The cost of a v2i64 multiply was special cased in D92208 as scalarized
into 4*extract + 2*insert + 2*mul. Scalarizing to/from gpr registers are
expensive though, and the cost wasn't high enough to prevent vectorizing
in places where it can be detrimental for performance. This increases it
so that the costs of copying to/from GPRs is increased to 2 each, with
the total cost increasing to 14. So long as umull/smull are handled
correctly (as in D123006) this seems to lead to better vectorization
factors and better performance.
Differential Revision: https://reviews.llvm.org/D123007
This was modeled to have a cost of 1, but since we do not have a MUL.2d this is
scalarized into vector inserts/extracts and scalar muls.
Motivating precommitted test is test/Transforms/SLPVectorizer/AArch64/mul.ll,
which we don't want to SLP vectorize.
Test Transforms/LoopVectorize/AArch64/extractvalue-no-scalarization-required.ll
unfortunately needed changing, but the reason is documented in
LoopVectorize.cpp:6855:
// The cost of executing VF copies of the scalar instruction. This opcode
// is unknown. Assume that it is the same as 'mul'.
which I will address next as a follow up of this.
Differential Revision: https://reviews.llvm.org/D92208
The cost-model is not getting the cost right for a mul with <2 x i64>
operands, i.e. we don't have a MUL.2d, and this is precommitting some
tests before adjusting this.
Simon Pilgrim