diff --git a/llvm/test/Transforms/LoopVectorize/smax-idx.ll b/llvm/test/Transforms/LoopVectorize/smax-idx.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/Transforms/LoopVectorize/smax-idx.ll
@@ -0,0 +1,234 @@
+; RUN: opt -passes=loop-vectorize -force-vector-width=4 -force-vector-interleave=1 -S < %s | FileCheck %s --check-prefix=CHECK
+; RUN: opt -passes=loop-vectorize -force-vector-width=4 -force-vector-interleave=4 -S < %s | FileCheck %s --check-prefix=CHECK
+; RUN: opt -passes=loop-vectorize -force-vector-width=1 -force-vector-interleave=4 -S < %s | FileCheck %s --check-prefix=CHECK
+
+define i64 @smax_idx(ptr nocapture readonly %a, i64 %mm, i64 %ii, ptr nocapture writeonly %res_max, i64 %n) {
+; CHECK-LABEL: @smax_idx(
+; CHECK-NOT:   vector.body:
+;
+entry:
+  br label %for.body
+
+for.body:
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %max.09 = phi i64 [ %mm, %entry ], [ %1, %for.body ]
+  %idx.011 = phi i64 [ %ii, %entry ], [ %spec.select7, %for.body ]
+  %arrayidx = getelementptr inbounds i64, ptr %a, i64 %indvars.iv
+  %0 = load i64, ptr %arrayidx
+  %1 = tail call i64 @llvm.smax.i64(i64 %max.09, i64 %0)
+  %cmp1 = icmp slt i64 %max.09, %0
+  %spec.select7 = select i1 %cmp1, i64 %indvars.iv, i64 %idx.011
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond.not = icmp eq i64 %indvars.iv.next, %n
+  br i1 %exitcond.not, label %exit, label %for.body
+
+exit:
+  store i64 %1, ptr %res_max
+  ret i64 %spec.select7
+}
+
+;
+; Check the different order of reduction phis.
+;
+define i64 @smax_idx_inverted_phi(ptr nocapture readonly %a, i64 %mm, i64 %ii, ptr nocapture writeonly %res_max, i64 %n) {
+; CHECK-LABEL: @smax_idx_inverted_phi(
+; CHECK-NOT:   vector.body:
+;
+entry:
+  br label %for.body
+
+for.body:
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %idx.011 = phi i64 [ %ii, %entry ], [ %spec.select7, %for.body ]
+  %max.09 = phi i64 [ %mm, %entry ], [ %1, %for.body ]
+  %arrayidx = getelementptr inbounds i64, ptr %a, i64 %indvars.iv
+  %0 = load i64, ptr %arrayidx
+  %1 = tail call i64 @llvm.smax.i64(i64 %max.09, i64 %0)
+  %cmp1 = icmp slt i64 %max.09, %0
+  %spec.select7 = select i1 %cmp1, i64 %indvars.iv, i64 %idx.011
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond.not = icmp eq i64 %indvars.iv.next, %n
+  br i1 %exitcond.not, label %exit, label %for.body
+
+exit:
+  store i64 %1, ptr %res_max
+  ret i64 %spec.select7
+}
+
+; Check if it is a MMI when smax is not used outside the loop.
+;
+; Currently at the end, it will check if smax has exitInstruction.
+; But in fact MMI should be possible to use the exitInstruction of
+; SelectICmp be the exitInstruction.
+;
+define i64 @smax_idx_max_no_exit_user(ptr nocapture readonly %a, i64 %mm, i64 %ii, i64 %n) {
+; CHECK-LABEL: @smax_idx_max_no_exit_user(
+; CHECK-NOT:   vector.body:
+;
+entry:
+  br label %for.body
+
+for.body:
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %max.09 = phi i64 [ %mm, %entry ], [ %1, %for.body ]
+  %idx.011 = phi i64 [ %ii, %entry ], [ %spec.select7, %for.body ]
+  %arrayidx = getelementptr inbounds i64, ptr %a, i64 %indvars.iv
+  %0 = load i64, ptr %arrayidx
+  %1 = tail call i64 @llvm.smax.i64(i64 %max.09, i64 %0)
+  %cmp1 = icmp slt i64 %max.09, %0
+  %spec.select7 = select i1 %cmp1, i64 %indvars.iv, i64 %idx.011
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond.not = icmp eq i64 %indvars.iv.next, %n
+  br i1 %exitcond.not, label %exit, label %for.body
+
+exit:
+  ; %1 has no external users
+  ret i64 %spec.select7
+}
+
+; Check smax implemented in terms of select(cmp()).
+;
+; Currently SelectICmp does not support icmp with multiple users.
+; It may be possible to reuse some of the methods in Combination pass to check
+; whether icmp can be copied.
+;
+define i64 @smax_idx_select_cmp(ptr nocapture readonly %a, i64 %mm, i64 %ii, ptr nocapture writeonly %res_max, i64 %n) {
+; CHECK-LABEL: @smax_idx_select_cmp(
+; CHECK-NOT:   vector.body:
+;
+entry:
+  br label %for.body
+
+for.body:
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %max.09 = phi i64 [ %mm, %entry ], [ %spec.select, %for.body ]
+  %idx.011 = phi i64 [ %ii, %entry ], [ %spec.select7, %for.body ]
+  %arrayidx = getelementptr inbounds i64, ptr %a, i64 %indvars.iv
+  %0 = load i64, ptr %arrayidx
+  %cmp1 = icmp slt i64 %max.09, %0
+  %spec.select = select i1 %cmp1, i64 %0, i64 %max.09
+  %spec.select7 = select i1 %cmp1, i64 %indvars.iv, i64 %idx.011
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond.not = icmp eq i64 %indvars.iv.next, %n
+  br i1 %exitcond.not, label %exit, label %for.body
+
+exit:
+  store i64 %spec.select, ptr %res_max
+  ret i64 %spec.select7
+}
+
+;
+; Check sge case.
+;
+define i64 @smax_idx_inverted_pred(ptr nocapture readonly %a, i64 %mm, i64 %ii, ptr nocapture writeonly %res_max, i64 %n) {
+; CHECK-LABEL: @smax_idx_inverted_pred(
+; CHECK-NOT:   vector.body:
+;
+entry:
+  br label %for.body
+
+for.body:
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %max.09 = phi i64 [ %mm, %entry ], [ %1, %for.body ]
+  %idx.011 = phi i64 [ %ii, %entry ], [ %spec.select7, %for.body ]
+  %arrayidx = getelementptr inbounds i64, ptr %a, i64 %indvars.iv
+  %0 = load i64, ptr %arrayidx
+  %1 = tail call i64 @llvm.smax.i64(i64 %max.09, i64 %0)
+  %cmp1 = icmp sge i64 %0, %max.09
+  %spec.select7 = select i1 %cmp1, i64 %indvars.iv, i64 %idx.011
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond.not = icmp eq i64 %indvars.iv.next, %n
+  br i1 %exitcond.not, label %exit, label %for.body
+
+exit:
+  store i64 %1, ptr %res_max
+  ret i64 %spec.select7
+}
+
+;
+; In such cases, the last index should be extracted.
+;
+define i64 @smax_idx_extract_last(ptr nocapture readonly %a, i64 %mm, i64 %ii, ptr nocapture writeonly %res_max, i64 %n) {
+; CHECK-LABEL: @smax_idx_extract_last(
+; CHECK-NOT:   vector.body:
+;
+entry:
+  br label %for.body
+
+for.body:
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %max.09 = phi i64 [ %mm, %entry ], [ %1, %for.body ]
+  %idx.011 = phi i64 [ %ii, %entry ], [ %spec.select7, %for.body ]
+  %arrayidx = getelementptr inbounds i64, ptr %a, i64 %indvars.iv
+  %0 = load i64, ptr %arrayidx
+  %1 = tail call i64 @llvm.smax.i64(i64 %max.09, i64 %0)
+  %cmp1.not = icmp sgt i64 %max.09, %0
+  %spec.select7 = select i1 %cmp1.not, i64 %idx.011, i64 %indvars.iv
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond.not = icmp eq i64 %indvars.iv.next, %n
+  br i1 %exitcond.not, label %exit, label %for.body
+
+exit:
+  store i64 %1, ptr %res_max
+  ret i64 %spec.select7
+}
+
+;
+; The operands of smax intrinsic and icmp are not the same to be recognized as MMI.
+;
+define i64 @smax_idx_not_vec_1(ptr nocapture readonly %a, ptr nocapture readonly %b, i64 %mm, i64 %ii, ptr nocapture writeonly %res_max, i64 %n) {
+; CHECK-LABEL: @smax_idx_not_vec_1(
+; CHECK-NOT:   vector.body:
+;
+  entry:
+  br label %for.body
+
+for.body:
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %max.09 = phi i64 [ %mm, %entry ], [ %2, %for.body ]
+  %idx.011 = phi i64 [ %ii, %entry ], [ %spec.select7, %for.body ]
+  %arrayidx = getelementptr inbounds i64, ptr %a, i64 %indvars.iv
+  %0 = load i64, ptr %arrayidx
+  %arrayidx.01 = getelementptr inbounds i64, ptr %b, i64 %indvars.iv
+  %1 = load i64, ptr %arrayidx
+  %2 = tail call i64 @llvm.smax.i64(i64 %max.09, i64 %0)
+  %cmp1 = icmp slt i64 %max.09, %1
+  %spec.select7 = select i1 %cmp1, i64 %indvars.iv, i64 %idx.011
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond.not = icmp eq i64 %indvars.iv.next, %n
+  br i1 %exitcond.not, label %exit, label %for.body
+
+exit:
+  store i64 %2, ptr %res_max
+  ret i64 %spec.select7
+}
+
+;
+; It cannot be recognized as MMI when the operand of index select is not an induction variable.
+;
+define i64 @smax_idx_not_vec_2(ptr nocapture readonly %a, i64 %mm, i64 %ii, ptr nocapture writeonly %res_max, i64 %n) {
+; CHECK-LABEL: @smax_idx_not_vec_2(
+; CHECK-NOT:   vector.body:
+;
+entry:
+  br label %for.body
+
+for.body:
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %max.09 = phi i64 [ %mm, %entry ], [ %1, %for.body ]
+  %idx.011 = phi i64 [ %ii, %entry ], [ %spec.select7, %for.body ]
+  %arrayidx = getelementptr inbounds i64, ptr %a, i64 %indvars.iv
+  %0 = load i64, ptr %arrayidx
+  %1 = tail call i64 @llvm.smax.i64(i64 %max.09, i64 %0)
+  %cmp1 = icmp slt i64 %max.09, %0
+  %spec.select7 = select i1 %cmp1, i64 123, i64 %idx.011
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond.not = icmp eq i64 %indvars.iv.next, %n
+  br i1 %exitcond.not, label %exit, label %for.body
+
+exit:
+  store i64 %1, ptr %res_max
+  ret i64 %spec.select7
+}
+
+declare i64 @llvm.smax.i64(i64, i64)