[llvm] [SLSR] Skipping rewriting based on liveness (PR #218470)

[Igor Wodiany via llvm-commits]

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@@ -1411,6 +1423,380 @@ bool StraightLineStrengthReduceLegacyPass::runOnFunction(Function &F) {
   return StraightLineStrengthReduce(DL, DT, SE, TTI).runOnFunction(F);
 }
 
+namespace {
+
+class RewriteFilter {
+  // Recondiser rewriting a basic block holding many distinct SLSR bases.
+
+  // Each basis contributes one extended live range no matter how many
+  // candidates are rewritten against it in a basic block.
+  // If the number of bases is above this threshold do a check if the
+  // liveness of the block has increase a lot by SLSR.
+  static constexpr unsigned MinDistinctBasisesToFilter = 16;
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IgWod wrote:

Thanks for the detailed explanation. I have no preference regarding using cl::opt, I guess we can leave it as it now and change it if there is a use case for that.

https://github.com/llvm/llvm-project/pull/218470