PromoteMem2Reg: use poison instead of undef as placeholder in phi entries from unreachable predecessors [NFC]

Author: nunoplopes

llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp

@@ -835,7 +835,7 @@ void PromoteMem2Reg::run() {
   // code.  Unfortunately, there may be unreachable blocks which the renamer
   // hasn't traversed.  If this is the case, the PHI nodes may not
   // have incoming values for all predecessors.  Loop over all PHI nodes we have
-  // created, inserting undef values if they are missing any incoming values.
+  // created, inserting poison values if they are missing any incoming values.
   for (DenseMap<std::pair<unsigned, unsigned>, PHINode *>::iterator
            I = NewPhiNodes.begin(),
            E = NewPhiNodes.end();
@@ -885,9 +885,9 @@ void PromoteMem2Reg::run() {
     BasicBlock::iterator BBI = BB->begin();
     while ((SomePHI = dyn_cast<PHINode>(BBI++)) &&
            SomePHI->getNumIncomingValues() == NumBadPreds) {
-      Value *UndefVal = UndefValue::get(SomePHI->getType());
+      Value *PoisonVal = PoisonValue::get(SomePHI->getType());
       for (BasicBlock *Pred : Preds)
-        SomePHI->addIncoming(UndefVal, Pred);
+        SomePHI->addIncoming(PoisonVal, Pred);
     }
   }
 

llvm/test/Transforms/Mem2Reg/undef-order.ll

@@ -45,7 +45,7 @@ define i32 @foo() {
 ; CHECK:       Block16:
 ; CHECK-NEXT:    br label [[JOIN]]
 ; CHECK:       Join:
-; CHECK-NEXT:    [[VAL_0:%.*]] = phi i32 [ 1, [[STORE1]] ], [ 2, [[STORE2]] ], [ undef, [[BLOCK1:%.*]] ], [ undef, [[BLOCK2:%.*]] ], [ undef, [[BLOCK3:%.*]] ], [ undef, [[BLOCK4:%.*]] ], [ undef, [[BLOCK5:%.*]] ], [ undef, [[BLOCK6:%.*]] ], [ undef, [[BLOCK7:%.*]] ], [ undef, [[BLOCK8:%.*]] ], [ undef, [[BLOCK9:%.*]] ], [ undef, [[BLOCK10:%.*]] ], [ undef, [[BLOCK11:%.*]] ], [ undef, [[BLOCK12:%.*]] ], [ undef, [[BLOCK13:%.*]] ], [ undef, [[BLOCK14:%.*]] ], [ undef, [[BLOCK15:%.*]] ], [ undef, [[BLOCK16:%.*]] ]
+; CHECK-NEXT:    [[VAL_0:%.*]] = phi i32 [ 1, [[STORE1]] ], [ 2, [[STORE2]] ], [ poison, [[BLOCK1:%.*]] ], [ poison, [[BLOCK2:%.*]] ], [ poison, [[BLOCK3:%.*]] ], [ poison, [[BLOCK4:%.*]] ], [ poison, [[BLOCK5:%.*]] ], [ poison, [[BLOCK6:%.*]] ], [ poison, [[BLOCK7:%.*]] ], [ poison, [[BLOCK8:%.*]] ], [ poison, [[BLOCK9:%.*]] ], [ poison, [[BLOCK10:%.*]] ], [ poison, [[BLOCK11:%.*]] ], [ poison, [[BLOCK12:%.*]] ], [ poison, [[BLOCK13:%.*]] ], [ poison, [[BLOCK14:%.*]] ], [ poison, [[BLOCK15:%.*]] ], [ poison, [[BLOCK16:%.*]] ]
 ; CHECK-NEXT:    ret i32 [[VAL_0]]
 ;
 Entry: