[PATCH] D111630: [LoopVectorize][CostModel] Update cost model for fmuladd intrinsic

[Paul Walker via Phabricator via llvm-commits]

paulwalker-arm added inline comments.


================
Comment at: llvm/lib/Transforms/Vectorize/LoopVectorize.cpp:7261-7278
   // If we're using ordered reductions then we can just return the base cost
   // here, since getArithmeticReductionCost calculates the full ordered
   // reduction cost when FP reassociation is not allowed.
-  if (useOrderedReductions(RdxDesc))
-    return BaseCost;
+  if (useOrderedReductions(RdxDesc)) {
+    if (RdxDesc.getRecurrenceKind() != RecurKind::FMulAdd)
+      return BaseCost;
+    // For a call to the llvm.fmuladd intrinsic we need to add the cost of a
----------------
Perhaps I've misunderstood something? because this code looks more complicated (or perhaps just more verbose) than the previous patch.  I guess I'm struggling why different versions of `getArithmeticInstrCost` are being called between the two.  I just assumed you'd add something like:
```
   InstructionCost BaseCost = TTI.getArithmeticReductionCost(                        
       RdxDesc.getOpcode(), VectorTy, RdxDesc.getFastMathFlags(), CostKind);         
                                                                                    
+  // For llvm.fmuladd based reductions we must include the cost of the normal       
+  // vector fmul that will occur prior to the fadd reduction.                       
+  if (RdxDesc.getRecurrenceKind() == RecurKind::FMulAdd)                            
+    BaseCost += TTI.getArithmeticInstrCost(Instruction::FMul, VectorTy, CostKind);  

   // If we're using ordered reductions then we can just return the base cost
   // here, since getArithmeticReductionCost calculates the full ordered
   // reduction cost when FP reassociation is not allowed.
   if (useOrderedReductions(RdxDesc))                                                
     return BaseCost;  
```


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D111630/new/

https://reviews.llvm.org/D111630