[PATCH] D30649: [SLP] Function for instruction cost calculation, NFC.

[Michael Kuperstein via Phabricator via llvm-commits]

mkuper added inline comments.


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Comment at: lib/Transforms/Vectorize/SLPVectorizer.cpp:420
+  /// VecTy are specified).
+  Optional<int> getCostOrDiff(unsigned Opcode, ArrayRef<Value *> VL,
+                              Type *ScalarTy, Type *VecTy = nullptr) const;
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This seems like a weird interface, for a couple of reasons:

1) It's somewhat vague - I'd expect different APIs to get a cost and to get the diffs.
2) It returns an Optional, but none of the uses actually check the returned value is valid. And when would you expect to return None anyway? Shouldn't we recognize any instruction here? If not, then do we expect to assert, or just silently decide the instruction will be scalarized?
3) Only the Call case actually wants the scalar and the vector costs separately, and I don't really understand why - it ends up subtracting them.

Splitting out a function that takes the vector and scalar type, and returns the difference, instead of having the subtraction repeated in every case, doesn't sound like a bad idea. Can you explain why this is an improvement over that, though?


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Comment at: lib/Transforms/Vectorize/SLPVectorizer.cpp:1929
       CallInst *CI = cast<CallInst>(VL0);
-      Intrinsic::ID ID = getVectorIntrinsicIDForCall(CI, TLI);
-
-      // Calculate the cost of the scalar and vector calls.
-      SmallVector<Type*, 4> ScalarTys, VecTys;
-      for (unsigned op = 0, opc = CI->getNumArgOperands(); op!= opc; ++op) {
-        ScalarTys.push_back(CI->getArgOperand(op)->getType());
-        VecTys.push_back(VectorType::get(CI->getArgOperand(op)->getType(),
-                                         VecTy->getNumElements()));
-      }
-
-      FastMathFlags FMF;
-      if (auto *FPMO = dyn_cast<FPMathOperator>(CI))
-        FMF = FPMO->getFastMathFlags();
-
-      int ScalarCallCost = VecTy->getNumElements() *
-          TTI->getIntrinsicInstrCost(ID, ScalarTy, ScalarTys, FMF);
+      int ScalarCallCost = getCostOrDiff(Opcode, VL, ScalarTy).getValue();
 
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Isn't the point of getCostOrDiff that you should be able to pass the vector and the scalar types, and get the difference? Why are you using two calls and then subtracting?


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Comment at: lib/Transforms/Vectorize/SLPVectorizer.cpp:4981
 
+  SmallVector<WeakVH, 4> ExtractInsts;
   for (BasicBlock::iterator it = BB->begin(), e = BB->end(); it != e; it++) {
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This looks unrelated.


https://reviews.llvm.org/D30649