Replace constant conditional branches by unconditional branches

src/IceCfgNode.cpp

Index: src/IceCfgNode.cpp
diff --git a/src/IceCfgNode.cpp b/src/IceCfgNode.cpp
index a87642d14c78a72370a6cd4393dfd8c3bc3141a0..f49a2171ae6e0472d1d67dd270ec16d863645f31 100644
--- a/src/IceCfgNode.cpp
+++ b/src/IceCfgNode.cpp
@@ -106,8 +106,11 @@ void CfgNode::validatePhis() {
           break;
         }
       }
-      if (!Found)
-        llvm::report_fatal_error("Phi error: label for bad incoming edge");
+      if (!Found) {
+        // Predecessor was unreachable, so if (impossibly) the control flow
+        // enters from that predecessor, the value should be zero.
+        Phi->clearOperandForTarget(Label);
+      }
     }
     for (CfgNode *InNode : getInEdges()) {
       bool Found = false;