Lower llvm intrinsics early

[bmanga]

• Lower the llvm intrinsics also ealy in the pipeline
• deal with the fallout in the tests
• Add test for LowerAddrSpaceCast cannot handle multiple llvm.memcpy #1355

The LowerAddrSpaceCast pass obfuscates all intrinsics calls, so the rest of the llvm pipeline doesn't recognize them.
Additionally, lowering early might mean that the subsituted code has a chance of getting optimized more aggressively.

The tests fallout is:

test/CPlusPlus/issue-357.cl

The old testCopyInstance2 is now optimized out (it was copying uninitialized memory). The test now initializes the data before the copy.

test/LLVMIntrinsics/descend_into_array.cl

The PR results in some instructions being re-ordered.

test/LLVMIntrinsics/memcpy_from_constant.cl

This seems to be a minor regression.
Instead of:

  %1 = getelementptr { [0 x float] }, ptr addrspace(1) %0, i32 0, i32 0, i32 0
  store float -2.000000e+00, ptr addrspace(1) %1, align 4, !dbg !40

the llvm ir before the producer is:

  %.elt = extractvalue [5 x float] [float -2.000000e+00, float -1.000000e+00, float 0.000000e+00, float 1.000000e+00, float 
  %1 = getelementptr { [0 x float] }, ptr addrspace(1) %0, i32 0, i32 0, i32 0
  store float %.elt, ptr addrspace(1) %1, align 4

This seems to be due to the HideConstantLoadsPass/UnhideConstantLoadsPass . Maybe it's too disruptive for the issue it was trying to fix? (#71)
I will open an issue for this regression.

This closes #1350 and #1355

[rjodinchr]

Why did you put this addPass outside of the if statement?

If we really want it outside, maybe put it before the comment, and add comment before it?

[bmanga]

I added it outside because it helps in general, and I thought it's somewhat a big change for it to just change due to generic address space.
I moved it more to the top of the pipeline with a comment

[rjodinchr]

Could you provide a test showing how it helps in general, it's not clear to me looking at the modified tests. test/LLVMIntrinsics/memcpy_from_constant.cl even tends to say that it is not helping.