[Loads] Properly populate the visited set in isDereferenceableAndAlig…

…nedPointer

There were paths where we wouldn't populate the visited set, causing us
to recurse forever if an SSA variable was defined in terms of itself.

This fixes PR30210.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@280191 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/Loads.cpp

@@ -55,6 +55,10 @@ static bool isDereferenceableAndAlignedPointer(
     const Value *V, unsigned Align, const APInt &Size, const DataLayout &DL,
     const Instruction *CtxI, const DominatorTree *DT,
     SmallPtrSetImpl<const Value *> &Visited) {
+  // Already visited?  Bail out, we've likely hit unreachable code.
+  if (!Visited.insert(V).second)
+    return false;
+
   // Note that it is not safe to speculate into a malloc'd region because
   // malloc may return null.
 
@@ -87,8 +91,7 @@ static bool isDereferenceableAndAlignedPointer(
     // then the GEP (== Base + Offset == k_0 * Align + k_1 * Align) is also
     // aligned to Align bytes.
 
-    return Visited.insert(Base).second &&
-           isDereferenceableAndAlignedPointer(Base, Align, Offset + Size, DL,
+    return isDereferenceableAndAlignedPointer(Base, Align, Offset + Size, DL,
                                               CtxI, DT, Visited);
   }