[llvm] [PostRASink] Add target hook shouldPostRASink (PR #167182)

[Junjie Gu via llvm-commits]

https://github.com/jgu222 updated https://github.com/llvm/llvm-project/pull/167182

>From 3813766bcca30034a1824e3d6ffa2612dc38632e Mon Sep 17 00:00:00 2001
From: "Gu, Junjie" <junjie.gu at intel.com>
Date: Sat, 8 Nov 2025 12:10:14 -0800
Subject: [PATCH] [PostRASink] Add target hook shouldPostRASink

Some target may choose not to sink some instructions. This hook
allows targets to control it.
---
 llvm/include/llvm/CodeGen/TargetInstrInfo.h | 3 +++
 llvm/lib/CodeGen/MachineSink.cpp            | 4 ++++
 2 files changed, 7 insertions(+)

diff --git a/llvm/include/llvm/CodeGen/TargetInstrInfo.h b/llvm/include/llvm/CodeGen/TargetInstrInfo.h
index 2dcedfb40f3e6..7010cffe23a11 100644
--- a/llvm/include/llvm/CodeGen/TargetInstrInfo.h
+++ b/llvm/include/llvm/CodeGen/TargetInstrInfo.h
@@ -436,7 +436,10 @@ class LLVM_ABI TargetInstrInfo : public MCInstrInfo {
   /// MachineSink determines on its own whether the instruction is safe to sink;
   /// this gives the target a hook to override the default behavior with regards
   /// to which instructions should be sunk.
+  ///
+  /// shouldPostRASink() is used by PostRAMachineSink.
   virtual bool shouldSink(const MachineInstr &MI) const { return true; }
+  virtual bool shouldPostRASink(const MachineInstr &MI) const { return true; }
 
   /// Return false if the instruction should not be hoisted by MachineLICM.
   ///
diff --git a/llvm/lib/CodeGen/MachineSink.cpp b/llvm/lib/CodeGen/MachineSink.cpp
index cdcb29d92bfe6..94ed82eee9b8f 100644
--- a/llvm/lib/CodeGen/MachineSink.cpp
+++ b/llvm/lib/CodeGen/MachineSink.cpp
@@ -2287,6 +2287,10 @@ bool PostRAMachineSinkingImpl::tryToSinkCopy(MachineBasicBlock &CurBB,
       continue;
     }
 
+    // Don't postRASink instructions that the target prefers not to sink.
+    if (!TII->shouldPostRASink(MI))
+      continue;
+
     if (MI.isDebugOrPseudoInstr())
       continue;