[llvm] 3e8a8fc - ValueTracking: clarify isNotCrossLaneOperation (NFC) (#112375)

[via llvm-commits]

Author: Ramkumar Ramachandra
Date: 2024-11-04T15:54:06Z
New Revision: 3e8a8fce4aea14e7475c3ebf22227401e33bfe02

URL: https://github.com/llvm/llvm-project/commit/3e8a8fce4aea14e7475c3ebf22227401e33bfe02
DIFF: https://github.com/llvm/llvm-project/commit/3e8a8fce4aea14e7475c3ebf22227401e33bfe02.diff

LOG: ValueTracking: clarify isNotCrossLaneOperation (NFC) (#112375)

Clarify the distinction between lanewise operations, and operations that
do not cross vector lanes, with an example, in the header comment.

Added: 
    

Modified: 
    llvm/include/llvm/Analysis/ValueTracking.h

Removed: 
    


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diff  --git a/llvm/include/llvm/Analysis/ValueTracking.h b/llvm/include/llvm/Analysis/ValueTracking.h
index 0c6ebf87b29232..2b0377903ac8e3 100644
--- a/llvm/include/llvm/Analysis/ValueTracking.h
+++ b/llvm/include/llvm/Analysis/ValueTracking.h
@@ -791,7 +791,12 @@ bool onlyUsedByLifetimeMarkers(const Value *V);
 /// droppable instructions.
 bool onlyUsedByLifetimeMarkersOrDroppableInsts(const Value *V);
 
-/// Return true if the instruction doesn't potentially cross vector lanes.
+/// Return true if the instruction doesn't potentially cross vector lanes. This
+/// condition is weaker than checking that the instruction is lanewise: lanewise
+/// means that the same operation is splatted across all lanes, but we also
+/// include the case where there is a 
diff erent operation on each lane, as long
+/// as the operation only uses data from that lane. An example of an operation
+/// that is not lanewise, but doesn't cross vector lanes is insertelement.
 bool isNotCrossLaneOperation(const Instruction *I);
 
 /// Return true if the instruction does not have any effects besides