[llvm] [SROA] Only try additional vector type candidates when needed (PR #77678)

[Jeffrey Byrnes via llvm-commits]

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@@ -2216,86 +2317,9 @@ static VectorType *isVectorPromotionViable(Partition &P, const DataLayout &DL) {
     }
   }
 
-  // If we didn't find a vector type, nothing to do here.
-  if (CandidateTys.empty())
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jrbyrnes wrote:

Logic change: 

Testing the new partial-sized LoadStoreTys for candidacy (CheckCandidateType) modifies the heuristics HaveCommonEltTy , HaveVecPtrTy.

Thus, our decision regarding the viability of exact-sized slices (checkVectorTypesForPromotion) is impacted by whether those CheckCandidateType have occured. 

https://github.com/llvm/llvm-project/pull/77678