[PATCH] D48023: [SLPVectorizer] Tidyup isShuffle helper

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon created this revision.
RKSimon added reviewers: ABataev, dtemirbulatov, spatel.

Ensure we keep track of the input vectors in all cases instead of just for SK_Alternate (this will be more useful once https://reviews.llvm.org/D47985 has landed).

Ideally we'd reuse the shuffle mask pattern matching in TargetTransformInfo::getInstructionThroughput here to easily add support for all TargetTransformInfo::ShuffleKind without mass code duplication, I've added a TODO for now.


Repository:
  rL LLVM

https://reviews.llvm.org/D48023

Files:
  lib/Transforms/Vectorize/SLPVectorizer.cpp


Index: lib/Transforms/Vectorize/SLPVectorizer.cpp
===================================================================
--- lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -246,6 +246,8 @@
 /// %ins4 = insertelement <4 x i8> %ins3, i8 %9, i32 3
 /// ret <4 x i8> %ins4
 /// InstCombiner transforms this into a shuffle and vector mul
+/// TODO: Can we split off and reuse the shuffle mask detection from
+/// TargetTransformInfo::getInstructionThroughput?
 static Optional<TargetTransformInfo::ShuffleKind>
 isShuffle(ArrayRef<Value *> VL) {
   auto *EI0 = cast<ExtractElementInst>(VL[0]);
@@ -272,7 +274,11 @@
       continue;
     // For correct shuffling we have to have at most 2 different vector operands
     // in all extractelement instructions.
-    if (Vec1 && Vec2 && Vec != Vec1 && Vec != Vec2)
+    if (!Vec1 || Vec1 == Vec)
+      Vec1 = Vec;
+    else if (!Vec2 || Vec2 == Vec)
+      Vec2 = Vec;
+    else
       return None;
     if (CommonShuffleMode == Permute)
       continue;
@@ -283,10 +289,6 @@
       continue;
     }
     // Check the shuffle mode for the current operation.
-    if (!Vec1)
-      Vec1 = Vec;
-    else if (Vec != Vec1)
-      Vec2 = Vec;
     // Example: shufflevector A, B, <0,5,2,7>
     // I is odd and IntIdx for A == I - FirstAlternate shuffle.
     // I is even and IntIdx for B == I - FirstAlternate shuffle.


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