() {
    return 0;
}

When I run it with my compiler, I get the following LLVM IR code:

; ModuleID = 'PixMix'
source_filename = "PixMix"

@fmt = private unnamed_addr constant [4 x i8] c"%d\0A\00"
@fmt.1 = private unnamed_addr constant [4 x i8] c"%s\0A\00"

declare i32 @printf(i8*, ...)

define double @main() {
entry:
  ret double 0.000000e+00
}

However, if I pass it to lli, I'm told that the return type is invalid. Looking at that code, main is defined as a double and it's returning a double, so why is lli telling me that the return type is messed up?

Upvotes: 2

Views: 444

Answers (1)

Ismail Badawi
Ismail Badawi

Reputation: 37227

The issue is that the entry point function (main by default, but the name can be controlled by the -entry-function flag) is expected to have a certain signature, similar to what main looks like in C or C++. In particular, it should either return void or an integer type. You can read the implementation of the check to make sure the IR you generate satisfies it.

Upvotes: 2

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