[RISCV] Add short forward branch support for min, max, maxu and minu

llvm/lib/Target/RISCV/RISCVExpandPseudoInsts.cpp

@@ -221,6 +221,7 @@ bool RISCVExpandPseudo::expandCCOp(MachineBasicBlock &MBB,
         .addImm(0);
   } else {
     unsigned NewOpc;
+    // clang-format off
     switch (MI.getOpcode()) {
     default:
       llvm_unreachable("Unexpected opcode!");
@@ -232,18 +233,10 @@ bool RISCVExpandPseudo::expandCCOp(MachineBasicBlock &MBB,
     case RISCV::PseudoCCAND:   NewOpc = RISCV::AND;   break;
     case RISCV::PseudoCCOR:    NewOpc = RISCV::OR;    break;
     case RISCV::PseudoCCXOR:   NewOpc = RISCV::XOR;   break;
-    case RISCV::PseudoCCMAX:
-      NewOpc = RISCV::MAX;
-      break;
-    case RISCV::PseudoCCMIN:
-      NewOpc = RISCV::MIN;
-      break;
-    case RISCV::PseudoCCMAXU:
-      NewOpc = RISCV::MAXU;
-      break;
-    case RISCV::PseudoCCMINU:
-      NewOpc = RISCV::MINU;
-      break;
+    case RISCV::PseudoCCMAX:   NewOpc = RISCV::MAX;   break;
+    case RISCV::PseudoCCMIN:   NewOpc = RISCV::MIN;   break;
+    case RISCV::PseudoCCMAXU:  NewOpc = RISCV::MAXU;  break;
+    case RISCV::PseudoCCMINU:  NewOpc = RISCV::MINU;  break;
     case RISCV::PseudoCCADDI:  NewOpc = RISCV::ADDI;  break;
     case RISCV::PseudoCCSLLI:  NewOpc = RISCV::SLLI;  break;
     case RISCV::PseudoCCSRLI:  NewOpc = RISCV::SRLI;  break;
@@ -266,6 +259,7 @@ bool RISCVExpandPseudo::expandCCOp(MachineBasicBlock &MBB,
     case RISCV::PseudoCCNDS_BFOS: NewOpc = RISCV::NDS_BFOS; break;
     case RISCV::PseudoCCNDS_BFOZ: NewOpc = RISCV::NDS_BFOZ; break;
     }
+    // clang-format on
 
     if (NewOpc == RISCV::NDS_BFOZ || NewOpc == RISCV::NDS_BFOS) {
       BuildMI(TrueBB, DL, TII->get(NewOpc), DestReg)

llvm/lib/Target/RISCV/RISCVFeatures.td

@@ -1850,6 +1850,10 @@ def TuneShortForwardBranchOpt
 def HasShortForwardBranchOpt : Predicate<"Subtarget->hasShortForwardBranchOpt()">;
 def NoShortForwardBranchOpt : Predicate<"!Subtarget->hasShortForwardBranchOpt()">;
 
+def TuneShortForwardBranchIMinMax
+    : SubtargetFeature<"short-forward-branch-i-minmax", "HasShortForwardBranchIMinMax",
+                       "true", "Enable short forward branch optimization for min,max instructions in Zbb", [TuneShortForwardBranchOpt]>;
+
 // Some subtargets require a S2V transfer buffer to move scalars into vectors.
 // FIXME: Forming .vx/.vf/.wx/.wf can reduce register pressure.
 def TuneNoSinkSplatOperands

llvm/lib/Target/RISCV/RISCVInstrInfo.cpp

@@ -1739,14 +1739,21 @@ unsigned getPredicatedOpcode(unsigned Opcode) {
 /// return the defining instruction.
 static MachineInstr *canFoldAsPredicatedOp(Register Reg,
                                            const MachineRegisterInfo &MRI,
-                                           const TargetInstrInfo *TII) {
+                                           const TargetInstrInfo *TII,
+                                           bool minmax) {
   if (!Reg.isVirtual())
     return nullptr;
   if (!MRI.hasOneNonDBGUse(Reg))
     return nullptr;
   MachineInstr *MI = MRI.getVRegDef(Reg);
   if (!MI)
     return nullptr;
+
+  if (!minmax &&
+      (MI->getOpcode() == RISCV::MAX || MI->getOpcode() == RISCV::MIN ||
+       MI->getOpcode() == RISCV::MINU || MI->getOpcode() == RISCV::MAXU))
+    return nullptr;
+
   // Check if MI can be predicated and folded into the CCMOV.
   if (getPredicatedOpcode(MI->getOpcode()) == RISCV::INSTRUCTION_LIST_END)
     return nullptr;
@@ -1809,11 +1816,12 @@ RISCVInstrInfo::optimizeSelect(MachineInstr &MI,
     return nullptr;
 
   MachineRegisterInfo &MRI = MI.getParent()->getParent()->getRegInfo();
-  MachineInstr *DefMI =
-      canFoldAsPredicatedOp(MI.getOperand(5).getReg(), MRI, this);
+  MachineInstr *DefMI = canFoldAsPredicatedOp(
+      MI.getOperand(5).getReg(), MRI, this, STI.hasShortForwardBranchIMinMax());
   bool Invert = !DefMI;
   if (!DefMI)
-    DefMI = canFoldAsPredicatedOp(MI.getOperand(4).getReg(), MRI, this);
+    DefMI = canFoldAsPredicatedOp(MI.getOperand(4).getReg(), MRI, this,
+                                  STI.hasShortForwardBranchIMinMax());
   if (!DefMI)
     return nullptr;