It's not safe to remove SUBREG_TO_REG that looks like identity copies, e.g. movl %eax, %eax on x86-64 actually does a zero-extend.

llvm-svn: 52421

1 files changed, 6 insertions, 11 deletions

diff --git a/llvm/lib/CodeGen/LowerSubregs.cpp b/llvm/lib/CodeGen/LowerSubregs.cpp
index 296e6d45c34..e2e68d86713 100644
--- a/llvm/lib/CodeGen/LowerSubregs.cpp
+++ b/llvm/lib/CodeGen/LowerSubregs.cpp
@@ -108,20 +108,15 @@ bool LowerSubregsInstructionPass::LowerSubregToReg(MachineInstr *MI) {
 
   DOUT << "subreg: CONVERTING: " << *MI;
 
-  if (DstSubReg == InsReg) {
-    // No need to insert an identify copy instruction.
-    DOUT << "subreg: eliminated!";
-  } else {
-    // Insert sub-register copy
-    const TargetRegisterClass *TRC0= TRI.getPhysicalRegisterRegClass(DstSubReg);
-    const TargetRegisterClass *TRC1= TRI.getPhysicalRegisterRegClass(InsReg);
-    TII.copyRegToReg(*MBB, MI, DstSubReg, InsReg, TRC0, TRC1);
+  // Insert sub-register copy
+  const TargetRegisterClass *TRC0= TRI.getPhysicalRegisterRegClass(DstSubReg);
+  const TargetRegisterClass *TRC1= TRI.getPhysicalRegisterRegClass(InsReg);
+  TII.copyRegToReg(*MBB, MI, DstSubReg, InsReg, TRC0, TRC1);
 
 #ifndef NDEBUG
-    MachineBasicBlock::iterator dMI = MI;
-    DOUT << "subreg: " << *(--dMI);
+  MachineBasicBlock::iterator dMI = MI;
+  DOUT << "subreg: " << *(--dMI);
 #endif
-  }
 
   DOUT << "\n";
   MBB->remove(MI);