[llvm] [AMDGPU][MachineRegisterInfo] Extend the MRI live-ins check to account for Subreg (PR #126926)

[Vikash Gupta via llvm-commits]

https://github.com/vg0204 updated https://github.com/llvm/llvm-project/pull/126926

>From 1b35f74721e3331f58409c941c1472c1e40cbe21 Mon Sep 17 00:00:00 2001
From: vikashgu <Vikash.Gupta at amd.com>
Date: Wed, 12 Feb 2025 15:23:23 +0000
Subject: [PATCH 1/2] [AMDGPU][MachineRegisterInfo] Extend the MRI live-ins
 check by including the check against the subregs for live-ins.

---
 llvm/include/llvm/CodeGen/MachineRegisterInfo.h |  2 +-
 llvm/lib/CodeGen/MachineRegisterInfo.cpp        | 16 ++++++++++++++--
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/llvm/include/llvm/CodeGen/MachineRegisterInfo.h b/llvm/include/llvm/CodeGen/MachineRegisterInfo.h
index 1c465741cb462..f182b42d2a24a 100644
--- a/llvm/include/llvm/CodeGen/MachineRegisterInfo.h
+++ b/llvm/include/llvm/CodeGen/MachineRegisterInfo.h
@@ -1020,7 +1020,7 @@ class MachineRegisterInfo {
     return LiveIns;
   }
 
-  bool isLiveIn(Register Reg) const;
+  bool isLiveIn(Register Reg, bool CheckForSubreg = false) const;
 
   /// getLiveInPhysReg - If VReg is a live-in virtual register, return the
   /// corresponding live-in physical register.
diff --git a/llvm/lib/CodeGen/MachineRegisterInfo.cpp b/llvm/lib/CodeGen/MachineRegisterInfo.cpp
index 937f63f6c5e00..341b0c7207092 100644
--- a/llvm/lib/CodeGen/MachineRegisterInfo.cpp
+++ b/llvm/lib/CodeGen/MachineRegisterInfo.cpp
@@ -447,10 +447,22 @@ void MachineRegisterInfo::clearKillFlags(Register Reg) const {
     MO.setIsKill(false);
 }
 
-bool MachineRegisterInfo::isLiveIn(Register Reg) const {
-  for (const std::pair<MCRegister, Register> &LI : liveins())
+bool MachineRegisterInfo::isLiveIn(Register Reg, bool CheckForSubreg) const {
+  for (const std::pair<MCRegister, Register> &LI : liveins()) {
     if ((Register)LI.first == Reg || LI.second == Reg)
       return true;
+
+    // Check if Reg is a subreg of live-in register
+    if (CheckForSubreg) {
+      MCRegister PhysReg = LI.first;
+      if (!PhysReg.isValid())
+        continue;
+
+      for (MCPhysReg SubReg : getTargetRegisterInfo()->subregs(PhysReg))
+        if (SubReg == Reg)
+          return true;
+    }
+  }
   return false;
 }
 

>From efc25870025d5d45976abde8d3cff2fddfe14178 Mon Sep 17 00:00:00 2001
From: vikashgu <Vikash.Gupta at amd.com>
Date: Thu, 13 Feb 2025 07:17:45 +0000
Subject: [PATCH 2/2] Modified MRI liviIn check to have unconditional subreg
 check

---
 llvm/include/llvm/CodeGen/MachineRegisterInfo.h |  2 +-
 llvm/lib/CodeGen/MachineRegisterInfo.cpp        | 16 +++++++---------
 2 files changed, 8 insertions(+), 10 deletions(-)

diff --git a/llvm/include/llvm/CodeGen/MachineRegisterInfo.h b/llvm/include/llvm/CodeGen/MachineRegisterInfo.h
index f182b42d2a24a..1c465741cb462 100644
--- a/llvm/include/llvm/CodeGen/MachineRegisterInfo.h
+++ b/llvm/include/llvm/CodeGen/MachineRegisterInfo.h
@@ -1020,7 +1020,7 @@ class MachineRegisterInfo {
     return LiveIns;
   }
 
-  bool isLiveIn(Register Reg, bool CheckForSubreg = false) const;
+  bool isLiveIn(Register Reg) const;
 
   /// getLiveInPhysReg - If VReg is a live-in virtual register, return the
   /// corresponding live-in physical register.
diff --git a/llvm/lib/CodeGen/MachineRegisterInfo.cpp b/llvm/lib/CodeGen/MachineRegisterInfo.cpp
index 341b0c7207092..edac380dcf363 100644
--- a/llvm/lib/CodeGen/MachineRegisterInfo.cpp
+++ b/llvm/lib/CodeGen/MachineRegisterInfo.cpp
@@ -447,21 +447,19 @@ void MachineRegisterInfo::clearKillFlags(Register Reg) const {
     MO.setIsKill(false);
 }
 
-bool MachineRegisterInfo::isLiveIn(Register Reg, bool CheckForSubreg) const {
+bool MachineRegisterInfo::isLiveIn(Register Reg) const {
   for (const std::pair<MCRegister, Register> &LI : liveins()) {
     if ((Register)LI.first == Reg || LI.second == Reg)
       return true;
 
     // Check if Reg is a subreg of live-in register
-    if (CheckForSubreg) {
-      MCRegister PhysReg = LI.first;
-      if (!PhysReg.isValid())
-        continue;
+    MCRegister PhysReg = LI.first;
+    if (!PhysReg.isValid())
+      continue;
 
-      for (MCPhysReg SubReg : getTargetRegisterInfo()->subregs(PhysReg))
-        if (SubReg == Reg)
-          return true;
-    }
+    for (MCPhysReg SubReg : getTargetRegisterInfo()->subregs(PhysReg))
+      if (SubReg == Reg)
+        return true;
   }
   return false;
 }