[NFC] LoopAccess: Move expressions close to usage

[hiraditya]

Summary

Avoids useless evaluation of these expressions.

[michaelmaitland]

LGTM :)

[fhahn]

LGTM< thanks!

llvm/lib/Analysis/LoopAccessAnalysis.cpp

void RuntimePointerChecking::tryToCreateDiffCheck(
 
   auto *SrcAR = dyn_cast<SCEVAddRecExpr>(Src->Expr);
   auto *SinkAR = dyn_cast<SCEVAddRecExpr>(Sink->Expr);
   if (!SrcAR || !SinkAR) {
     CanUseDiffCheck = false;
     return;
   }
 
-  const DataLayout &DL =
-      SinkAR->getLoop()->getHeader()->getModule()->getDataLayout();
   SmallVector<Instruction *, 4> SrcInsts =
       DC.getInstructionsForAccess(Src->PointerValue, Src->IsWritePtr);
   SmallVector<Instruction *, 4> SinkInsts =
       DC.getInstructionsForAccess(Sink->PointerValue, Sink->IsWritePtr);
   Type *SrcTy = getLoadStoreType(SrcInsts[0]);
   Type *DstTy = getLoadStoreType(SinkInsts[0]);
   if (isa<ScalableVectorType>(SrcTy) || isa<ScalableVectorType>(DstTy)) {
     CanUseDiffCheck = false;
     return;
   }
+  const DataLayout &DL =
+      SinkAR->getLoop()->getHeader()->getModule()->getDataLayout();
   unsigned AllocSize =
       std::max(DL.getTypeAllocSize(SrcTy), DL.getTypeAllocSize(DstTy));
-  IntegerType *IntTy =
-      IntegerType::get(Src->PointerValue->getContext(),
-                       DL.getPointerSizeInBits(CGI.AddressSpace));
 
   // Only matching constant steps matching the AllocSize are supported at the
   // moment. This simplifies the difference computation. Can be extended in the
   // future.
   auto *Step = dyn_cast<SCEVConstant>(SinkAR->getStepRecurrence(*SE));
   if (!Step || Step != SrcAR->getStepRecurrence(*SE) ||
       Step->getAPInt().abs() != AllocSize) {
     CanUseDiffCheck = false;
     return;
   }
 
+  IntegerType *IntTy =
+      IntegerType::get(Src->PointerValue->getContext(),
+                       DL.getPointerSizeInBits(CGI.AddressSpace));
+
   // When counting down, the dependence distance needs to be swapped.
   if (Step->getValue()->isNegative())
     std::swap(SinkAR, SrcAR);
 
   const SCEV *SinkStartInt = SE->getPtrToIntExpr(SinkAR->getStart(), IntTy);
   const SCEV *SrcStartInt = SE->getPtrToIntExpr(SrcAR->getStart(), IntTy);
   if (isa<SCEVCouldNotCompute>(SinkStartInt) ||
       isa<SCEVCouldNotCompute>(SrcStartInt)) {