From 18842783cc0d442d292ae4fd40c8c04c4e8702c4 Mon Sep 17 00:00:00 2001
From: Jakob Stoklund Olesen <stoklund@2pi.dk>
Date: Wed, 6 Oct 2010 23:54:39 +0000
Subject: [PATCH] Add MachineRegisterInfo::constrainRegClass and use it in
 MachineCSE.

This function is intended to be used when inserting a machine instruction that
trivially restricts the legal registers, like LEA requiring a GR32_NOSP
argument.

llvm-svn: 115875
---
 llvm/include/llvm/CodeGen/MachineRegisterInfo.h |  8 ++++++++
 llvm/lib/CodeGen/MachineCSE.cpp                 |  9 ++-------
 llvm/lib/CodeGen/MachineRegisterInfo.cpp        | 14 ++++++++++++++
 3 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/llvm/include/llvm/CodeGen/MachineRegisterInfo.h b/llvm/include/llvm/CodeGen/MachineRegisterInfo.h
index 066c91b36cf5..ddba61bf189a 100644
--- a/llvm/include/llvm/CodeGen/MachineRegisterInfo.h
+++ b/llvm/include/llvm/CodeGen/MachineRegisterInfo.h
@@ -203,6 +203,14 @@ public:
   ///
   void setRegClass(unsigned Reg, const TargetRegisterClass *RC);
 
+  /// constrainRegClass - Constrain the register class of the specified virtual
+  /// register to be a common subclass of RC and the current register class.
+  /// Return the new register class, or NULL if no such class exists.
+  /// This should only be used when the constraint is known to be trivial, like
+  /// GR32 -> GR32_NOSP. Beware of increasing register pressure.
+  const TargetRegisterClass *constrainRegClass(unsigned Reg,
+                                               const TargetRegisterClass *RC);
+
   /// createVirtualRegister - Create and return a new virtual register in the
   /// function with the specified register class.
   ///
diff --git a/llvm/lib/CodeGen/MachineCSE.cpp b/llvm/lib/CodeGen/MachineCSE.cpp
index 272b54dea1fa..9d09f608ee91 100644
--- a/llvm/lib/CodeGen/MachineCSE.cpp
+++ b/llvm/lib/CodeGen/MachineCSE.cpp
@@ -120,17 +120,12 @@ bool MachineCSE::PerformTrivialCoalescing(MachineInstr *MI,
       continue;
     if (DefMI->getOperand(0).getSubReg() || DefMI->getOperand(1).getSubReg())
       continue;
-    const TargetRegisterClass *SRC   = MRI->getRegClass(SrcReg);
-    const TargetRegisterClass *RC    = MRI->getRegClass(Reg);
-    const TargetRegisterClass *NewRC = getCommonSubClass(RC, SRC);
-    if (!NewRC)
+    if (!MRI->constrainRegClass(SrcReg, MRI->getRegClass(Reg)))
       continue;
     DEBUG(dbgs() << "Coalescing: " << *DefMI);
-    DEBUG(dbgs() << "*** to: " << *MI);
+    DEBUG(dbgs() << "***     to: " << *MI);
     MO.setReg(SrcReg);
     MRI->clearKillFlags(SrcReg);
-    if (NewRC != SRC)
-      MRI->setRegClass(SrcReg, NewRC);
     DefMI->eraseFromParent();
     ++NumCoalesces;
     Changed = true;
diff --git a/llvm/lib/CodeGen/MachineRegisterInfo.cpp b/llvm/lib/CodeGen/MachineRegisterInfo.cpp
index 5d852f26beda..7b839f07e73c 100644
--- a/llvm/lib/CodeGen/MachineRegisterInfo.cpp
+++ b/llvm/lib/CodeGen/MachineRegisterInfo.cpp
@@ -60,6 +60,20 @@ MachineRegisterInfo::setRegClass(unsigned Reg, const TargetRegisterClass *RC) {
   RegClass2VRegMap[RC->getID()].push_back(VR);
 }
 
+const TargetRegisterClass *
+MachineRegisterInfo::constrainRegClass(unsigned Reg,
+                                       const TargetRegisterClass *RC) {
+  const TargetRegisterClass *OldRC = getRegClass(Reg);
+  if (OldRC == RC)
+    return RC;
+  const TargetRegisterClass *NewRC = getCommonSubClass(OldRC, RC);
+  if (!NewRC)
+    return 0;
+  if (NewRC != OldRC)
+    setRegClass(Reg, NewRC);
+  return NewRC;
+}
+
 /// createVirtualRegister - Create and return a new virtual register in the
 /// function with the specified register class.
 ///