llvm global constructors

ctor.cpp

#include <cstdio>

struct Foo
{
    Foo()
    {
        puts("Hello, ");
    }
};

Foo foo;

int main()
{
    puts("World!");
}

ctor.ll

; ModuleID = 'ctor.cpp'
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
target triple = "x86_64-pc-linux-gnu"

%struct.Foo = type { i8 }

@foo = global %struct.Foo zeroinitializer, align 1
@.str = private unnamed_addr constant [7 x i8] c"World!\00", align 1
@.str1 = private unnamed_addr constant [8 x i8] c"Hello, \00", align 1
;
; THIS IS THE IMPORTANT THING
;
@llvm.global_ctors = appending global [1 x { i32, void ()* }] [{ i32, void ()* } { i32 65535, void ()* @_GLOBAL__I_a }]

define internal void @__cxx_global_var_init() section ".text.startup" {
  call void @_ZN3FooC2Ev(%struct.Foo* @foo)
  ret void
}

; Function Attrs: uwtable
define linkonce_odr void @_ZN3FooC2Ev(%struct.Foo* %this) unnamed_addr #0 align 2 {
  %1 = alloca %struct.Foo*, align 8
  store %struct.Foo* %this, %struct.Foo** %1, align 8
  %2 = load %struct.Foo** %1
  %3 = call i32 @puts(i8* getelementptr inbounds ([8 x i8]* @.str1, i32 0, i32 0))
  ret void
}

; Function Attrs: uwtable
define i32 @main() #0 {
  %1 = call i32 @puts(i8* getelementptr inbounds ([7 x i8]* @.str, i32 0, i32 0))
  ret i32 0
}

declare i32 @puts(i8*) #1

define internal void @_GLOBAL__I_a() section ".text.startup" {
  call void @__cxx_global_var_init()
  ret void
}

attributes #0 = { uwtable "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
attributes #1 = { "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }

!llvm.ident = !{!0}

!0 = metadata !{metadata !"Debian clang version 3.4-2 (tags/RELEASE_34/final) (based on LLVM 3.4)"}