[llvm] d7ef34b - [LV] update comment following 63d8058 (NFC) (#91120)

[via llvm-commits]

Author: Ramkumar Ramachandra
Date: 2024-05-14T10:59:26+01:00
New Revision: d7ef34bfe3d432ffd66a05fc9fcc87fd6c3db2ee

URL: https://github.com/llvm/llvm-project/commit/d7ef34bfe3d432ffd66a05fc9fcc87fd6c3db2ee
DIFF: https://github.com/llvm/llvm-project/commit/d7ef34bfe3d432ffd66a05fc9fcc87fd6c3db2ee.diff

LOG: [LV] update comment following 63d8058 (NFC) (#91120)

Address a review comment post landing 63d8058 (LoopVectorize: guard
appending InstsToScalarize; fix bug) to update a comment.

Added: 
    

Modified: 
    llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

Removed: 
    


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diff  --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index ba02c98285c33..9353666e417c8 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -5813,10 +5813,11 @@ void LoopVectorizationCostModel::collectInstsToScalarize(ElementCount VF) {
     for (Instruction &I : *BB)
       if (isScalarWithPredication(&I, VF)) {
         ScalarCostsTy ScalarCosts;
-        // Do not apply discount if scalable, because that would lead to
-        // invalid scalarization costs.
-        // Do not apply discount logic if hacked cost is needed
-        // for emulated masked memrefs.
+        // Do not apply discount logic for:
+        // 1. Scalars after vectorization, as there will only be a single copy
+        // of the instruction.
+        // 2. Scalable VF, as that would lead to invalid scalarization costs.
+        // 3. Emulated masked memrefs, if a hacked cost is needed.
         if (!isScalarAfterVectorization(&I, VF) && !VF.isScalable() &&
             !useEmulatedMaskMemRefHack(&I, VF) &&
             computePredInstDiscount(&I, ScalarCosts, VF) >= 0)