[GSoC] llvm.invariant.start tests

[coodie]

This PR introduces tests for changes in #6706.

[mppf]

We have some ongoing work with initializers. Can you add a local and global test using this pattern?

record A
{
  var a : int;
  proc init(arg:int) {
    a = arg;
    super.init();
  }
}

That will cause the compiler to follow some code paths that aren't exercised in your tests so far but which we expect to become widely used in the future.

[coodie]

@mppf
I'm not sure what should I test as initializers make creating new records differently:

Here is how constructors work (let me use pseudo LLVM IR for that):

%tmp = alloca %A_chpl;
%localConst = alloca %A_chpl;
call construct_A(%A_chpl* %tmp, i64 %arg);
store %A_chpl %tmp, %A_chpl* %localConst

and here is how initializers work:

%localConst = alloca %A_chpl;
call init_A(%A_chpl* %localConst, i64 %arg);

Thus there is no final store which would mark that this variable is constant from this point giving opportunity to mark it using llvm.invariant.start, my algorithm covers a lot of cases because chapel compiler uses store from temporary to final a lot while in this case it doesn't happen so it doesn't do that.

[mppf]

@coodie - right, so in other words:

1. we'll need to use another approach to put llvm.invariant.start after these init calls
2. the current approach just leaves this case alone (and in particular doesn't generate incorrect IR for it)

[mppf]

@coodie - could you please double-check that these tests pass the way you have written them? I'm seeing testing failures with the following ones when run with start_test in an LLVM configuration with this branch merged with master and with the llvm-invariant branch.

[Error matching program output for llvm/llvm-invariant/function_local_const]
[Error matching program output for llvm/llvm-invariant/global_const]
[Error matching program output for llvm/llvm-invariant/program_constructs]

[coodie]

I fixed that. These changes were related to tbaa, which generation was changed.