[llvm] [BOLT] Enhance fixed indirect branch handling (PR #71324)

[Vladislav Khmelevsky via llvm-commits]

https://github.com/yota9 updated https://github.com/llvm/llvm-project/pull/71324

>From 548842085bf463106528d51f0f4012f8a0b65096 Mon Sep 17 00:00:00 2001
From: Vladislav Khmelevsky <och95 at yandex.ru>
Date: Sun, 5 Nov 2023 21:28:07 +0400
Subject: [PATCH] [BOLT] Enhance fixed indirect branch handling

Previously HasFixedIndirectBranch was set in BF to set isSimple to false
later because of unreachable bb ellimination pass which might remove the
BB with it's symbols accessed by other instructions than calls. It seems
to be that better solution would be to add extra entry point on target
offset instead of marking BF as non-simple.
---
 bolt/include/bolt/Core/BinaryFunction.h | 4 ----
 bolt/lib/Core/BinaryFunction.cpp        | 7 +------
 2 files changed, 1 insertion(+), 10 deletions(-)

diff --git a/bolt/include/bolt/Core/BinaryFunction.h b/bolt/include/bolt/Core/BinaryFunction.h
index c67ddccbf4892a7..c641bd6f3ce26b2 100644
--- a/bolt/include/bolt/Core/BinaryFunction.h
+++ b/bolt/include/bolt/Core/BinaryFunction.h
@@ -319,10 +319,6 @@ class BinaryFunction {
   /// Execution halts whenever this function is entered.
   bool TrapsOnEntry{false};
 
-  /// True if the function had an indirect branch with a fixed internal
-  /// destination.
-  bool HasFixedIndirectBranch{false};
-
   /// True if the function is a fragment of another function. This means that
   /// this function could only be entered via its parent or one of its sibling
   /// fragments. It could be entered at any basic block. It can also return
diff --git a/bolt/lib/Core/BinaryFunction.cpp b/bolt/lib/Core/BinaryFunction.cpp
index 2e1fa739e53f20b..89c05204da0b48c 100644
--- a/bolt/lib/Core/BinaryFunction.cpp
+++ b/bolt/lib/Core/BinaryFunction.cpp
@@ -430,8 +430,6 @@ void BinaryFunction::print(raw_ostream &OS, std::string Annotation) {
   OS << "\n  IsSplit     : " << isSplit();
   OS << "\n  BB Count    : " << size();
 
-  if (HasFixedIndirectBranch)
-    OS << "\n  HasFixedIndirectBranch : true";
   if (HasUnknownControlFlow)
     OS << "\n  Unknown CF  : true";
   if (getPersonalityFunction())
@@ -1116,7 +1114,7 @@ void BinaryFunction::handleIndirectBranch(MCInst &Instruction, uint64_t Size,
       Instruction.clear();
       MIB->createUncondBranch(Instruction, TargetSymbol, BC.Ctx.get());
       TakenBranches.emplace_back(Offset, IndirectTarget - getAddress());
-      HasFixedIndirectBranch = true;
+      addEntryPointAtOffset(IndirectTarget - getAddress());
     } else {
       MIB->convertJmpToTailCall(Instruction);
       BC.addInterproceduralReference(this, IndirectTarget);
@@ -1892,9 +1890,6 @@ bool BinaryFunction::postProcessIndirectBranches(
     LastIndirectJumpBB->updateJumpTableSuccessors();
   }
 
-  if (HasFixedIndirectBranch)
-    return false;
-
   // Validate that all data references to function offsets are claimed by
   // recognized jump tables. Register externally referenced blocks as entry
   // points.