Bad align argument on store instr for struct parameter

[tjhann]

LDC emits IR where a store with alignment of 8 writes to an alloca with alignment of 4. Overestimating the alignment causes undefined behaviour [0]. I tried with LDC 1.25.1 and LDC 1.24.0 on Ubuntu 20.04.2 LTS / x86-64 (Xubuntu, actually).
[0] https://llvm.org/docs/LangRef.html#id212

For this:

struct Box {
    int a;
    int b;
    int c;
}

void takebox(Box box) { }

void main()
{
    Box box;
    takebox(box);
}

I'm getting this code:

define void @_D3bug7takeboxFSQo3BoxZv({ i64, i32 } %box_arg) #0 {
  %.BaseBitcastABIRewrite_param_storage = alloca { i64, i32 }, align 4 ; [#uses = 2, size/byte = 16]
  store { i64, i32 } %box_arg, { i64, i32 }* %.BaseBitcastABIRewrite_param_storage, align 8 ; <-- BAD ALIGNMENT!
  %box = bitcast { i64, i32 }* %.BaseBitcastABIRewrite_param_storage to %bug.Box* ; [#uses = 0]
  ret void
}

[kinke]

Thx for reporting.