[llvm] [PGO] Add `llvm.loop.estimated_trip_count` metadata (PR #148758)

[Joel E. Denny via llvm-commits]

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@@ -0,0 +1,45 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Instrumentation/PGOEstimateTripCounts.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Transforms/Utils/LoopUtils.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "pgo-estimate-trip-counts"
+
+static bool runOnLoop(Loop *L) {
+  bool MadeChange = false;
+  std::optional<unsigned> TC = getLoopEstimatedTripCount(
+      L, /*EstimatedLoopInvocationWeight=*/nullptr, /*DbgForInit=*/true);
+  MadeChange |= setLoopEstimatedTripCount(L, TC);
+  for (Loop *SL : *L)
+    MadeChange |= runOnLoop(SL);
+  return MadeChange;
+}
+
+PreservedAnalyses PGOEstimateTripCountsPass::run(Module &M,
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jdenny-ornl wrote:

In PR #152775, I went with the suggestion to [make it a function pass](https://github.com/llvm/llvm-project/pull/148758/files#r2246193446).

https://github.com/llvm/llvm-project/pull/148758