[llvm] [LoopUtils] prevent negative estimated trip count result (PR #195610)

[Joel E. Denny via llvm-commits]

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@@ -0,0 +1,33 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
+; RUN: opt -passes=loop-unroll -S < %s | FileCheck %s
+
+define void @PR173169() !prof !0 {
+; CHECK-LABEL: define void @PR173169(
+; CHECK-SAME: ) !prof [[PROF0:![0-9]+]] {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    br label %[[LOOP:.*]]
+; CHECK:       [[LOOP]]:
+; CHECK-NEXT:    br i1 true, label %[[LOOP]], label %[[EXIT:.*]], !llvm.loop [[LOOP1:![0-9]+]]
+; CHECK:       [[EXIT]]:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %loop
+
+loop:                                             ; preds = %loop, %entry
+  br i1 true, label %loop, label %exit, !llvm.loop !1
+
+exit:                                             ; preds = %loop
+  ret void
+}
+
+!0 = !{!"function_entry_count", i64 1000}
+!1 = distinct !{!1, !2, !3}
+!2 = !{!"llvm.loop.peeled.count", i32 1}
+!3 = !{!"llvm.loop.estimated_trip_count", i32 -1}
+;.
+; CHECK: [[PROF0]] = !{!"function_entry_count", i64 1000}
+; CHECK: [[LOOP1]] = distinct !{[[LOOP1]], [[META2:![0-9]+]], [[META3:![0-9]+]]}
+; CHECK: [[META2]] = !{!"llvm.loop.peeled.count", i32 1}
+; CHECK: [[META3]] = !{!"llvm.loop.estimated_trip_count", i32 -1}
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jdenny-ornl wrote:

Please add some comments somewhere in the test to clarify that estimated trip counts are not actually negative.  Please update the PR initial comment as well.

https://github.com/llvm/llvm-project/pull/195610