SROA: Only split loads on byte boundaries

r199771 accidently broke the logic that makes sure that SROA only splits
load on byte boundaries.  If such a split happens, some bits get lost
when reassembling loads of wider types, causing data corruption.

Move the width check up to reject such splits early, avoiding the
corruption.  Fixes PR19250.

Patch by: Björn Steinbrink <bsteinbr@gmail.com>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211082 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/SROA.cpp

@@ -1032,11 +1032,6 @@ static Type *findCommonType(AllocaSlices::const_iterator B,
       UserTy = SI->getValueOperand()->getType();
     }
 
-    if (!UserTy || (Ty && Ty != UserTy))
-      TyIsCommon = false; // Give up on anything but an iN type.
-    else
-      Ty = UserTy;
-
     if (IntegerType *UserITy = dyn_cast_or_null<IntegerType>(UserTy)) {
       // If the type is larger than the partition, skip it. We only encounter
       // this for split integer operations where we want to use the type of the
@@ -1051,6 +1046,13 @@ static Type *findCommonType(AllocaSlices::const_iterator B,
       if (!ITy || ITy->getBitWidth() < UserITy->getBitWidth())
         ITy = UserITy;
     }
+
+    // To avoid depending on the order of slices, Ty and TyIsCommon must not
+    // depend on types skipped above.
+    if (!UserTy || (Ty && Ty != UserTy))
+      TyIsCommon = false; // Give up on anything but an iN type.
+    else
+      Ty = UserTy;
   }
 
   return TyIsCommon ? Ty : ITy;