LoopVectorize: Don't hang forever if a PHI only has skipped PHI uses.

Fixes PR15384.

llvm-svn: 176366

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -2724,6 +2724,9 @@ bool LoopVectorizationLegality::AddReductionVar(PHINode *Phi,
     // Is this a bin op ?
     FoundBinOp |= !isa<PHINode>(Iter);
 
+    // Remember the current instruction.
+    Instruction *OldIter = Iter;
+
     // For each of the *users* of iter.
     for (Value::use_iterator it = Iter->use_begin(), e = Iter->use_end();
          it != e; ++it) {
@@ -2749,7 +2752,7 @@ bool LoopVectorizationLegality::AddReductionVar(PHINode *Phi,
       if (isa<PHINode>(Iter) && isa<PHINode>(U) &&
           U->getParent() != TheLoop->getHeader() &&
           TheLoop->contains(U) &&
-          Iter->getNumUses() > 1)
+          Iter->hasNUsesOrMore(2))
         continue;
 
       // We can't have multiple inside users.
@@ -2769,6 +2772,10 @@ bool LoopVectorizationLegality::AddReductionVar(PHINode *Phi,
       Iter = U;
     }
 
+    // If all uses were skipped this can't be a reduction variable.
+    if (Iter == OldIter)
+      return false;
+
     // We found a reduction var if we have reached the original
     // phi node and we only have a single instruction with out-of-loop
     // users.

llvm/test/Transforms/LoopVectorize/phi-hang.ll

@@ -0,0 +1,29 @@
+; RUN: opt -S -loop-vectorize < %s
+
+; PR15384
+define void @test1(i32 %arg) {
+bb:
+  br label %bb1
+
+bb1:                                              ; preds = %bb5, %bb
+  %tmp = phi i32 [ 1, %bb ], [ %tmp7, %bb5 ]
+  %tmp2 = phi i32 [ %arg, %bb ], [ %tmp9, %bb5 ]
+  br i1 true, label %bb5, label %bb3
+
+bb3:                                              ; preds = %bb1
+  br label %bb4
+
+bb4:                                              ; preds = %bb3
+  br label %bb5
+
+bb5:                                              ; preds = %bb4, %bb1
+  %tmp6 = phi i32 [ 0, %bb4 ], [ %tmp, %bb1 ]
+  %tmp7 = phi i32 [ 0, %bb4 ], [ %tmp6, %bb1 ]
+  %tmp8 = phi i32 [ 0, %bb4 ], [ %tmp, %bb1 ]
+  %tmp9 = add nsw i32 %tmp2, 1
+  %tmp10 = icmp eq i32 %tmp9, 0
+  br i1 %tmp10, label %bb11, label %bb1
+
+bb11:                                             ; preds = %bb5
+  ret void
+}