[llvm] [Transforms][Utils] Test for branch weight preservation in LoopSplitUtils (PR #213647)

[Ramkumar Ramachandra via llvm-commits]

================
@@ -0,0 +1,67 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
+; RUN: opt -passes=loop-split-utils -loop-split-points=50 -S < %s | FileCheck %s
+
+; The original latch carries branch weights; splitting must propagate them onto
+; each partition's clamped latch. The newly created partition guards have no
+; source profile, so in a profiled function they are marked with unknown
+; weights.
+
+define void @basic(ptr %a, i64 %n) !prof !0 {
+; CHECK-LABEL: define void @basic(
+; CHECK-SAME: ptr [[A:%.*]], i64 [[N:%.*]]) !prof [[PROF0:![0-9]+]] {
+; CHECK-NEXT:  [[LS_GUARD0:.*:]]
+; CHECK-NEXT:    [[SMAX:%.*]] = call i64 @llvm.smax.i64(i64 [[N]], i64 1)
+; CHECK-NEXT:    [[TMP0:%.*]] = add nsw i64 [[SMAX]], -1
+; CHECK-NEXT:    [[SMIN:%.*]] = call i64 @llvm.smin.i64(i64 [[TMP0]], i64 49)
+; CHECK-NEXT:    [[ITR_CHK:%.*]] = icmp sle i64 0, [[SMIN]]
+; CHECK-NEXT:    br i1 [[ITR_CHK]], label %[[ENTRY:.*]], label %[[LS_GUARD1:.*]], !prof [[PROF1:![0-9]+]]
+; CHECK:       [[ENTRY]]:
+; CHECK-NEXT:    br label %[[LOOP:.*]]
+; CHECK:       [[LOOP]]:
+; CHECK-NEXT:    [[I:%.*]] = phi i64 [ 0, %[[ENTRY]] ], [ [[I_NEXT:%.*]], %[[LOOP]] ]
+; CHECK-NEXT:    [[P:%.*]] = getelementptr i64, ptr [[A]], i64 [[I]]
+; CHECK-NEXT:    store i64 [[I]], ptr [[P]], align 4
+; CHECK-NEXT:    [[I_NEXT]] = add i64 [[I]], 1
+; CHECK-NEXT:    [[ITR_CHK1:%.*]] = icmp sle i64 [[I_NEXT]], [[SMIN]]
+; CHECK-NEXT:    br i1 [[ITR_CHK1]], label %[[LOOP]], label %[[EXIT:.*]], !prof [[PROF2:![0-9]+]]
+; CHECK:       [[EXIT]]:
+; CHECK-NEXT:    br label %[[LS_GUARD1]]
+; CHECK:       [[LS_GUARD1]]:
+; CHECK-NEXT:    [[ITR_CHK2:%.*]] = icmp sle i64 50, [[TMP0]]
+; CHECK-NEXT:    br i1 [[ITR_CHK2]], label %[[ENTRY_LS1:.*]], label %[[LS_FINAL_EXIT:.*]], !prof [[PROF1]]
+; CHECK:       [[ENTRY_LS1]]:
+; CHECK-NEXT:    br label %[[LOOP_LS1:.*]]
+; CHECK:       [[LOOP_LS1]]:
+; CHECK-NEXT:    [[I_LS1:%.*]] = phi i64 [ 50, %[[ENTRY_LS1]] ], [ [[I_NEXT_LS1:%.*]], %[[LOOP_LS1]] ]
+; CHECK-NEXT:    [[P_LS1:%.*]] = getelementptr i64, ptr [[A]], i64 [[I_LS1]]
+; CHECK-NEXT:    store i64 [[I_LS1]], ptr [[P_LS1]], align 4
+; CHECK-NEXT:    [[I_NEXT_LS1]] = add i64 [[I_LS1]], 1
+; CHECK-NEXT:    [[ITR_CHK3:%.*]] = icmp sle i64 [[I_NEXT_LS1]], [[TMP0]]
+; CHECK-NEXT:    br i1 [[ITR_CHK3]], label %[[LOOP_LS1]], label %[[LS_EXIT1:.*]], !prof [[PROF2]]
+; CHECK:       [[LS_EXIT1]]:
+; CHECK-NEXT:    br label %[[LS_FINAL_EXIT]]
+; CHECK:       [[LS_FINAL_EXIT]]:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %loop
+
+loop:
+  %i = phi i64 [ 0, %entry ], [ %i.next, %loop ]
+  %p = getelementptr i64, ptr %a, i64 %i
+  store i64 %i, ptr %p
+  %i.next = add i64 %i, 1
+  %c = icmp slt i64 %i.next, %n
----------------
artagnon wrote:

```suggestion
  %ec = icmp slt i64 %i.next, %n
```

For "exit condition".

https://github.com/llvm/llvm-project/pull/213647