Large stack displacements can sometimes take the stack out of bounds

[davidchisnall]

Compiling this function, the stack allocation for buf is done as:

800087b2: 6505          lui a0, 0x1 
800087b4: 22a1055b      ct.cincoffset   a0, sp, a0
800087b8: 8585155b      ct.cincoffset   a0, a0, -0x7a8

The first ct.cincoffset (which, unrelated, should be called cincaddr) takes sp out of bounds. The second brings it in, but by then the tag is cleared.

[resistor]

#283