[llvm] [mlgo][inliner] Fix incorrect state tracking when deferring to the default policy (PR #163477)

[Mircea Trofin via llvm-commits]

https://github.com/mtrofin updated https://github.com/llvm/llvm-project/pull/163477

>From 452c909bd5ab0addbc9b23dfffa3df84fba34b20 Mon Sep 17 00:00:00 2001
From: Mircea Trofin <mtrofin at google.com>
Date: Tue, 14 Oct 2025 17:05:41 -0700
Subject: [PATCH] [mlgo][inliner] Fix incorrect state tracking when deferring
 to the default policy

---
 llvm/lib/Analysis/MLInlineAdvisor.cpp         | 18 +++++-
 .../ML/state-accounting-skip-non-cold.ll      | 55 +++++++++++++++++++
 2 files changed, 70 insertions(+), 3 deletions(-)
 create mode 100644 llvm/test/Transforms/Inline/ML/state-accounting-skip-non-cold.ll

diff --git a/llvm/lib/Analysis/MLInlineAdvisor.cpp b/llvm/lib/Analysis/MLInlineAdvisor.cpp
index f90717d3085eb..1d1a5560be478 100644
--- a/llvm/lib/Analysis/MLInlineAdvisor.cpp
+++ b/llvm/lib/Analysis/MLInlineAdvisor.cpp
@@ -61,6 +61,9 @@ static cl::opt<SkipMLPolicyCriteria> SkipPolicy(
 static cl::opt<std::string> ModelSelector("ml-inliner-model-selector",
                                           cl::Hidden, cl::init(""));
 
+static cl::opt<bool> StopImmediatelyForTest("ml-inliner-stop-immediately",
+                                            cl::Hidden);
+
 #if defined(LLVM_HAVE_TF_AOT_INLINERSIZEMODEL)
 // codegen-ed file
 #include "InlinerSizeModel.h" // NOLINT
@@ -214,6 +217,7 @@ MLInlineAdvisor::MLInlineAdvisor(
     return;
   }
   ModelRunner->switchContext("");
+  ForceStop = StopImmediatelyForTest;
 }
 
 unsigned MLInlineAdvisor::getInitialFunctionLevel(const Function &F) const {
@@ -379,9 +383,17 @@ std::unique_ptr<InlineAdvice> MLInlineAdvisor::getAdviceImpl(CallBase &CB) {
   auto &ORE = FAM.getResult<OptimizationRemarkEmitterAnalysis>(Caller);
 
   if (SkipPolicy == SkipMLPolicyCriteria::IfCallerIsNotCold) {
-    if (!PSI.isFunctionEntryCold(&Caller))
-      return std::make_unique<InlineAdvice>(this, CB, ORE,
-                                            GetDefaultAdvice(CB));
+    if (!PSI.isFunctionEntryCold(&Caller)) {
+      // Return a MLInlineAdvice, despite delegating to the default advice,
+      // because we need to keep track of the internal state. This is different
+      // from the other instances where we return a "default" InlineAdvice,
+      // which happen at points we won't come back to the MLAdvisor for
+      // decisions requiring that state.
+      return ForceStop ? std::make_unique<InlineAdvice>(this, CB, ORE,
+                                                        GetDefaultAdvice(CB))
+                       : std::make_unique<MLInlineAdvice>(this, CB, ORE,
+                                                          GetDefaultAdvice(CB));
+    }
   }
   auto MandatoryKind = InlineAdvisor::getMandatoryKind(CB, FAM, ORE);
   // If this is a "never inline" case, there won't be any changes to internal
diff --git a/llvm/test/Transforms/Inline/ML/state-accounting-skip-non-cold.ll b/llvm/test/Transforms/Inline/ML/state-accounting-skip-non-cold.ll
new file mode 100644
index 0000000000000..0887f5e29187d
--- /dev/null
+++ b/llvm/test/Transforms/Inline/ML/state-accounting-skip-non-cold.ll
@@ -0,0 +1,55 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
+; REQUIRES: llvm_inliner_model_autogenerated && asserts
+; RUN: opt -passes='default<O3>' -enable-ml-inliner=release -ml-inliner-skip-policy=if-caller-not-cold -S %s -o - | FileCheck %s
+; RUN: opt -passes='default<O3>' -ml-inliner-stop-immediately -enable-ml-inliner=release -ml-inliner-skip-policy=if-caller-not-cold -S %s -o - | FileCheck %s
+
+declare ptr @f()
+
+define void @e() #0 {
+; CHECK-LABEL: define void @e(
+; CHECK-SAME: ) local_unnamed_addr #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT:    tail call void @d()
+; CHECK-NEXT:    tail call void @g()
+; CHECK-NEXT:    tail call void @d()
+; CHECK-NEXT:    tail call void @g()
+; CHECK-NEXT:    tail call void @d()
+; CHECK-NEXT:    tail call void @g()
+; CHECK-NEXT:    ret void
+;
+  call void @h()
+  call void @h()
+  call void @h()
+  ret void
+}
+
+define void @d() {
+; CHECK-LABEL: define void @d() local_unnamed_addr {
+; CHECK-NEXT:    tail call void @f()
+; CHECK-NEXT:    ret void
+;
+  call void @f()
+  ret void
+}
+
+define void @g() {
+; CHECK-LABEL: define void @g() local_unnamed_addr {
+; CHECK-NEXT:    tail call void @f()
+; CHECK-NEXT:    ret void
+;
+  call void @f()
+  ret void
+}
+
+define void @h() #0 {
+; CHECK-LABEL: define void @h(
+; CHECK-SAME: ) local_unnamed_addr #[[ATTR0]] {
+; CHECK-NEXT:    tail call void @d()
+; CHECK-NEXT:    tail call void @g()
+; CHECK-NEXT:    ret void
+;
+  call void @d()
+  call void @g()
+  ret void
+}
+
+attributes #0 = { "sign-return-address"="non-leaf" "sign-return-address-key"="a_key" }