llvm-project

f803e463 - Reland "Redesign Straight-Line Strength Reduction (SLSR) (#162930)" (#169614)

Reland "Redesign Straight-Line Strength Reduction (SLSR) (#162930)" (#169614) This PR implements parts of https://github.com/llvm/llvm-project/issues/162376 - **Broader equivalence than constant index deltas**: - Add Base-delta and Stride-delta matching for Add and GEP forms using ScalarEvolution deltas. - Reuse enabled for both constant and variable deltas when an available IR value dominates the user. - **Dominance-aware dictionary instead of linear scans**: - Tuple-keyed candidate dictionary grouped by basic block. - Walk the immediate-dominator chain to find the nearest dominating basis quickly and deterministically. - **Simple cost model and best-rewrite selection**: - Score candidate expressions and rewrites; select the highest-profit rewrite per instruction. - Skip rewriting when expressions are already foldable or high-efficiency. - **Path compression for better ILP**: - Compress chains of rewrites to a deeper dominating basis when a constant delta exists along the path, reducing dependent bumps on critical paths. - **Dependency-aware rewrite ordering**: - Build a dependency graph (basis, stride, variable delta producers) and rewrite in topological order. - This dependency graph will be needed by the next PR that adds partial strength reduction. - **Correctness enhencment** - Fix a correctness issue that reusing instructions with the same SCEV may introduce poison. --------- Co-authored-by: Kazu Hirata <kazu@google.com>