[mips][microMIPS] This patch implements functionality in MIPS delay slot

filler such as if delay slot filler have to put NOP instruction into the
delay slot of microMIPS BEQ or BNE instruction which uses the register $0,
then instead of emitting NOP this instruction is replaced by the corresponding
microMIPS compact branch instruction, i.e. BEQZC or BNEZC.

Differential Revision: http://reviews.llvm.org/D3566

llvm-svn: 222580

llvm/lib/Target/Mips/MipsDelaySlotFiller.cpp

@@ -196,6 +196,9 @@ namespace {
   private:
     bool runOnMachineBasicBlock(MachineBasicBlock &MBB);
 
+    Iter replaceWithCompactBranch(MachineBasicBlock &MBB,
+                                  Iter Branch, DebugLoc DL);
+
     /// This function checks if it is valid to move Candidate to the delay slot
     /// and returns true if it isn't. It also updates memory and register
     /// dependence information.
@@ -494,6 +497,29 @@ getUnderlyingObjects(const MachineInstr &MI,
   return true;
 }
 
+// Replace Branch with the compact branch instruction.
+Iter Filler::replaceWithCompactBranch(MachineBasicBlock &MBB,
+                                      Iter Branch, DebugLoc DL) {
+  const MipsInstrInfo *TII= static_cast<const MipsInstrInfo *>(
+    TM.getSubtargetImpl()->getInstrInfo());
+
+  unsigned NewOpcode =
+    (((unsigned) Branch->getOpcode()) == Mips::BEQ) ? Mips::BEQZC_MM
+                                                    : Mips::BNEZC_MM;
+
+  const MCInstrDesc &NewDesc = TII->get(NewOpcode);
+  MachineInstrBuilder MIB = BuildMI(MBB, Branch, DL, NewDesc);
+
+  MIB.addReg(Branch->getOperand(0).getReg());
+  MIB.addMBB(Branch->getOperand(2).getMBB());
+
+  Iter tmpIter = Branch;
+  Branch = std::prev(Branch);
+  MBB.erase(tmpIter);
+
+  return Branch;
+}
+
 /// runOnMachineBasicBlock - Fill in delay slots for the given basic block.
 /// We assume there is only one delay slot per delayed instruction.
 bool Filler::runOnMachineBasicBlock(MachineBasicBlock &MBB) {
@@ -527,11 +553,23 @@ bool Filler::runOnMachineBasicBlock(MachineBasicBlock &MBB) {
       }
     }
 
-    // Bundle the NOP to the instruction with the delay slot.
-    const MipsInstrInfo *TII = static_cast<const MipsInstrInfo *>(
-        TM.getSubtargetImpl()->getInstrInfo());
-    BuildMI(MBB, std::next(I), I->getDebugLoc(), TII->get(Mips::NOP));
-    MIBundleBuilder(MBB, I, std::next(I, 2));
+    // If instruction is BEQ or BNE with one ZERO register, then instead of
+    // adding NOP replace this instruction with the corresponding compact
+    // branch instruction, i.e. BEQZC or BNEZC.
+    unsigned Opcode = I->getOpcode();
+    if (InMicroMipsMode &&
+        (Opcode == Mips::BEQ || Opcode == Mips::BNE) &&
+        ((unsigned) I->getOperand(1).getReg()) == Mips::ZERO) {
+
+      I = replaceWithCompactBranch(MBB, I, I->getDebugLoc());
+
+    } else {
+      // Bundle the NOP to the instruction with the delay slot.
+      const MipsInstrInfo *TII = static_cast<const MipsInstrInfo *>(
+          TM.getSubtargetImpl()->getInstrInfo());
+      BuildMI(MBB, std::next(I), I->getDebugLoc(), TII->get(Mips::NOP));
+      MIBundleBuilder(MBB, I, std::next(I, 2));
+    }
   }
 
   return Changed;

llvm/lib/Target/Mips/MipsLongBranch.cpp

@@ -237,11 +237,13 @@ void MipsLongBranch::replaceBranch(MachineBasicBlock &MBB, Iter Br,
 
   MIB.addMBB(MBBOpnd);
 
-  // Bundle the instruction in the delay slot to the newly created branch
-  // and erase the original branch.
-  assert(Br->isBundledWithSucc());
-  MachineBasicBlock::instr_iterator II(Br);
-  MIBundleBuilder(&*MIB).append((++II)->removeFromBundle());
+  if (Br->hasDelaySlot()) {
+    // Bundle the instruction in the delay slot to the newly created branch
+    // and erase the original branch.
+    assert(Br->isBundledWithSucc());
+    MachineBasicBlock::instr_iterator II(Br);
+    MIBundleBuilder(&*MIB).append((++II)->removeFromBundle());
+  }
   Br->eraseFromParent();
 }
 

llvm/lib/Target/Mips/MipsSEInstrInfo.cpp

@@ -352,6 +352,8 @@ unsigned MipsSEInstrInfo::getOppositeBranchOpc(unsigned Opc) const {
   case Mips::BLEZ64: return Mips::BGTZ64;
   case Mips::BC1T:   return Mips::BC1F;
   case Mips::BC1F:   return Mips::BC1T;
+  case Mips::BEQZC_MM: return Mips::BNEZC_MM;
+  case Mips::BNEZC_MM: return Mips::BEQZC_MM;
   }
 }
 
@@ -422,7 +424,7 @@ unsigned MipsSEInstrInfo::getAnalyzableBrOpc(unsigned Opc) const {
           Opc == Mips::BEQ64  || Opc == Mips::BNE64  || Opc == Mips::BGTZ64 ||
           Opc == Mips::BGEZ64 || Opc == Mips::BLTZ64 || Opc == Mips::BLEZ64 ||
           Opc == Mips::BC1T   || Opc == Mips::BC1F   || Opc == Mips::B      ||
-          Opc == Mips::J) ?
+          Opc == Mips::J || Opc == Mips::BEQZC_MM || Opc == Mips::BNEZC_MM) ?
          Opc : 0;
 }
 

llvm/test/CodeGen/Mips/micromips-atomic.ll

@@ -14,5 +14,5 @@ entry:
 ; CHECK:   ll      $[[R1:[0-9]+]], 0($[[R0]])
 ; CHECK:   addu    $[[R2:[0-9]+]], $[[R1]], $4
 ; CHECK:   sc      $[[R2]], 0($[[R0]])
-; CHECK:   beqz    $[[R2]], $[[BB0]]
+; CHECK:   beqzc   $[[R2]], $[[BB0]]
 }

llvm/test/CodeGen/Mips/micromips-compact-branches.ll

@@ -0,0 +1,19 @@
+; RUN: llc %s -march=mipsel -mattr=micromips -filetype=asm -O3 \
+; RUN: -disable-mips-delay-filler -relocation-model=pic -o - | FileCheck %s
+
+define void @main() nounwind uwtable {
+entry:
+  %x = alloca i32, align 4
+  %0 = load i32* %x, align 4
+  %cmp = icmp eq i32 %0, 0
+  br i1 %cmp, label %if.then, label %if.end
+
+if.then:
+  store i32 10, i32* %x, align 4
+  br label %if.end
+
+if.end:
+  ret void
+}
+
+; CHECK: bnezc