Add a trivial but handy function to efficiently return the machine

instruction that defines the specified vreg.  Crazy.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45480 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/MachineRegisterInfo.h

@@ -120,6 +120,12 @@ public:
     return VRegInfo.size()+MRegisterInfo::FirstVirtualRegister-1;
   }
   
+  /// getVRegDef - Return the machine instr that defines the specified virtual
+  /// register or null if none is found.  This assumes that the code is in SSA
+  /// form, so there should only be one definition.
+  MachineInstr *getVRegDef(unsigned Reg) const;
+  
+  
   //===--------------------------------------------------------------------===//
   // Physical Register Use Info
   //===--------------------------------------------------------------------===//

lib/CodeGen/MachineRegisterInfo.cpp

@@ -44,3 +44,18 @@ void MachineRegisterInfo::HandleVRegListReallocation() {
     List->Contents.Reg.Prev = &VRegInfo[i].second;
   }
 }
+
+
+/// getVRegDef - Return the machine instr that defines the specified virtual
+/// register or null if none is found.  This assumes that the code is in SSA
+/// form, so there should only be one definition.
+MachineInstr *MachineRegisterInfo::getVRegDef(unsigned Reg) const {
+  assert(Reg-MRegisterInfo::FirstVirtualRegister < VRegInfo.size() &&
+         "Invalid vreg!");
+  for (reg_iterator I = reg_begin(Reg), E = reg_end(); I != E; ++I) {
+    // Since we are in SSA form, we can stop at the first definition.
+    if (I->isDef())
+      return I->getParent();
+  }
+  return 0;
+}