[Test] Add more elaborate case of symbolic execution of 1-iteration loop

Author: xortator

llvm/test/Transforms/LoopDeletion/eval_first_iteration.ll

@@ -648,3 +648,78 @@ done:                                             ; preds = %backedge
 failure:
   unreachable
 }
+
+; TODO: We can break the backedge here.
+define i32 @test_multiple_pred_2() {
+; CHECK-LABEL: @test_multiple_pred_2(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[SUM_NEXT:%.*]], [[BACKEDGE:%.*]] ]
+; CHECK-NEXT:    [[SUB:%.*]] = sub i32 4, [[SUM]]
+; CHECK-NEXT:    [[IS_POSITIVE:%.*]] = icmp sgt i32 [[SUB]], 0
+; CHECK-NEXT:    br i1 [[IS_POSITIVE]], label [[IF_TRUE:%.*]], label [[IF_FALSE:%.*]]
+; CHECK:       if.true:
+; CHECK-NEXT:    br i1 undef, label [[IF_TRUE_1:%.*]], label [[IF_TRUE_2:%.*]]
+; CHECK:       if.true.1:
+; CHECK-NEXT:    br label [[BACKEDGE]]
+; CHECK:       if.true.2:
+; CHECK-NEXT:    br label [[BACKEDGE]]
+; CHECK:       if.false:
+; CHECK-NEXT:    br i1 undef, label [[IF_FALSE_1:%.*]], label [[IF_FALSE_2:%.*]]
+; CHECK:       if.false.1:
+; CHECK-NEXT:    br label [[BACKEDGE]]
+; CHECK:       if.false.2:
+; CHECK-NEXT:    br label [[BACKEDGE]]
+; CHECK:       backedge:
+; CHECK-NEXT:    [[MERGE_PHI:%.*]] = phi i32 [ 0, [[IF_FALSE_1]] ], [ 0, [[IF_FALSE_2]] ], [ [[SUB]], [[IF_TRUE_1]] ], [ [[SUB]], [[IF_TRUE_2]] ]
+; CHECK-NEXT:    [[SUM_NEXT]] = add i32 [[SUM]], [[MERGE_PHI]]
+; CHECK-NEXT:    [[LOOP_COND:%.*]] = icmp ne i32 [[SUM_NEXT]], 4
+; CHECK-NEXT:    br i1 [[LOOP_COND]], label [[LOOP]], label [[DONE:%.*]]
+; CHECK:       done:
+; CHECK-NEXT:    [[SUM_NEXT_LCSSA:%.*]] = phi i32 [ [[SUM_NEXT]], [[BACKEDGE]] ]
+; CHECK-NEXT:    ret i32 [[SUM_NEXT_LCSSA]]
+; CHECK:       failure:
+; CHECK-NEXT:    unreachable
+;
+entry:
+
+  br label %loop
+
+loop:                                             ; preds = %backedge, %entry
+  %sum = phi i32 [ 0, %entry ], [ %sum.next, %backedge ]
+  %sub = sub i32 4, %sum
+  %is.positive = icmp sgt i32 %sub, 0
+  br i1 %is.positive, label %if.true, label %if.false
+
+if.true:
+  br i1 undef, label %if.true.1, label %if.true.2
+
+if.true.1:
+  br label %backedge
+
+if.true.2:
+  br label %backedge
+
+if.false:                                         ; preds = %loop
+  br i1 undef, label %if.false.1, label %if.false.2
+
+if.false.1:
+  br label %backedge
+
+if.false.2:
+  br label %backedge
+
+backedge:
+  %merge.phi = phi i32 [ 0, %if.false.1 ], [ 0, %if.false.2 ], [ %sub, %if.true.1 ], [ %sub, %if.true.2 ]
+  %sum.next = add i32 %sum, %merge.phi
+  %loop.cond = icmp ne i32 %sum.next, 4
+  br i1 %loop.cond, label %loop, label %done
+
+done:                                             ; preds = %backedge
+  %sum.next.lcssa = phi i32 [ %sum.next, %backedge ]
+  ret i32 %sum.next.lcssa
+
+failure:
+  unreachable
+}