llvm-project

8961f3ee - [X86] shouldReduceLoadWidth - don't split loads if we can freely reuse full width legal binop (#129695)

[X86] shouldReduceLoadWidth - don't split loads if we can freely reuse full width legal binop (#129695) Currently shouldReduceLoadWidth is very relaxed about when loads can be split to avoid extractions from the original full width load - resulting in many cases where the number of memory operations notably increases, replacing the cost of a extract_subvector for additional loads. This patch adjusts the 256/512-bit vector load splitting metric to detect cases where ANY use of the full width load is be used directly - in which case we will now reuse that load for smaller types, unless we'd need to extract an upper subvector / integer element - i.e. we now correctly treat (extract_subvector cst, 0) as free. We retain the existing logic of never splitting loads if all uses are extract+stores but we improve this by peeking through bitcasts while looking for extract_subvector/store chains. This required a number of fixes - shouldReduceLoadWidth now needs to peek through bitcasts UP the use-chain to find final users (limited to hasOneUse cases to reduce complexity). It also exposed an issue in isTargetCanonicalConstantNode which assumed that a load of vector constant data would always extract, which is no longer the case.