Fix an invalid bitcast crash that occurs when doing a partial memset of a vector

alloca. Fixes part of <rdar://problem/9580800>.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@133336 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/ScalarReplAggregates.cpp

@@ -521,10 +521,22 @@ bool ConvertToScalarInfo::CanConvertToScalar(Value *V, uint64_t Offset) {
     // If this is a constant sized memset of a constant value (e.g. 0) we can
     // handle it.
     if (MemSetInst *MSI = dyn_cast<MemSetInst>(User)) {
-      // Store of constant value and constant size.
-      if (!isa<ConstantInt>(MSI->getValue()) ||
-          !isa<ConstantInt>(MSI->getLength()))
+      // Store of constant value.
+      if (!isa<ConstantInt>(MSI->getValue()))
         return false;
+
+      // Store of constant size.
+      ConstantInt *Len = dyn_cast<ConstantInt>(MSI->getLength());
+      if (!Len)
+        return false;
+
+      // If the size differs from the alloca, we can only convert the alloca to
+      // an integer bag-of-bits.
+      // FIXME: This should handle all of the cases that are currently accepted
+      // as vector element insertions.
+      if (Len->getZExtValue() != AllocaSize || Offset != 0)
+        ScalarKind = Integer;
+
       IsNotTrivial = true;  // Can't be mem2reg'd.
       HadNonMemTransferAccess = true;
       continue;