[llvm] [LV][AArch64] Prefer epilogue with fixed-width over scalable VF in case of equal costs. (PR #155546)

[David Sherwood via llvm-commits]

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@@ -11,7 +11,7 @@ target triple = "aarch64-linux-gnu"
 
 ; DEBUG: LV: Checking a loop in 'main_vf_vscale_x_16'
 ; DEBUG: Create Skeleton for epilogue vectorized loop (first pass)
-; DEBUG: Main Loop VF:vscale x 16, Main Loop UF:2, Epilogue Loop VF:vscale x 8, Epilogue Loop UF:1
+; DEBUG: Main Loop VF:vscale x 16, Main Loop UF:2, Epilogue Loop VF:8, Epilogue Loop UF:1
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david-arm wrote:

Also, I think it's probably worth adding a variant of the first RUN line where we set the flag `-sve-prefer-fixed-over-scalable-if-equal=false` just to defend the selection of scalable VFs for the epilogue.

https://github.com/llvm/llvm-project/pull/155546