One of the vector splitting paths for extract_vector_elt tries to lower:

define i1 @via_stack_bug(i8 signext %idx) { %1 = extractelement <2 x i1> <i1 false, i1 true>, i8 %idx ret i1 %1 }

to:

define i1 @via_stack_bug(i8 signext %idx) { %base = alloca <2 x i1> store <2 x i1> <i1 false, i1 true>, <2 x i1>* %base %2 = getelementptr <2 x i1>, <2 x i1>* %base, i32 %idx %3 = load i1, i1* %2 ret i1 %3 }

However, the elements of <2 x i1> are not byte-addressible. The result of this

is that the getelementptr expands to '%base + %idx * (1 / 8)' which simplifies

to '%base + %idx * 0', and then simply '%base' causing all values of %idx to

extract element zero.

This commit fixes this by promoting the vector elements of <8-bits to i8 before

splitting the vector.

This fixes a number of test failures in pocl.