Ignore unreachable blocks when doing memory dependence analysis on non-local

loads. It's not really profitable and may result in GVN going into an infinite
loop when it hits constructs like this:

     %x = gep %some.type %x, ...

Found via an LTO build of LLVM.

llvm-svn: 166490

llvm/lib/Analysis/MemoryDependenceAnalysis.cpp

@@ -983,7 +983,7 @@ getNonLocalPointerDepFromBB(const PHITransAddr &Pointer,
     for (NonLocalDepInfo::iterator I = Cache->begin(), E = Cache->end();
          I != E; ++I) {
       Visited.insert(std::make_pair(I->getBB(), Addr));
-      if (!I->getResult().isNonLocal())
+      if (!I->getResult().isNonLocal() && DT->isReachableFromEntry(I->getBB()))
         Result.push_back(NonLocalDepResult(I->getBB(), I->getResult(), Addr));
     }
     ++NumCacheCompleteNonLocalPtr;
@@ -1029,7 +1029,7 @@ getNonLocalPointerDepFromBB(const PHITransAddr &Pointer,
                                                  NumSortedEntries);
       
       // If we got a Def or Clobber, add this to the list of results.
-      if (!Dep.isNonLocal()) {
+      if (!Dep.isNonLocal() && DT->isReachableFromEntry(BB)) {
         Result.push_back(NonLocalDepResult(BB, Dep, Pointer.getAddr()));
         continue;
       }

llvm/test/Transforms/GVN/crash.ll

@@ -163,3 +163,39 @@ entry:
   ret i8 %1
 }
 
+
+; Test that a GEP in an unreachable block with the following form doesn't crash
+; GVN:
+;
+;    %x = gep %some.type %x, ...
+
+%struct.type = type { i64, i32, i32 }
+
+define fastcc void @func() nounwind uwtable ssp align 2 {
+entry:
+  br label %reachable.bb
+
+;; Unreachable code.
+
+unreachable.bb:
+  %gep.val = getelementptr inbounds %struct.type* %gep.val, i64 1
+  br i1 undef, label %u2.bb, label %u1.bb
+
+u1.bb:
+  %tmp1 = getelementptr inbounds %struct.type* %gep.val, i64 0, i32 0
+  store i64 -1, i64* %tmp1, align 8
+  br label %unreachable.bb
+
+u2.bb:
+  %0 = load i32* undef, align 4
+  %conv.i.i.i.i.i = zext i32 %0 to i64
+  br label %u2.bb
+
+;; Reachable code.
+
+reachable.bb:
+  br label %r1.bb
+
+r1.bb:
+  br label %u2.bb
+}