[llvm] [LV] Increase vectorize-memory-check-threshold to 256 (PR #151712)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-vectorizers

@llvm/pr-subscribers-llvm-transforms

Author: Igor Kirillov (igogo-x86)

<details>
<summary>Changes</summary>

We have a benchmark with large loops that benefit from vectorisation; however, they currently require several thousands runtime checks due to the way `LoopAccessAnalysis` is implemented. I would like to improve LAA to enable vectorisation with significantly fewer checks - though still somewhat more than the current limit of 128. Before committing to this task, I need to know whether we can raise this threshold. I checked and found that increasing it to 256 caused no performance or compile-time regressions, including when using the benchmarks from https://llvm-compile-time-tracker.com/

---
Full diff: https://github.com/llvm/llvm-project/pull/151712.diff


1 Files Affected:

- (modified) llvm/lib/Transforms/Vectorize/LoopVectorize.cpp (+1-1) 


``````````diff
diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index 850c4a11edc67..45460003f4a4e 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -203,7 +203,7 @@ static cl::opt<unsigned> TinyTripCountVectorThreshold(
              "are incurred."));
 
 static cl::opt<unsigned> VectorizeMemoryCheckThreshold(
-    "vectorize-memory-check-threshold", cl::init(128), cl::Hidden,
+    "vectorize-memory-check-threshold", cl::init(256), cl::Hidden,
     cl::desc("The maximum allowed number of runtime memory checks"));
 
 // Option prefer-predicate-over-epilogue indicates that an epilogue is undesired,

``````````

</details>


https://github.com/llvm/llvm-project/pull/151712