[GVN] Refactor analyzeLoadFromClobberingWrite to simplify code

[ksyx]

Summary

This change adjusts the order of two swappable if statements to make code cleaner.

[lattner]

nice thanks

[nikic]

llvm/lib/Transforms/Utils/VNCoercion.cpp

191–192

You may want to move this comment down, as it belongs to the moved condition.

llvm/lib/Transforms/Utils/VNCoercion.cpp

if (isFirstClassAggregateOrScalableType(LoadTy))
     return -1;
 
   int64_t StoreOffset = 0, LoadOffset = 0;
   Value *StoreBase =
       GetPointerBaseWithConstantOffset(WritePtr, StoreOffset, DL);
   Value *LoadBase = GetPointerBaseWithConstantOffset(LoadPtr, LoadOffset, DL);
   if (StoreBase != LoadBase)
     return -1;
 
-  // If the load and store are to the exact same address, they should have been
-  // a must alias.  AA must have gotten confused.
-  // FIXME: Study to see if/when this happens.  One case is forwarding a memset
-  // to a load from the base of the memset.
-
-  // If the load and store don't overlap at all, the store doesn't provide
-  // anything to the load.  In this case, they really don't alias at all, AA
-  // must have gotten confused.
   uint64_t LoadSize = DL.getTypeSizeInBits(LoadTy).getFixedSize();
 
   if ((WriteSizeInBits & 7) | (LoadSize & 7))
     return -1;
   uint64_t StoreSize = WriteSizeInBits / 8; // Convert to bytes.
   LoadSize /= 8;
 
-  bool isAAFailure = false;
-  if (StoreOffset < LoadOffset)
-    isAAFailure = StoreOffset + int64_t(StoreSize) <= LoadOffset;
-  else
-    isAAFailure = LoadOffset + int64_t(LoadSize) <= StoreOffset;
-
-  if (isAAFailure)
-    return -1;
-
   // If the Load isn't completely contained within the stored bits, we don't
   // have all the bits to feed it.  We could do something crazy in the future
   // (issue a smaller load then merge the bits in) but this seems unlikely to be
   // valuable.
   if (StoreOffset > LoadOffset ||
       StoreOffset + StoreSize < LoadOffset + LoadSize)
     return -1;
 
+  // If the load and store are to the exact same address, they should have been
+  // a must alias.  AA must have gotten confused.
+  // FIXME: Study to see if/when this happens.  One case is forwarding a memset
+  // to a load from the base of the memset.
+
+  // If the load and store don't overlap at all, the store doesn't provide
+  // anything to the load.  In this case, they really don't alias at all, AA
+  // must have gotten confused.  The if statement above ensure the condition
+  // that StoreOffset <= LoadOffset.
+  if (StoreOffset + int64_t(StoreSize) <= LoadOffset)
+    return -1;
+
   // Okay, we can do this transformation.  Return the number of bytes into the
   // store that the load is.
   return LoadOffset - StoreOffset;
 }
 
 /// This function is called when we have a
 /// memdep query of a load that ends up being a clobbering store.
 int analyzeLoadFromClobberingStore(Type *LoadTy, Value *LoadPtr,