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@netronome.com>
Signed-off-by: Yonghong Song <yhs@fb.com>
llvm-svn: 327368

1 files changed, 16 insertions, 2 deletions

diff --git a/llvm/lib/Target/BPF/BPFMIPeephole.cpp b/llvm/lib/Target/BPF/BPFMIPeephole.cpp
index b15a7e6663e..cf26f2436fa 100644
--- a/llvm/lib/Target/BPF/BPFMIPeephole.cpp
+++ b/llvm/lib/Target/BPF/BPFMIPeephole.cpp
@@ -76,9 +76,23 @@ bool BPFMIPeephole::isMovFrom32Def(MachineInstr *MovMI)
 {
   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(void) {
             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);