[llvm] Swap UnrollAndJam Pass to before the SLP Vectorizer Pass (PR #97029)

[Yashwant Singh via llvm-commits]

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@@ -1306,6 +1307,12 @@ void PassBuilder::addVectorPasses(OptimizationLevel Level,
     FPM.addPass(BDCEPass());
   }
 
+  // We do UnrollAndJam in a separate LPM to Unroll ensure it happens first.
+  // In order for outer loop vectorization to be done, UnrollAndJam must occur before the SLPVectorizerPass.
+  if (EnableUnrollAndJam && PTO.LoopUnrolling) {
+    FPM.addPass(createFunctionToLoopPassAdaptor(
+        LoopUnrollAndJamPass(Level.getSpeedupLevel())));
+  }
   // Optimize parallel scalar instruction chains into SIMD instructions.
   if (PTO.SLPVectorization) {
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yashssh wrote:

Is SLP vectorization on be default? If not then instead of moving UnJ, running another instance of the pass under this condition can be explored to avoid compile time penalties?

https://github.com/llvm/llvm-project/pull/97029