1 files changed, 21 insertions, 1 deletions
diff --git a/llvm/lib/CodeGen/PeepholeOptimizer.cpp b/llvm/lib/CodeGen/PeepholeOptimizer.cpp
index 729a57e..e1d39d6 100644
--- a/llvm/lib/CodeGen/PeepholeOptimizer.cpp
+++ b/llvm/lib/CodeGen/PeepholeOptimizer.cpp
@@ -1929,7 +1929,27 @@ ValueTrackerResult ValueTracker::getNextSourceFromCopy() {
   const MachineOperand &Src = Def->getOperand(1);
   if (Src.isUndef())
     return ValueTrackerResult();
-  return ValueTrackerResult(Src.getReg(), Src.getSubReg());
+
+  Register SrcReg = Src.getReg();
+  unsigned SubReg = Src.getSubReg();
+  if (DefSubReg) {
+    const TargetRegisterInfo *TRI = MRI.getTargetRegisterInfo();
+    SubReg = TRI->composeSubRegIndices(SubReg, DefSubReg);
+
+    if (SrcReg.isVirtual()) {
+      // TODO: Try constraining on rewrite if we can
+      const TargetRegisterClass *RegRC = MRI.getRegClass(SrcReg);
+      const TargetRegisterClass *SrcWithSubRC =
+          TRI->getSubClassWithSubReg(RegRC, SubReg);
+      if (RegRC != SrcWithSubRC)
+        return ValueTrackerResult();
+    } else {
+      if (!TRI->getSubReg(SrcReg, SubReg))
+        return ValueTrackerResult();
+    }
+  }
+
+  return ValueTrackerResult(SrcReg, SubReg);
 }
 
 ValueTrackerResult ValueTracker::getNextSourceFromBitcast() {