[IndVars] Add test for crash exposed by D114650.

Author: fhahn

llvm/test/Transforms/IndVarSimplify/phi-select.ll

@@ -0,0 +1,51 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -passes=indvars -S  %s | FileCheck %s
+
+define void @test_phi_select() {
+; CHECK-LABEL: @test_phi_select(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[OUTER_HEADER:%.*]]
+; CHECK:       outer.header:
+; CHECK-NEXT:    br i1 false, label [[THEN:%.*]], label [[MERGE:%.*]]
+; CHECK:       then:
+; CHECK-NEXT:    br label [[MERGE]]
+; CHECK:       merge:
+; CHECK-NEXT:    br label [[INNER:%.*]]
+; CHECK:       inner:
+; CHECK-NEXT:    [[INNER_IV_NEXT:%.*]] = add nsw i64 0, 0
+; CHECK-NEXT:    br i1 false, label [[INNER]], label [[OUTER_LATCH:%.*]]
+; CHECK:       outer.latch:
+; CHECK-NEXT:    br i1 true, label [[EXIT:%.*]], label [[OUTER_HEADER]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %outer.header
+
+outer.header:
+  %iv = phi i64 [ 0, %entry ], [ %iv.next, %outer.latch ]
+  %iv.next.1 = add nsw i64 %iv, 1
+  %cmp.0 = icmp sgt i64 %iv, 50
+  br i1 %cmp.0, label %then, label %merge
+
+then:
+  br label %merge
+
+merge:
+  %iv.sel = phi i64 [ %iv, %outer.header ], [ %iv.next.1, %then ]
+  br label %inner
+
+inner:                                            ; preds = %inner, %outer.header.new
+  %inner.iv = phi i64 [ %iv.sel, %merge ], [ 0, %inner ]
+  %inner.iv.next = add nsw i64 0, 0
+  %ec.1 = icmp sgt i64 0, 0
+  br i1 %ec.1, label %inner, label %outer.latch
+
+outer.latch:
+  %iv.next = add nuw nsw i64 %iv, 1
+  %ec.2 = icmp ult i64 %iv.next, 1000
+  br i1 %ec.2, label %exit, label %outer.header
+
+exit:
+  ret void
+}