[CodeGen] Enhance createFrom for sub-reg aware cloningusers/cdevadas/enhance-createFrom-function

Instead of just cloning the virtual register, this
function now creates a new virtual register derived
from a subregister class of the original value.

1 files changed, 9 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/LiveRangeEdit.cpp b/llvm/lib/CodeGen/LiveRangeEdit.cpp
index 6fe1170..d8a2ad4 100644
--- a/llvm/lib/CodeGen/LiveRangeEdit.cpp
+++ b/llvm/lib/CodeGen/LiveRangeEdit.cpp
@@ -52,8 +52,16 @@ LiveInterval &LiveRangeEdit::createEmptyIntervalFrom(Register OldReg,
   return LI;
 }
 
-Register LiveRangeEdit::createFrom(Register OldReg) {
+Register LiveRangeEdit::createFrom(Register OldReg,
+                                   const TargetRegisterClass *RC) {
   Register VReg = MRI.cloneVirtualRegister(OldReg);
+
+  // If RC is given, set it now. This is needed for cloning a new VReg with a
+  // smaller RC from its original virtual register, mainly used for subreg
+  // reload. The cloning is done first to ensure the vreg flags are preserved.
+  if (RC)
+    MRI.setRegClass(VReg, RC);
+
   if (VRM) {
     VRM->setIsSplitFromReg(VReg, VRM->getOriginal(OldReg));
   }