llvm-project

551ff98c - [SLP][TTI][AMDGPU] Add TTI hook preferSLPInstCountCheck for per-target opt-out (#199696)

[SLP][TTI][AMDGPU] Add TTI hook preferSLPInstCountCheck for per-target opt-out (#199696) Add `preferSLPInstCountCheck()` to TTI so targets can opt out of the 2-element inst-count heuristic in `getTreeCost()`. Default returns `true` (existing behavior unchanged). `getTreeCost()` ANDs the existing `SLPInstCountCheck` flag with the hook result. `GCNTTIImpl` returns `false` for gfx940/gfx941/gfx942 and gfx950. Fixes #199662.