[Guards] Introduce loop-predication pass

This patch introduces guard based loop predication optimization. The new LoopPredication pass tries to convert loop variant range checks to loop invariant by widening checks across loop iterations. For example, it will convert

  for (i = 0; i < n; i++) {
    guard(i < len);
    ...
  }

to

  for (i = 0; i < n; i++) {
    guard(n - 1 < len);
    ...
  }

After this transformation the condition of the guard is loop invariant, so loop-unswitch can later unswitch the loop by this condition which basically predicates the loop by the widened condition:

  if (n - 1 < len)
    for (i = 0; i < n; i++) {
      ...
    } 
  else
    deoptimize

This patch relies on an NFC change to make ScalarEvolution::isMonotonicPredicate public (revision 293062).

Reviewed By: sanjoy

Differential Revision: https://reviews.llvm.org/D29034

llvm-svn: 293064

3 files changed, 796 insertions, 0 deletions

diff --git a/llvm/test/Transforms/LoopPredication/basic.ll b/llvm/test/Transforms/LoopPredication/basic.ll
new file mode 100644
index 00000000000..a347e6192bd
--- /dev/null
+++ b/llvm/test/Transforms/LoopPredication/basic.ll
@@ -0,0 +1,496 @@
+; RUN: opt -S -loop-predication < %s 2>&1 | FileCheck %s
+; RUN: opt -S -passes='require<scalar-evolution>,loop(loop-predication)' < %s 2>&1 | FileCheck %s
+
+declare void @llvm.experimental.guard(i1, ...)
+
+define i32 @unsigned_loop_0_to_n_ult_check(i32* %array, i32 %length, i32 %n) {
+; CHECK-LABEL: @unsigned_loop_0_to_n_ult_check
+entry:
+  %tmp5 = icmp eq i32 %n, 0
+  br i1 %tmp5, label %exit, label %loop.preheader
+
+loop.preheader:
+; CHECK: loop.preheader:
+; CHECK: [[max_index:[^ ]+]] = add i32 %n, -1
+; CHECK-NEXT: [[wide_cond:[^ ]+]] = icmp ult i32 [[max_index]], %length
+; CHECK-NEXT: br label %loop
+  br label %loop
+
+loop:
+; CHECK: loop:
+; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 [[wide_cond]], i32 9) [ "deopt"() ]
+  %loop.acc = phi i32 [ %loop.acc.next, %loop ], [ 0, %loop.preheader ]
+  %i = phi i32 [ %i.next, %loop ], [ 0, %loop.preheader ]
+  %within.bounds = icmp ult i32 %i, %length
+  call void (i1, ...) @llvm.experimental.guard(i1 %within.bounds, i32 9) [ "deopt"() ]
+
+  %i.i64 = zext i32 %i to i64
+  %array.i.ptr = getelementptr inbounds i32, i32* %array, i64 %i.i64
+  %array.i = load i32, i32* %array.i.ptr, align 4
+  %loop.acc.next = add i32 %loop.acc, %array.i
+
+  %i.next = add nuw i32 %i, 1
+  %continue = icmp ult i32 %i.next, %n
+  br i1 %continue, label %loop, label %exit
+
+exit:
+  %result = phi i32 [ 0, %entry ], [ %loop.acc.next, %loop ]
+  ret i32 %result
+}
+
+define i32 @unsigned_loop_0_to_n_ugt_check(i32* %array, i32 %length, i32 %n) {
+; CHECK-LABEL: @unsigned_loop_0_to_n_ugt_check
+entry:
+  %tmp5 = icmp eq i32 %n, 0
+  br i1 %tmp5, label %exit, label %loop.preheader
+
+loop.preheader:
+; CHECK: loop.preheader:
+; CHECK: [[max_index:[^ ]+]] = add i32 %n, -1
+; CHECK-NEXT: [[wide_cond:[^ ]+]] = icmp ult i32 [[max_index]], %length
+; CHECK-NEXT: br label %loop
+  br label %loop
+
+loop:
+; CHECK: loop:
+; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 [[wide_cond]], i32 9) [ "deopt"() ]
+  %loop.acc = phi i32 [ %loop.acc.next, %loop ], [ 0, %loop.preheader ]
+  %i = phi i32 [ %i.next, %loop ], [ 0, %loop.preheader ]
+  %within.bounds = icmp ugt i32 %length, %i
+  call void (i1, ...) @llvm.experimental.guard(i1 %within.bounds, i32 9) [ "deopt"() ]
+
+  %i.i64 = zext i32 %i to i64
+  %array.i.ptr = getelementptr inbounds i32, i32* %array, i64 %i.i64
+  %array.i = load i32, i32* %array.i.ptr, align 4
+  %loop.acc.next = add i32 %loop.acc, %array.i
+
+  %i.next = add nuw i32 %i, 1
+  %continue = icmp ult i32 %i.next, %n
+  br i1 %continue, label %loop, label %exit
+
+exit:
+  %result = phi i32 [ 0, %entry ], [ %loop.acc.next, %loop ]
+  ret i32 %result
+}
+
+
+define i32 @two_range_checks(i32* %array.1, i32 %length.1,
+                             i32* %array.2, i32 %length.2, i32 %n) {
+; CHECK-LABEL: @two_range_checks
+entry:
+  %tmp5 = icmp eq i32 %n, 0
+  br i1 %tmp5, label %exit, label %loop.preheader
+
+loop.preheader:
+; CHECK: loop.preheader:
+; CHECK: [[max_index:[^ ]+]] = add i32 %n, -1
+; CHECK-NEXT: [[wide_cond_1:[^ ]+]] = icmp ult i32 [[max_index]], %length.{{1|2}}
+; CHECK-NEXT: [[wide_cond_2:[^ ]+]] = icmp ult i32 [[max_index]], %length.{{1|2}}
+; CHECK-NEXT: br label %loop
+  br label %loop
+
+loop:
+; CHECK: loop:
+; CHECK: [[wide_cond:[^ ]+]] = and i1 [[wide_cond_1]], [[wide_cond_2]]
+; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 [[wide_cond]], i32 9) [ "deopt"() ]
+  %loop.acc = phi i32 [ %loop.acc.next, %loop ], [ 0, %loop.preheader ]
+  %i = phi i32 [ %i.next, %loop ], [ 0, %loop.preheader ]
+  %within.bounds.1 = icmp ult i32 %i, %length.1
+  %within.bounds.2 = icmp ult i32 %i, %length.2
+  %within.bounds = and i1 %within.bounds.1, %within.bounds.2
+  call void (i1, ...) @llvm.experimental.guard(i1 %within.bounds, i32 9) [ "deopt"() ]
+
+  %i.i64 = zext i32 %i to i64
+  %array.1.i.ptr = getelementptr inbounds i32, i32* %array.1, i64 %i.i64
+  %array.1.i = load i32, i32* %array.1.i.ptr, align 4
+  %loop.acc.1 = add i32 %loop.acc, %array.1.i
+
+  %array.2.i.ptr = getelementptr inbounds i32, i32* %array.2, i64 %i.i64
+  %array.2.i = load i32, i32* %array.2.i.ptr, align 4
+  %loop.acc.next = add i32 %loop.acc.1, %array.2.i
+
+  %i.next = add nuw i32 %i, 1
+  %continue = icmp ult i32 %i.next, %n
+  br i1 %continue, label %loop, label %exit
+
+exit:
+  %result = phi i32 [ 0, %entry ], [ %loop.acc.next, %loop ]
+  ret i32 %result
+}
+
+define i32 @three_range_checks(i32* %array.1, i32 %length.1,
+                               i32* %array.2, i32 %length.2,
+                               i32* %array.3, i32 %length.3, i32 %n) {
+; CHECK-LABEL: @three_range_checks
+entry:
+  %tmp5 = icmp eq i32 %n, 0
+  br i1 %tmp5, label %exit, label %loop.preheader
+
+loop.preheader:
+; CHECK: loop.preheader:
+; CHECK: [[max_index:[^ ]+]] = add i32 %n, -1
+; CHECK-NEXT: [[wide_cond_1:[^ ]+]] = icmp ult i32 [[max_index]], %length.{{1|2|3}}
+; CHECK-NEXT: [[wide_cond_2:[^ ]+]] = icmp ult i32 [[max_index]], %length.{{1|2|3}}
+; CHECK-NEXT: [[wide_cond_3:[^ ]+]] = icmp ult i32 [[max_index]], %length.{{1|2|3}}
+; CHECK-NEXT: br label %loop
+  br label %loop
+
+loop:
+; CHECK: loop:
+; CHECK: [[wide_cond_and:[^ ]+]] = and i1 [[wide_cond_1]], [[wide_cond_2]]
+; CHECK-NEXT: [[wide_cond:[^ ]+]] = and i1 [[wide_cond_and]], [[wide_cond_3]]
+; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 [[wide_cond]], i32 9) [ "deopt"() ]
+  %loop.acc = phi i32 [ %loop.acc.next, %loop ], [ 0, %loop.preheader ]
+  %i = phi i32 [ %i.next, %loop ], [ 0, %loop.preheader ]
+  %within.bounds.1 = icmp ult i32 %i, %length.1
+  %within.bounds.2 = icmp ult i32 %i, %length.2
+  %within.bounds.3 = icmp ult i32 %i, %length.3
+  %within.bounds.1.and.2 = and i1 %within.bounds.1, %within.bounds.2
+  %within.bounds = and i1 %within.bounds.1.and.2, %within.bounds.3
+  call void (i1, ...) @llvm.experimental.guard(i1 %within.bounds, i32 9) [ "deopt"() ]
+
+  %i.i64 = zext i32 %i to i64
+  %array.1.i.ptr = getelementptr inbounds i32, i32* %array.1, i64 %i.i64
+  %array.1.i = load i32, i32* %array.1.i.ptr, align 4
+  %loop.acc.1 = add i32 %loop.acc, %array.1.i
+
+  %array.2.i.ptr = getelementptr inbounds i32, i32* %array.2, i64 %i.i64
+  %array.2.i = load i32, i32* %array.2.i.ptr, align 4
+  %loop.acc.2 = add i32 %loop.acc.1, %array.2.i
+
+  %array.3.i.ptr = getelementptr inbounds i32, i32* %array.3, i64 %i.i64
+  %array.3.i = load i32, i32* %array.3.i.ptr, align 4
+  %loop.acc.next = add i32 %loop.acc.2, %array.3.i
+
+  %i.next = add nuw i32 %i, 1
+  %continue = icmp ult i32 %i.next, %n
+  br i1 %continue, label %loop, label %exit
+
+exit:
+  %result = phi i32 [ 0, %entry ], [ %loop.acc.next, %loop ]
+  ret i32 %result
+}
+
+define i32 @three_guards(i32* %array.1, i32 %length.1,
+                         i32* %array.2, i32 %length.2,
+                         i32* %array.3, i32 %length.3, i32 %n) {
+; CHECK-LABEL: @three_guards
+entry:
+  %tmp5 = icmp eq i32 %n, 0
+  br i1 %tmp5, label %exit, label %loop.preheader
+
+loop.preheader:
+; CHECK: loop.preheader:
+; CHECK: [[max_index:[^ ]+]] = add i32 %n, -1
+; CHECK-NEXT: [[wide_cond_1:[^ ]+]] = icmp ult i32 [[max_index]], %length.1
+; CHECK-NEXT: [[wide_cond_2:[^ ]+]] = icmp ult i32 [[max_index]], %length.2
+; CHECK-NEXT: [[wide_cond_3:[^ ]+]] = icmp ult i32 [[max_index]], %length.3
+; CHECK-NEXT: br label %loop
+  br label %loop
+
+loop:
+; CHECK: loop:
+; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 [[wide_cond_1]], i32 9) [ "deopt"() ]
+; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 [[wide_cond_2]], i32 9) [ "deopt"() ]
+; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 [[wide_cond_3]], i32 9) [ "deopt"() ]
+
+  %loop.acc = phi i32 [ %loop.acc.next, %loop ], [ 0, %loop.preheader ]
+  %i = phi i32 [ %i.next, %loop ], [ 0, %loop.preheader ]
+
+  %within.bounds.1 = icmp ult i32 %i, %length.1
+  call void (i1, ...) @llvm.experimental.guard(i1 %within.bounds.1, i32 9) [ "deopt"() ]
+
+  %i.i64 = zext i32 %i to i64
+  %array.1.i.ptr = getelementptr inbounds i32, i32* %array.1, i64 %i.i64
+  %array.1.i = load i32, i32* %array.1.i.ptr, align 4
+  %loop.acc.1 = add i32 %loop.acc, %array.1.i
+
+  %within.bounds.2 = icmp ult i32 %i, %length.2
+  call void (i1, ...) @llvm.experimental.guard(i1 %within.bounds.2, i32 9) [ "deopt"() ]
+
+  %array.2.i.ptr = getelementptr inbounds i32, i32* %array.2, i64 %i.i64
+  %array.2.i = load i32, i32* %array.2.i.ptr, align 4
+  %loop.acc.2 = add i32 %loop.acc.1, %array.2.i
+
+  %within.bounds.3 = icmp ult i32 %i, %length.3
+  call void (i1, ...) @llvm.experimental.guard(i1 %within.bounds.3, i32 9) [ "deopt"() ]
+
+  %array.3.i.ptr = getelementptr inbounds i32, i32* %array.3, i64 %i.i64
+  %array.3.i = load i32, i32* %array.3.i.ptr, align 4
+  %loop.acc.next = add i32 %loop.acc.2, %array.3.i
+
+  %i.next = add nuw i32 %i, 1
+  %continue = icmp ult i32 %i.next, %n
+  br i1 %continue, label %loop, label %exit
+
+exit:
+  %result = phi i32 [ 0, %entry ], [ %loop.acc.next, %loop ]
+  ret i32 %result
+}
+
+define i32 @signed_loop_start_to_n_sge_0_check(i32* %array, i32 %length, i32 %start, i32 %n) {
+; CHECK-LABEL: @signed_loop_start_to_n_sge_0_check
+entry:
+  %tmp5 = icmp eq i32 %n, 0
+  br i1 %tmp5, label %exit, label %loop.preheader
+
+loop.preheader:
+; CHECK: loop.preheader:
+; CHECK-NEXT: [[wide_cond:[^ ]+]] = icmp sge i32 %start, 0
+; CHECK-NEXT: br label %loop
+  br label %loop
+
+loop:
+; CHECK: loop:
+; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 [[wide_cond]], i32 9) [ "deopt"() ]
+  %loop.acc = phi i32 [ %loop.acc.next, %loop ], [ 0, %loop.preheader ]
+  %i = phi i32 [ %i.next, %loop ], [ %start, %loop.preheader ]
+  %within.bounds = icmp sge i32 %i, 0
+  call void (i1, ...) @llvm.experimental.guard(i1 %within.bounds, i32 9) [ "deopt"() ]
+
+  %i.i64 = zext i32 %i to i64
+  %array.i.ptr = getelementptr inbounds i32, i32* %array, i64 %i.i64
+  %array.i = load i32, i32* %array.i.ptr, align 4
+  %loop.acc.next = add i32 %loop.acc, %array.i
+
+  %i.next = add nsw i32 %i, 1
+  %continue = icmp slt i32 %i.next, %n
+  br i1 %continue, label %loop, label %exit
+
+exit:
+  %result = phi i32 [ 0, %entry ], [ %loop.acc.next, %loop ]
+  ret i32 %result
+}
+
+define i32 @signed_loop_start_to_n_upper_slt_length_check(i32* %array, i32 %length, i32 %start, i32 %n) {
+; CHECK-LABEL: @signed_loop_start_to_n_upper_slt_length_check
+entry:
+  %tmp5 = icmp sle i32 %n, 0
+  br i1 %tmp5, label %exit, label %loop.preheader
+
+loop.preheader:
+; CHECK: loop.preheader:
+; CHECK: [[start_1:[^ ]+]] = add i32 %start, 1
+; CHECK-NEXT: [[n_sgt_start_1:[^ ]+]] = icmp sgt i32 %n, [[start_1]]
+; CHECK-NEXT: [[smax:[^ ]+]] = select i1 [[n_sgt_start_1]], i32 %n, i32 [[start_1]]
+; CHECK-NEXT: [[max_index:[^ ]+]] = add i32 [[smax]], -1
+; CHECK-NEXT: [[wide_cond:[^ ]+]] = icmp slt i32 [[max_index]], %length
+; CHECK-NEXT: br label %loop
+  br label %loop
+
+loop:
+; CHECK: loop:
+; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 [[wide_cond]], i32 9) [ "deopt"() ]
+  %loop.acc = phi i32 [ %loop.acc.next, %loop ], [ 0, %loop.preheader ]
+  %i = phi i32 [ %i.next, %loop ], [ %start, %loop.preheader ]
+  %within.bounds = icmp slt i32 %i, %length
+  call void (i1, ...) @llvm.experimental.guard(i1 %within.bounds, i32 9) [ "deopt"() ]
+
+  %i.i64 = zext i32 %i to i64
+  %array.i.ptr = getelementptr inbounds i32, i32* %array, i64 %i.i64
+  %array.i = load i32, i32* %array.i.ptr, align 4
+  %loop.acc.next = add i32 %loop.acc, %array.i
+
+  %i.next = add nsw i32 %i, 1
+  %continue = icmp slt i32 %i.next, %n
+  br i1 %continue, label %loop, label %exit
+
+exit:
+  %result = phi i32 [ 0, %entry ], [ %loop.acc.next, %loop ]
+  ret i32 %result
+}
+
+define i32 @signed_loop_start_to_n_both_checks(i32* %array, i32 %length, i32 %start, i32 %n) {
+; CHECK-LABEL: @signed_loop_start_to_n_both_checks
+entry:
+  %tmp5 = icmp sle i32 %n, 0
+  br i1 %tmp5, label %exit, label %loop.preheader
+
+loop.preheader:
+; CHECK: loop.preheader:
+; CHECK: [[lower_check:[^ ]+]] = icmp sge i32 %start, 0
+; CHECK-NEXT: [[start_1:[^ ]+]] = add i32 %start, 1
+; CHECK-NEXT: [[n_sgt_start_1:[^ ]+]] = icmp sgt i32 %n, [[start_1]]
+; CHECK-NEXT: [[smax:[^ ]+]] = select i1 [[n_sgt_start_1]], i32 %n, i32 [[start_1]]
+; CHECK-NEXT: [[max_index:[^ ]+]] = add i32 [[smax]], -1
+; CHECK-NEXT: [[upper_check:[^ ]+]] = icmp slt i32 [[max_index]], %length
+; CHECK-NEXT: br label %loop
+  br label %loop
+
+loop:
+; CHECK: loop:
+; CHECK: [[wide_cond:[^ ]+]] = and i1 [[lower_check]], [[upper_check]]
+; CHECK-NEXT: call void (i1, ...) @llvm.experimental.guard(i1 [[wide_cond]], i32 9) [ "deopt"() ]
+  %loop.acc = phi i32 [ %loop.acc.next, %loop ], [ 0, %loop.preheader ]
+  %i = phi i32 [ %i.next, %loop ], [ %start, %loop.preheader ]
+  %within.bounds.1 = icmp slt i32 %i, %length
+  %within.bounds.2 = icmp sge i32 %i, 0
+  %within.bounds = and i1 %within.bounds.1, %within.bounds.2
+  call void (i1, ...) @llvm.experimental.guard(i1 %within.bounds, i32 9) [ "deopt"() ]
+
+  %i.i64 = zext i32 %i to i64
+  %array.i.ptr = getelementptr inbounds i32, i32* %array, i64 %i.i64
+  %array.i = load i32, i32* %array.i.ptr, align 4
+  %loop.acc.next = add i32 %loop.acc, %array.i
+
+  %i.next = add nsw i32 %i, 1
+  %continue = icmp slt i32 %i.next, %n
+  br i1 %continue, label %loop, label %exit
+
+exit:
+  %result = phi i32 [ 0, %entry ], [ %loop.acc.next, %loop ]
+  ret i32 %result
+}
+
+define i32 @unsigned_loop_0_to_n_unrelated_condition(i32* %array, i32 %length, i32 %n, i32 %x) {
+; CHECK-LABEL: @unsigned_loop_0_to_n_unrelated_condition
+entry:
+  %tmp5 = icmp eq i32 %n, 0
+  br i1 %tmp5, label %exit, label %loop.preheader
+
+loop.preheader:
+; CHECK: loop.preheader:
+; CHECK: [[max_index:[^ ]+]] = add i32 %n, -1
+; CHECK-NEXT: [[wide_cond:[^ ]+]] = icmp ult i32 [[max_index]], %length
+; CHECK-NEXT: br label %loop
+  br label %loop
+
+loop:
+; CHECK: loop:
+; CHECK: %unrelated.cond = icmp ult i32 %x, %length
+; CHECK: [[guard_cond:[^ ]+]] = and i1 %unrelated.cond, [[wide_cond]]
+; CHECK-NEXT: call void (i1, ...) @llvm.experimental.guard(i1 [[guard_cond]], i32 9) [ "deopt"() ]
+  %loop.acc = phi i32 [ %loop.acc.next, %loop ], [ 0, %loop.preheader ]
+  %i = phi i32 [ %i.next, %loop ], [ 0, %loop.preheader ]
+  %within.bounds = icmp ult i32 %i, %length
+  %unrelated.cond = icmp ult i32 %x, %length
+  %guard.cond = and i1 %within.bounds, %unrelated.cond
+  call void (i1, ...) @llvm.experimental.guard(i1 %guard.cond, i32 9) [ "deopt"() ]
+
+  %i.i64 = zext i32 %i to i64
+  %array.i.ptr = getelementptr inbounds i32, i32* %array, i64 %i.i64
+  %array.i = load i32, i32* %array.i.ptr, align 4
+  %loop.acc.next = add i32 %loop.acc, %array.i
+
+  %i.next = add nuw i32 %i, 1
+  %continue = icmp ult i32 %i.next, %n
+  br i1 %continue, label %loop, label %exit
+
+exit:
+  %result = phi i32 [ 0, %entry ], [ %loop.acc.next, %loop ]
+  ret i32 %result
+}
+
+; Don't change the guard condition if there were no widened subconditions
+define i32 @test_no_widened_conditions(i32* %array, i32 %length, i32 %n, i32 %x1, i32 %x2, i32 %x3) {
+; CHECK-LABEL: @test_no_widened_conditions
+entry:
+  %tmp5 = icmp eq i32 %n, 0
+  br i1 %tmp5, label %exit, label %loop.preheader
+
+loop.preheader:
+; CHECK: loop.preheader:
+; CHECK-NEXT: br label %loop
+  br label %loop
+
+loop:
+; CHECK: loop:
+; CHECK: %unrelated.cond.1 = icmp eq i32 %x1, %i
+; CHECK-NEXT: %unrelated.cond.2 = icmp eq i32 %x2, %i
+; CHECK-NEXT: %unrelated.cond.3 = icmp eq i32 %x3, %i
+; CHECK-NEXT: %unrelated.cond.and.1 = and i1 %unrelated.cond.1, %unrelated.cond.2
+; CHECK-NEXT: %guard.cond = and i1 %unrelated.cond.and.1, %unrelated.cond.3
+; CHECK-NEXT: call void (i1, ...) @llvm.experimental.guard(i1 %guard.cond, i32 9) [ "deopt"() ]
+  %loop.acc = phi i32 [ %loop.acc.next, %loop ], [ 0, %loop.preheader ]
+  %i = phi i32 [ %i.next, %loop ], [ 0, %loop.preheader ]
+  %unrelated.cond.1 = icmp eq i32 %x1, %i
+  %unrelated.cond.2 = icmp eq i32 %x2, %i
+  %unrelated.cond.3 = icmp eq i32 %x3, %i
+  %unrelated.cond.and.1 = and i1 %unrelated.cond.1, %unrelated.cond.2
+  %guard.cond = and i1 %unrelated.cond.and.1, %unrelated.cond.3
+
+  call void (i1, ...) @llvm.experimental.guard(i1 %guard.cond, i32 9) [ "deopt"() ]
+
+  %i.i64 = zext i32 %i to i64
+  %array.i.ptr = getelementptr inbounds i32, i32* %array, i64 %i.i64
+  %array.i = load i32, i32* %array.i.ptr, align 4
+  %loop.acc.next = add i32 %loop.acc, %array.i
+
+  %i.next = add nuw i32 %i, 1
+  %continue = icmp ult i32 %i.next, %n
+  br i1 %continue, label %loop, label %exit
+
+exit:
+  %result = phi i32 [ 0, %entry ], [ %loop.acc.next, %loop ]
+  ret i32 %result
+}
+
+define i32 @signed_loop_start_to_n_loop_variant_bound(i32* %array, i32 %x, i32 %start, i32 %n) {
+; CHECK-LABEL: @signed_loop_start_to_n_loop_variant_bound
+entry:
+  %tmp5 = icmp sle i32 %n, 0
+  br i1 %tmp5, label %exit, label %loop.preheader
+
+loop.preheader:
+; CHECK: loop.preheader:
+; CHECK-NEXT: br label %loop
+  br label %loop
+
+loop:
+; CHECK: loop:
+; CHECK: %bound = add i32 %i, %x
+; CHECK-NEXT: %within.bounds = icmp slt i32 %i, %bound
+; CHECK-NEXT: call void (i1, ...) @llvm.experimental.guard(i1 %within.bounds, i32 9) [ "deopt"() ]
+  %loop.acc = phi i32 [ %loop.acc.next, %loop ], [ 0, %loop.preheader ]
+  %i = phi i32 [ %i.next, %loop ], [ %start, %loop.preheader ]
+  %bound = add i32 %i, %x
+  %within.bounds = icmp slt i32 %i, %bound
+  call void (i1, ...) @llvm.experimental.guard(i1 %within.bounds, i32 9) [ "deopt"() ]
+
+  %i.i64 = zext i32 %i to i64
+  %array.i.ptr = getelementptr inbounds i32, i32* %array, i64 %i.i64
+  %array.i = load i32, i32* %array.i.ptr, align 4
+  %loop.acc.next = add i32 %loop.acc, %array.i
+
+  %i.next = add nsw i32 %i, 1
+  %continue = icmp slt i32 %i.next, %n
+  br i1 %continue, label %loop, label %exit
+
+exit:
+  %result = phi i32 [ 0, %entry ], [ %loop.acc.next, %loop ]
+  ret i32 %result
+}
+
+define i32 @signed_loop_start_to_n_non_monotonic_predicate(i32* %array, i32 %x, i32 %start, i32 %n) {
+; CHECK-LABEL: @signed_loop_start_to_n_non_monotonic_predicate
+entry:
+  %tmp5 = icmp sle i32 %n, 0
+  br i1 %tmp5, label %exit, label %loop.preheader
+
+loop.preheader:
+; CHECK: loop.preheader:
+; CHECK-NEXT: br label %loop
+  br label %loop
+
+loop:
+; CHECK: loop:
+; CHECK: %guard.cond = icmp eq i32 %i, %x
+; CHECK-NEXT: call void (i1, ...) @llvm.experimental.guard(i1 %guard.cond, i32 9) [ "deopt"() ]
+  %loop.acc = phi i32 [ %loop.acc.next, %loop ], [ 0, %loop.preheader ]
+  %i = phi i32 [ %i.next, %loop ], [ %start, %loop.preheader ]
+  %guard.cond = icmp eq i32 %i, %x
+  call void (i1, ...) @llvm.experimental.guard(i1 %guard.cond, i32 9) [ "deopt"() ]
+
+  %i.i64 = zext i32 %i to i64
+  %array.i.ptr = getelementptr inbounds i32, i32* %array, i64 %i.i64
+  %array.i = load i32, i32* %array.i.ptr, align 4
+  %loop.acc.next = add i32 %loop.acc, %array.i
+
+  %i.next = add nsw i32 %i, 1
+  %continue = icmp slt i32 %i.next, %n
+  br i1 %continue, label %loop, label %exit
+
+exit:
+  %result = phi i32 [ 0, %entry ], [ %loop.acc.next, %loop ]
+  ret i32 %result
+}
\ No newline at end of file
diff --git a/llvm/test/Transforms/LoopPredication/nested.ll b/llvm/test/Transforms/LoopPredication/nested.ll
new file mode 100644
index 00000000000..6b40cde3e57
--- /dev/null
+++ b/llvm/test/Transforms/LoopPredication/nested.ll
@@ -0,0 +1,160 @@
+; RUN: opt -S -loop-predication < %s 2>&1 | FileCheck %s
+; RUN: opt -S -passes='require<scalar-evolution>,loop(loop-predication)' < %s 2>&1 | FileCheck %s
+
+declare void @llvm.experimental.guard(i1, ...)
+
+define i32 @signed_loop_0_to_n_nested_0_to_l_inner_index_check(i32* %array, i32 %length, i32 %n, i32 %l) {
+; CHECK-LABEL: @signed_loop_0_to_n_nested_0_to_l_inner_index_check
+entry:
+  %tmp5 = icmp sle i32 %n, 0
+  br i1 %tmp5, label %exit, label %outer.loop.preheader
+
+outer.loop.preheader:
+; CHECK: outer.loop.preheader:
+; CHECK: [[iteration_count:[^ ]+]] = add i32 %l, -1
+  br label %outer.loop
+
+outer.loop:
+  %outer.loop.acc = phi i32 [ %outer.loop.acc.next, %outer.loop.inc ], [ 0, %outer.loop.preheader ]
+  %i = phi i32 [ %i.next, %outer.loop.inc ], [ 0, %outer.loop.preheader ]
+  %tmp6 = icmp sle i32 %l, 0
+  br i1 %tmp6, label %outer.loop.inc, label %inner.loop.preheader
+  
+inner.loop.preheader:
+; CHECK: inner.loop.preheader:
+; CHECK: [[wide_cond:[^ ]+]] = icmp slt i32 [[iteration_count]], %length
+  br label %inner.loop
+
+inner.loop:
+; CHECK: inner.loop:
+; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 [[wide_cond]], i32 9) [ "deopt"() ]
+  %inner.loop.acc = phi i32 [ %inner.loop.acc.next, %inner.loop ], [ %outer.loop.acc, %inner.loop.preheader ]
+  %j = phi i32 [ %j.next, %inner.loop ], [ 0, %inner.loop.preheader ]
+
+  %within.bounds = icmp slt i32 %j, %length
+  call void (i1, ...) @llvm.experimental.guard(i1 %within.bounds, i32 9) [ "deopt"() ]
+  
+  %j.i64 = zext i32 %j to i64
+  %array.j.ptr = getelementptr inbounds i32, i32* %array, i64 %j.i64
+  %array.j = load i32, i32* %array.j.ptr, align 4
+  %inner.loop.acc.next = add i32 %inner.loop.acc, %array.j
+
+  %j.next = add nsw i32 %j, 1
+  %inner.continue = icmp slt i32 %j.next, %l
+  br i1 %inner.continue, label %inner.loop, label %outer.loop.inc
+
+outer.loop.inc:
+  %outer.loop.acc.next = phi i32 [ %inner.loop.acc.next, %inner.loop ], [ %outer.loop.acc, %outer.loop ]
+  %i.next = add nsw i32 %i, 1
+  %outer.continue = icmp slt i32 %i.next, %n
+  br i1 %outer.continue, label %outer.loop, label %exit
+
+exit:
+  %result = phi i32 [ 0, %entry ], [ %outer.loop.acc.next, %outer.loop.inc ]
+  ret i32 %result
+}
+
+define i32 @signed_loop_0_to_n_nested_0_to_l_outer_index_check(i32* %array, i32 %length, i32 %n, i32 %l) {
+; CHECK-LABEL: @signed_loop_0_to_n_nested_0_to_l_outer_index_check
+entry:
+  %tmp5 = icmp sle i32 %n, 0
+  br i1 %tmp5, label %exit, label %outer.loop.preheader
+
+outer.loop.preheader:
+; CHECK: outer.loop.preheader:
+; CHECK: [[iteration_count:[^ ]+]] = add i32 %n, -1
+; CHECK: [[wide_cond:[^ ]+]] = icmp slt i32 [[iteration_count]], %length
+  br label %outer.loop
+
+outer.loop:
+  %outer.loop.acc = phi i32 [ %outer.loop.acc.next, %outer.loop.inc ], [ 0, %outer.loop.preheader ]
+  %i = phi i32 [ %i.next, %outer.loop.inc ], [ 0, %outer.loop.preheader ]
+  %tmp6 = icmp sle i32 %l, 0
+  br i1 %tmp6, label %outer.loop.inc, label %inner.loop.preheader
+  
+inner.loop.preheader:
+  br label %inner.loop
+
+inner.loop:
+; CHECK: inner.loop:
+; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 [[wide_cond]], i32 9) [ "deopt"() ]
+
+  %inner.loop.acc = phi i32 [ %inner.loop.acc.next, %inner.loop ], [ %outer.loop.acc, %inner.loop.preheader ]
+  %j = phi i32 [ %j.next, %inner.loop ], [ 0, %inner.loop.preheader ]
+
+  %within.bounds = icmp slt i32 %i, %length
+  call void (i1, ...) @llvm.experimental.guard(i1 %within.bounds, i32 9) [ "deopt"() ]
+  
+  %i.i64 = zext i32 %i to i64
+  %array.i.ptr = getelementptr inbounds i32, i32* %array, i64 %i.i64
+  %array.i = load i32, i32* %array.i.ptr, align 4
+  %inner.loop.acc.next = add i32 %inner.loop.acc, %array.i
+
+  %j.next = add nsw i32 %j, 1
+  %inner.continue = icmp slt i32 %j.next, %l
+  br i1 %inner.continue, label %inner.loop, label %outer.loop.inc
+
+outer.loop.inc:
+  %outer.loop.acc.next = phi i32 [ %inner.loop.acc.next, %inner.loop ], [ %outer.loop.acc, %outer.loop ]
+  %i.next = add nsw i32 %i, 1
+  %outer.continue = icmp slt i32 %i.next, %n
+  br i1 %outer.continue, label %outer.loop, label %exit
+
+exit:
+  %result = phi i32 [ 0, %entry ], [ %outer.loop.acc.next, %outer.loop.inc ]
+  ret i32 %result
+}
+
+define i32 @signed_loop_0_to_n_nested_i_to_l_inner_index_check(i32* %array, i32 %length, i32 %n, i32 %l) {
+; CHECK-LABEL: @signed_loop_0_to_n_nested_i_to_l_inner_index_check
+entry:
+  %tmp5 = icmp sle i32 %n, 0
+  br i1 %tmp5, label %exit, label %outer.loop.preheader
+
+outer.loop.preheader:
+  br label %outer.loop
+
+outer.loop:
+; CHECK: outer.loop:
+; CHECK: [[i_1:[^ ]+]] = add i32 %i, 1
+; CHECK-NEXT: [[l_sgt_i_1:[^ ]+]] = icmp sgt i32 %l, [[i_1]]
+; CHECK-NEXT: [[smax:[^ ]+]] = select i1 [[l_sgt_i_1]], i32 %l, i32 [[i_1]]
+; CHECK-NEXT: [[max_j:[^ ]+]] = add i32 [[smax]], -1
+  %outer.loop.acc = phi i32 [ %outer.loop.acc.next, %outer.loop.inc ], [ 0, %outer.loop.preheader ]
+  %i = phi i32 [ %i.next, %outer.loop.inc ], [ 0, %outer.loop.preheader ]
+  %tmp6 = icmp sle i32 %l, 0
+  br i1 %tmp6, label %outer.loop.inc, label %inner.loop.preheader
+  
+inner.loop.preheader:
+; CHECK: inner.loop.preheader:
+; CHECK: [[wide_cond:[^ ]+]] = icmp slt i32 [[max_j]], %length
+  br label %inner.loop
+
+inner.loop:
+; CHECK: inner.loop:
+; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 [[wide_cond]], i32 9) [ "deopt"() ]
+  %inner.loop.acc = phi i32 [ %inner.loop.acc.next, %inner.loop ], [ %outer.loop.acc, %inner.loop.preheader ]
+  %j = phi i32 [ %j.next, %inner.loop ], [ %i, %inner.loop.preheader ]
+
+  %within.bounds = icmp slt i32 %j, %length
+  call void (i1, ...) @llvm.experimental.guard(i1 %within.bounds, i32 9) [ "deopt"() ]
+  
+  %j.i64 = zext i32 %j to i64
+  %array.j.ptr = getelementptr inbounds i32, i32* %array, i64 %j.i64
+  %array.j = load i32, i32* %array.j.ptr, align 4
+  %inner.loop.acc.next = add i32 %inner.loop.acc, %array.j
+
+  %j.next = add nsw i32 %j, 1
+  %inner.continue = icmp slt i32 %j.next, %l
+  br i1 %inner.continue, label %inner.loop, label %outer.loop.inc
+
+outer.loop.inc:
+  %outer.loop.acc.next = phi i32 [ %inner.loop.acc.next, %inner.loop ], [ %outer.loop.acc, %outer.loop ]
+  %i.next = add nsw i32 %i, 1
+  %outer.continue = icmp slt i32 %i.next, %n
+  br i1 %outer.continue, label %outer.loop, label %exit
+
+exit:
+  %result = phi i32 [ 0, %entry ], [ %outer.loop.acc.next, %outer.loop.inc ]
+  ret i32 %result
+}
\ No newline at end of file
diff --git a/llvm/test/Transforms/LoopPredication/visited.ll b/llvm/test/Transforms/LoopPredication/visited.ll
new file mode 100644
index 00000000000..e9aae77f8e6
--- /dev/null
+++ b/llvm/test/Transforms/LoopPredication/visited.ll
@@ -0,0 +1,140 @@
+; RUN: opt -S -loop-predication < %s 2>&1 | FileCheck %s
+; RUN: opt -S -passes='require<scalar-evolution>,loop(loop-predication)' < %s 2>&1 | FileCheck %s
+
+declare void @llvm.experimental.guard(i1, ...)
+
+define i32 @test_visited(i32* %array, i32 %length, i32 %n, i32 %x) {
+; CHECK-LABEL: @test_visited
+entry:
+  %tmp5 = icmp eq i32 %n, 0
+  br i1 %tmp5, label %exit, label %loop.preheader
+
+loop.preheader:
+; CHECK: loop.preheader:
+; CHECK: [[iteration_count:[^ ]+]] = add i32 %n, -1
+; CHECK-NEXT: [[wide_cond:[^ ]+]] = icmp ult i32 [[iteration_count]], %length
+; CHECK-NEXT: br label %loop
+  br label %loop
+
+loop:
+; CHECK: loop:
+; CHECK: %unrelated.cond = icmp eq i32 %x, %i
+; CHECK: [[guard_cond:[^ ]+]] = and i1 %unrelated.cond, [[wide_cond]]
+; CHECK-NEXT: call void (i1, ...) @llvm.experimental.guard(i1 [[guard_cond]], i32 9) [ "deopt"() ]
+  %loop.acc = phi i32 [ %loop.acc.next, %loop ], [ 0, %loop.preheader ]
+  %i = phi i32 [ %i.next, %loop ], [ 0, %loop.preheader ]
+  %within.bounds = icmp ult i32 %i, %length
+  %unrelated.cond = icmp eq i32 %x, %i
+  %guard.cond.2 = and i1 %within.bounds, %unrelated.cond
+  %guard.cond.3 = and i1 %guard.cond.2, %unrelated.cond
+  %guard.cond.4 = and i1 %guard.cond.3, %guard.cond.2
+  %guard.cond.5 = and i1 %guard.cond.4, %guard.cond.3
+  %guard.cond.6 = and i1 %guard.cond.5, %guard.cond.4
+  %guard.cond.7 = and i1 %guard.cond.6, %guard.cond.5
+  %guard.cond.8 = and i1 %guard.cond.7, %guard.cond.6
+  %guard.cond.9 = and i1 %guard.cond.8, %guard.cond.7
+  %guard.cond.10 = and i1 %guard.cond.9, %guard.cond.8
+  %guard.cond.11 = and i1 %guard.cond.10, %guard.cond.9
+  %guard.cond.12 = and i1 %guard.cond.11, %guard.cond.10
+  %guard.cond.13 = and i1 %guard.cond.12, %guard.cond.11
+  %guard.cond.14 = and i1 %guard.cond.13, %guard.cond.12
+  %guard.cond.15 = and i1 %guard.cond.14, %guard.cond.13
+  %guard.cond.16 = and i1 %guard.cond.15, %guard.cond.14
+  %guard.cond.17 = and i1 %guard.cond.16, %guard.cond.15
+  %guard.cond.18 = and i1 %guard.cond.17, %guard.cond.16
+  %guard.cond.19 = and i1 %guard.cond.18, %guard.cond.17
+  %guard.cond.20 = and i1 %guard.cond.19, %guard.cond.18
+  %guard.cond.21 = and i1 %guard.cond.20, %guard.cond.19
+  %guard.cond.22 = and i1 %guard.cond.21, %guard.cond.20
+  %guard.cond.23 = and i1 %guard.cond.22, %guard.cond.21
+  %guard.cond.24 = and i1 %guard.cond.23, %guard.cond.22
+  %guard.cond.25 = and i1 %guard.cond.24, %guard.cond.23
+  %guard.cond.26 = and i1 %guard.cond.25, %guard.cond.24
+  %guard.cond.27 = and i1 %guard.cond.26, %guard.cond.25
+  %guard.cond.28 = and i1 %guard.cond.27, %guard.cond.26
+  %guard.cond.29 = and i1 %guard.cond.28, %guard.cond.27
+  %guard.cond.30 = and i1 %guard.cond.29, %guard.cond.28
+  %guard.cond.31 = and i1 %guard.cond.30, %guard.cond.29
+  %guard.cond.32 = and i1 %guard.cond.31, %guard.cond.30
+  %guard.cond.33 = and i1 %guard.cond.32, %guard.cond.31
+  %guard.cond.34 = and i1 %guard.cond.33, %guard.cond.32
+  %guard.cond.35 = and i1 %guard.cond.34, %guard.cond.33
+  %guard.cond.36 = and i1 %guard.cond.35, %guard.cond.34
+  %guard.cond.37 = and i1 %guard.cond.36, %guard.cond.35
+  %guard.cond.38 = and i1 %guard.cond.37, %guard.cond.36
+  %guard.cond.39 = and i1 %guard.cond.38, %guard.cond.37
+  %guard.cond.40 = and i1 %guard.cond.39, %guard.cond.38
+  %guard.cond.41 = and i1 %guard.cond.40, %guard.cond.39
+  %guard.cond.42 = and i1 %guard.cond.41, %guard.cond.40
+  %guard.cond.43 = and i1 %guard.cond.42, %guard.cond.41
+  %guard.cond.44 = and i1 %guard.cond.43, %guard.cond.42
+  %guard.cond.45 = and i1 %guard.cond.44, %guard.cond.43
+  %guard.cond.46 = and i1 %guard.cond.45, %guard.cond.44
+  %guard.cond.47 = and i1 %guard.cond.46, %guard.cond.45
+  %guard.cond.48 = and i1 %guard.cond.47, %guard.cond.46
+  %guard.cond.49 = and i1 %guard.cond.48, %guard.cond.47
+  %guard.cond.50 = and i1 %guard.cond.49, %guard.cond.48
+  %guard.cond.51 = and i1 %guard.cond.50, %guard.cond.49
+  %guard.cond.52 = and i1 %guard.cond.51, %guard.cond.50
+  %guard.cond.53 = and i1 %guard.cond.52, %guard.cond.51
+  %guard.cond.54 = and i1 %guard.cond.53, %guard.cond.52
+  %guard.cond.55 = and i1 %guard.cond.54, %guard.cond.53
+  %guard.cond.56 = and i1 %guard.cond.55, %guard.cond.54
+  %guard.cond.57 = and i1 %guard.cond.56, %guard.cond.55
+  %guard.cond.58 = and i1 %guard.cond.57, %guard.cond.56
+  %guard.cond.59 = and i1 %guard.cond.58, %guard.cond.57
+  %guard.cond.60 = and i1 %guard.cond.59, %guard.cond.58
+  %guard.cond.61 = and i1 %guard.cond.60, %guard.cond.59
+  %guard.cond.62 = and i1 %guard.cond.61, %guard.cond.60
+  %guard.cond.63 = and i1 %guard.cond.62, %guard.cond.61
+  %guard.cond.64 = and i1 %guard.cond.63, %guard.cond.62
+  %guard.cond.65 = and i1 %guard.cond.64, %guard.cond.63
+  %guard.cond.66 = and i1 %guard.cond.65, %guard.cond.64
+  %guard.cond.67 = and i1 %guard.cond.66, %guard.cond.65
+  %guard.cond.68 = and i1 %guard.cond.67, %guard.cond.66
+  %guard.cond.69 = and i1 %guard.cond.68, %guard.cond.67
+  %guard.cond.70 = and i1 %guard.cond.69, %guard.cond.68
+  %guard.cond.71 = and i1 %guard.cond.70, %guard.cond.69
+  %guard.cond.72 = and i1 %guard.cond.71, %guard.cond.70
+  %guard.cond.73 = and i1 %guard.cond.72, %guard.cond.71
+  %guard.cond.74 = and i1 %guard.cond.73, %guard.cond.72
+  %guard.cond.75 = and i1 %guard.cond.74, %guard.cond.73
+  %guard.cond.76 = and i1 %guard.cond.75, %guard.cond.74
+  %guard.cond.77 = and i1 %guard.cond.76, %guard.cond.75
+  %guard.cond.78 = and i1 %guard.cond.77, %guard.cond.76
+  %guard.cond.79 = and i1 %guard.cond.78, %guard.cond.77
+  %guard.cond.80 = and i1 %guard.cond.79, %guard.cond.78
+  %guard.cond.81 = and i1 %guard.cond.80, %guard.cond.79
+  %guard.cond.82 = and i1 %guard.cond.81, %guard.cond.80
+  %guard.cond.83 = and i1 %guard.cond.82, %guard.cond.81
+  %guard.cond.84 = and i1 %guard.cond.83, %guard.cond.82
+  %guard.cond.85 = and i1 %guard.cond.84, %guard.cond.83
+  %guard.cond.86 = and i1 %guard.cond.85, %guard.cond.84
+  %guard.cond.87 = and i1 %guard.cond.86, %guard.cond.85
+  %guard.cond.88 = and i1 %guard.cond.87, %guard.cond.86
+  %guard.cond.89 = and i1 %guard.cond.88, %guard.cond.87
+  %guard.cond.90 = and i1 %guard.cond.89, %guard.cond.88
+  %guard.cond.91 = and i1 %guard.cond.90, %guard.cond.89
+  %guard.cond.92 = and i1 %guard.cond.91, %guard.cond.90
+  %guard.cond.93 = and i1 %guard.cond.92, %guard.cond.91
+  %guard.cond.94 = and i1 %guard.cond.93, %guard.cond.92
+  %guard.cond.95 = and i1 %guard.cond.94, %guard.cond.93
+  %guard.cond.96 = and i1 %guard.cond.95, %guard.cond.94
+  %guard.cond.97 = and i1 %guard.cond.96, %guard.cond.95
+  %guard.cond.98 = and i1 %guard.cond.97, %guard.cond.96
+  %guard.cond.99 = and i1 %guard.cond.98, %guard.cond.97
+  call void (i1, ...) @llvm.experimental.guard(i1 %guard.cond.99, i32 9) [ "deopt"() ]
+
+  %i.i64 = zext i32 %i to i64
+  %array.i.ptr = getelementptr inbounds i32, i32* %array, i64 %i.i64
+  %array.i = load i32, i32* %array.i.ptr, align 4
+  %loop.acc.next = add i32 %loop.acc, %array.i
+
+  %i.next = add nuw i32 %i, 1
+  %continue = icmp ult i32 %i.next, %n
+  br i1 %continue, label %loop, label %exit
+
+exit:
+  %result = phi i32 [ 0, %entry ], [ %loop.acc.next, %loop ]
+  ret i32 %result
+}
\ No newline at end of file