[llvm] r327371 - bpf: Enhance debug information for peephole optimization passes

[Yonghong Song via llvm-commits]

Author: yhs
Date: Mon Mar 12 23:47:07 2018
New Revision: 327371

URL: http://llvm.org/viewvc/llvm-project?rev=327371&view=rev
Log:
bpf: Enhance debug information for peephole optimization passes

Add more debug information for peephole optimization passes.

These would only be enabled for debug version binary and could help
analyzing why some optimization opportunities were missed.

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=327371&r1=327370&r2=327371&view=diff
==============================================================================
--- llvm/trunk/lib/Target/BPF/BPFMIPeephole.cpp (original)
+++ llvm/trunk/lib/Target/BPF/BPFMIPeephole.cpp Mon Mar 12 23:47:07 2018
@@ -79,6 +79,9 @@ bool BPFMIPeephole::isMovFrom32Def(Machi
 {
   MachineInstr *DefInsn = MRI->getVRegDef(MovMI->getOperand(1).getReg());
 
+  DEBUG(dbgs() << "  Def of Mov Src:");
+  DEBUG(DefInsn->dump());
+
   if (!DefInsn)
     return false;
 
@@ -108,6 +111,8 @@ bool BPFMIPeephole::isMovFrom32Def(Machi
        return false;
   }
 
+  DEBUG(dbgs() << "  One ZExt elim sequence identified.\n");
+
   return true;
 }
 
@@ -134,21 +139,32 @@ bool BPFMIPeephole::eliminateZExtSeq(voi
         unsigned ShfReg = MI.getOperand(1).getReg();
         MachineInstr *SllMI = MRI->getVRegDef(ShfReg);
 
+        DEBUG(dbgs() << "Starting SRL found:");
+        DEBUG(MI.dump());
+
         if (!SllMI ||
             SllMI->isPHI() ||
             SllMI->getOpcode() != BPF::SLL_ri ||
             SllMI->getOperand(2).getImm() != 32)
           continue;
 
+        DEBUG(dbgs() << "  SLL found:");
+        DEBUG(SllMI->dump());
+
         MachineInstr *MovMI = MRI->getVRegDef(SllMI->getOperand(1).getReg());
         if (!MovMI ||
             MovMI->isPHI() ||
             MovMI->getOpcode() != BPF::MOV_32_64)
           continue;
 
+        DEBUG(dbgs() << "  Type cast Mov found:");
+        DEBUG(MovMI->dump());
+
         unsigned SubReg = MovMI->getOperand(1).getReg();
-        if (!isMovFrom32Def(MovMI))
+        if (!isMovFrom32Def(MovMI)) {
+          DEBUG(dbgs() << "  One ZExt elim sequence failed qualifying elim.\n");
           continue;
+        }
 
         BuildMI(MBB, MI, MI.getDebugLoc(), TII->get(BPF::SUBREG_TO_REG), DstReg)
           .addImm(0).addReg(SubReg).addImm(BPF::sub_32);
@@ -223,6 +239,8 @@ bool BPFMIPreEmitPeephole::eliminateRedu
     for (MachineInstr &MI : MBB) {
       // If the previous instruction was marked for elimination, remove it now.
       if (ToErase) {
+        DEBUG(dbgs() << "  Redundant Mov Eliminated:");
+        DEBUG(ToErase->dump());
         ToErase->eraseFromParent();
         ToErase = nullptr;
       }