Add a MinNumRegs argument to MRI::constrainRegClass().

The function will refuse to use a register class with fewer registers
than MinNumRegs.  This can be used by clients to avoid accidentally
increase register pressure too much.

The default value of MinNumRegs=0 doesn't affect how constrainRegClass()
works.

llvm-svn: 140339

1 files changed, 6 insertions, 4 deletions

diff --git a/llvm/lib/CodeGen/MachineRegisterInfo.cpp b/llvm/lib/CodeGen/MachineRegisterInfo.cpp
index d7953896be1..d513f29e7c1 100644
--- a/llvm/lib/CodeGen/MachineRegisterInfo.cpp
+++ b/llvm/lib/CodeGen/MachineRegisterInfo.cpp
@@ -49,15 +49,17 @@ MachineRegisterInfo::setRegClass(unsigned Reg, const TargetRegisterClass *RC) {
 
 const TargetRegisterClass *
 MachineRegisterInfo::constrainRegClass(unsigned Reg,
-                                       const TargetRegisterClass *RC) {
+                                       const TargetRegisterClass *RC,
+                                       unsigned MinNumRegs) {
   const TargetRegisterClass *OldRC = getRegClass(Reg);
   if (OldRC == RC)
     return RC;
   const TargetRegisterClass *NewRC = getCommonSubClass(OldRC, RC);
-  if (!NewRC)
+  if (!NewRC || NewRC == OldRC)
+    return NewRC;
+  if (NewRC->getNumRegs() < MinNumRegs)
     return 0;
-  if (NewRC != OldRC)
-    setRegClass(Reg, NewRC);
+  setRegClass(Reg, NewRC);
   return NewRC;
 }