[LLVMdev] instruction combiner patch

[Nick Lewycky]

I once wrote:

> I've patched the instruction combiner to return UndefValue when the
> index is constant and known to be out of range for either an ArrayType
> or PackedType.

That patch had to be removed as it broke SPEC. I've since updated the
patch, and am ready to break spec again. ;-) This patch adds constant
folding of multidimensional arrays even when the index to those arrays
is a single value, ala:

  int x[2][2] = { {40, 41}, {42, 43} };
  int *y = x;
  return y[2];

becomes:

  return 42;

Similarly, it also generates undef on out of range arrays, but only if
it's out of the range of the whole multi-dimensional array this time.

Patch attached.

Nick Lewycky

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