Fix some issues with rematerialization in RegisterCoalescer when the destination

of the copy is a subregister def. The current code assumes that it can do a full
def of the destination register, but it is not checking that the def operand is
read-undef. It also doesn't clear the subregister index of the destination in
the new instruction to reflect the full subregister def.

These issues were found running 'make check' with my next commit that enables
rematerialization in more cases.

llvm-svn: 175122

diff --git a/llvm/lib/CodeGen/RegisterCoalescer.cpp b/llvm/lib/CodeGen/RegisterCoalescer.cpp
index e682d63c8fe1c495512582e4eca0ebd4c8d1f297..dfd9b8609f943fa72c4be4afaf28fa1308c810bb 100644 (file)
--- a/llvm/lib/CodeGen/RegisterCoalescer.cpp
+++ b/llvm/lib/CodeGen/RegisterCoalescer.cpp
@@ -755,6 +755,10 @@ bool RegisterCoalescer::reMaterializeTrivialDef(LiveInterval &SrcInt,
   const MCInstrDesc &MCID = DefMI->getDesc();
   if (MCID.getNumDefs() != 1)
     return false;
+  // Only support subregister destinations when the def is read-undef.
+  MachineOperand &DstOperand = CopyMI->getOperand(0);
+  if (DstOperand.getSubReg() && !DstOperand.isUndef())
+    return false;
   if (!DefMI->isImplicitDef()) {
     // Make sure the copy destination register class fits the instruction
     // definition register class. The mismatch can happen as a result of earlier
@@ -773,6 +777,12 @@ bool RegisterCoalescer::reMaterializeTrivialDef(LiveInterval &SrcInt,
   TII->reMaterialize(*MBB, MII, DstReg, 0, DefMI, *TRI);
   MachineInstr *NewMI = prior(MII);
 
+  // The original DefMI may have been a subregister def, but the full register
+  // class of its destination matches the destination of CopyMI, and CopyMI is
+  // either a full register def or is read-undef. Therefore we can clear the
+  // subregister index on the rematerialized instruction.
+  NewMI->getOperand(0).setSubReg(0);
+
   // NewMI may have dead implicit defs (E.g. EFLAGS for MOV<bits>r0 on X86).
   // We need to remember these so we can add intervals once we insert
   // NewMI into SlotIndexes.