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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@115875 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 16 insertions, 7 deletions

diff --git a/lib/CodeGen/MachineCSE.cpp b/lib/CodeGen/MachineCSE.cpp
index 272b54dea1..9d09f608ee 100644
--- a/lib/CodeGen/MachineCSE.cpp
+++ b/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/lib/CodeGen/MachineRegisterInfo.cpp b/lib/CodeGen/MachineRegisterInfo.cpp
index 5d852f26be..7b839f07e7 100644
--- a/lib/CodeGen/MachineRegisterInfo.cpp
+++ b/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.
 ///