[llvm] r327368 - bpf: Support subregister definition check on PHI node

[Yonghong Song via llvm-commits]

Author: yhs
Date: Mon Mar 12 23:47:04 2018
New Revision: 327368

URL: http://llvm.org/viewvc/llvm-project?rev=327368&view=rev
Log:
bpf: Support subregister definition check on PHI node

This patch relax the subregister definition check on Phi node.
Previously, we just cancel the optimizatoin when the definition is Phi
node while actually we could further check the definitions of incoming
parameters of PHI node.

This helps catch more elimination opportunities.

Signed-off-by: Jiong Wang <jiong.wang at netronome.com>
Signed-off-by: Yonghong Song <yhs at fb.com>

Modified:
    llvm/trunk/lib/Target/BPF/BPFMIPeephole.cpp

Modified: llvm/trunk/lib/Target/BPF/BPFMIPeephole.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/BPF/BPFMIPeephole.cpp?rev=327368&r1=327367&r2=327368&view=diff
==============================================================================
--- llvm/trunk/lib/Target/BPF/BPFMIPeephole.cpp (original)
+++ llvm/trunk/lib/Target/BPF/BPFMIPeephole.cpp Mon Mar 12 23:47:04 2018
@@ -76,9 +76,23 @@ bool BPFMIPeephole::isMovFrom32Def(Machi
 {
   MachineInstr *DefInsn = MRI->getVRegDef(MovMI->getOperand(1).getReg());
 
-  if (!DefInsn || DefInsn->isPHI())
+  if (!DefInsn)
     return false;
 
+  if (DefInsn->isPHI()) {
+    for (unsigned i = 1, e = DefInsn->getNumOperands(); i < e; i += 2) {
+      MachineOperand &opnd = DefInsn->getOperand(i);
+
+      if (!opnd.isReg())
+        return false;
+
+      MachineInstr *PhiDef = MRI->getVRegDef(opnd.getReg());
+      // quick check on PHI incoming definitions.
+      if (!PhiDef || PhiDef->isPHI() || PhiDef->getOpcode() == BPF::COPY)
+        return false;
+    }
+  }
+
   if (DefInsn->getOpcode() == BPF::COPY) {
     MachineOperand &opnd = DefInsn->getOperand(1);
 
@@ -129,10 +143,10 @@ bool BPFMIPeephole::eliminateZExtSeq(voi
             MovMI->getOpcode() != BPF::MOV_32_64)
           continue;
 
+        unsigned SubReg = MovMI->getOperand(1).getReg();
         if (!isMovFrom32Def(MovMI))
           continue;
 
-        unsigned SubReg = MovMI->getOperand(1).getReg();
         BuildMI(MBB, MI, MI.getDebugLoc(), TII->get(BPF::SUBREG_TO_REG), DstReg)
           .addImm(0).addReg(SubReg).addImm(BPF::sub_32);