[PATCH] D99719: [SLP] Better estimate cost of no-op extracts on target vectors.

[Alexey Bataev via Phabricator via llvm-commits]

ABataev added inline comments.


================
Comment at: llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp:3457-3459
+InstructionCost
+BoUpSLP::computeExtractCostForPermuteSingleSrc(ArrayRef<Value *> VL,
+                                               FixedVectorType *VecTy) {
----------------
Can you make it static local?


================
Comment at: llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp:3462-3464
+  // Compute the number of number of elements per vector register for
+  // VecTy. If that is not possible, because the number of parts for VecTy
+  // is unknown, the number of elements.
----------------
Is this possible? Or better to make it an assert?


================
Comment at: llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp:3481-3485
+    ExtractElementInst *CurrentExtract = cast<ExtractElementInst>(V);
+    auto *IO = cast<ConstantInt>(CurrentExtract->getIndexOperand());
+    ExtractElementInst *PrevExtract = cast<ExtractElementInst>(VL[Idx - 1]);
+    unsigned PrevIdx =
+        cast<ConstantInt>(PrevExtract->getIndexOperand())->getZExtValue();
----------------
Use `*getExtractIndex(cast<Instruction>(V));` to get the indeces


================
Comment at: llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp:3508-3509
+    unsigned StartIdx = Idx - EltsPerVector + 1;
+    Optional<TargetTransformInfo::ShuffleKind> ShuffleKind =
+        isShuffle({&VL[StartIdx], VL.size() - StartIdx}, Mask);
+    assert(ShuffleKind && "Shuffle kind should always be computable");
----------------
1. 
```
   Optional<TargetTransformInfo::ShuffleKind> ShuffleKind = isShuffle(VL.slice(StartIdx, std::min(EltsPerVector, VL.size() - StartIdx)), Mask);
```
2. Can we skip this call? Just `TargetTransformInfo::SK_PermuteSingleSrc` and `None` as a `Mask`?


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D99719/new/

https://reviews.llvm.org/D99719