[llvm] [CodeGen] Add OffloadBlockUniformityAnalysis for offload PGO (PR #178417)

[Juan Manuel Martinez Caamaño via llvm-commits]

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@@ -0,0 +1,117 @@
+//===- OffloadBlockUniformity.cpp - Offload block uniformity info --------===//
+//
+// 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/CodeGen/OffloadBlockUniformity.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/Instruction.h"
+#include "llvm/IR/Metadata.h"
+#include "llvm/Support/raw_ostream.h"
+#include <optional>
+
+using namespace llvm;
+
+static std::optional<bool> getIRBlockUniformity(const BasicBlock &BB) {
+  const Instruction *TI = BB.getTerminator();
+  if (!TI)
+    return std::nullopt;
+
+  MDNode *MD = TI->getMetadata(OffloadBlockUniformityInfo::MetadataName);
+  if (!MD)
+    return std::nullopt;
+
+  // Metadata format: !{i1 IsUniform} - structural validity assumed (verifier).
+  return mdconst::extract<ConstantInt>(MD->getOperand(0))->isOne();
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jmmartinez wrote:

We currently can represent 3 states: with-metadata uniform, with-metadata divergent and without-metadata (interpreted as divergent).

I'm not against this, but have you thought about not attaching metadata at all when divergent? Then we would only attach metadata for unform branches.

https://github.com/llvm/llvm-project/pull/178417