It assumed that the VF remains constant throughout the tree. That's not
always true. This meant that we could query the extraction cost for a
lane that is out of bounds.
While experimenting with re-vectorisation for AArch64, we ran into this
issue. We cannot add a proper AArch64 test as more changes would need to
be brought in.
This commit is only fixing the computation of VF and adding an assert.
Some tests were failing after adding the assert:
- foo() in llvm/test/Transforms/SLPVectorizer/X86/horizontal.ll
- test() in
llvm/test/Transforms/SLPVectorizer/X86/reduction-with-removed-extracts.ll
- test_with_extract() in
llvm/test/Transforms/SLPVectorizer/RISCV/segmented-loads.ll
adb6efeac9