[LLVMdev] Why extra 4 bytes on stack ???

[Duncan Sands]

Hi Alexander,

> For some reason even the simplest "int main() { return 0; }" program
> allocates those four bytes:
>
> ; ModuleID = '/tmp/webcompile/_29079_0.bc'
> 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-unknown-linux-gnu"
>
> define i32 @main() nounwind uwtable {
>    %1 = alloca i32, align 4
>    store i32 0, i32* %1
>    ret i32 0
> }

this is a clang oddity (dragonegg doesn't do this).  Presumably the clang
developers found it convenient to do this.  It doesn't matter since the
optimizers will zap the useless alloca.

Ciao, Duncan.