[llvm] [LLVM][MLGO] Fix: Index correctly into features to get default inlining decision (PR #141453)

[via llvm-commits]

https://github.com/Jellytabby created https://github.com/llvm/llvm-project/pull/141453

Currently, `InlineCostFeatureIndex::NumberOfFeatures` results in an index in the middle of the feature vector, therefore not correctly setting the default inlining decision and overwriting another feature. `FeatureIndex::NumberOfFeatures` is the last index of the feature vector, where the default inlining decision gets appended to when enabled. 

>From 259f358f92e32253beb85b68cc3922c5b26ac728 Mon Sep 17 00:00:00 2001
From: Sophia Herrmann <sherrman at ethz.ch>
Date: Mon, 26 May 2025 13:14:18 +0900
Subject: [PATCH] [LLVM][MLGO] Fix: Index correctly into features to get
 default inlining decision

---
 llvm/lib/Analysis/MLInlineAdvisor.cpp              | 2 +-
 llvm/test/Transforms/Inline/ML/interactive-mode.ll | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/Analysis/MLInlineAdvisor.cpp b/llvm/lib/Analysis/MLInlineAdvisor.cpp
index b6c784b965f79..81a3bc94a6ad8 100644
--- a/llvm/lib/Analysis/MLInlineAdvisor.cpp
+++ b/llvm/lib/Analysis/MLInlineAdvisor.cpp
@@ -441,7 +441,7 @@ std::unique_ptr<InlineAdvice> MLInlineAdvisor::getAdviceImpl(CallBase &CB) {
   }
   // This one would have been set up to be right at the end.
   if (!InteractiveChannelBaseName.empty() && InteractiveIncludeDefault)
-    *ModelRunner->getTensor<int64_t>(InlineCostFeatureIndex::NumberOfFeatures) =
+    *ModelRunner->getTensor<int64_t>(FeatureIndex::NumberOfFeatures) =
         GetDefaultAdvice(CB);
   return getAdviceFromModel(CB, ORE);
 }
diff --git a/llvm/test/Transforms/Inline/ML/interactive-mode.ll b/llvm/test/Transforms/Inline/ML/interactive-mode.ll
index 00a64c6c34d07..0866d14c6ece7 100644
--- a/llvm/test/Transforms/Inline/ML/interactive-mode.ll
+++ b/llvm/test/Transforms/Inline/ML/interactive-mode.ll
@@ -23,6 +23,7 @@
 ; CHECK:      unsimplified_common_instructions: 5
 ; CHECK:      callee_users: 3
 ; CHECK-DEFAULT: inlining_default: 0
+; CHECK-DEFAULT: inlining_default: 1
 ; CHECK:      observation: 5
 ; CHECK-NOT:  observation: 6