[PowerPC][EarlyIfConversion] Do not insert isel if subtarget doesn't support isel (#72211)

Some subtargets of PPC don't support `isel` instruction, early-ifcvt
should not insert this instruction.

Author: Kai Luo

llvm/lib/Target/PowerPC/PPCInstrInfo.cpp

@@ -1530,6 +1530,9 @@ bool PPCInstrInfo::canInsertSelect(const MachineBasicBlock &MBB,
                                    Register DstReg, Register TrueReg,
                                    Register FalseReg, int &CondCycles,
                                    int &TrueCycles, int &FalseCycles) const {
+  if (!Subtarget.hasISEL())
+    return false;
+
   if (Cond.size() != 2)
     return false;
 

llvm/test/CodeGen/PowerPC/early-ifcvt-no-isel.mir

@@ -38,15 +38,21 @@ machineFunctionInfo: {}
 body:             |
   ; CHECK-LABEL: name: foo
   ; CHECK: bb.0.entry:
+  ; CHECK-NEXT:   successors: %bb.1, %bb.2
   ; CHECK-NEXT:   liveins: $x3
   ; CHECK-NEXT: {{  $}}
   ; CHECK-NEXT:   [[COPY:%[0-9]+]]:g8rc_and_g8rc_nox0 = COPY $x3
   ; CHECK-NEXT:   [[LWZ:%[0-9]+]]:gprc_and_gprc_nor0 = LWZ 0, [[COPY]] :: (load (s32) from %ir.dummy)
   ; CHECK-NEXT:   [[ADDI:%[0-9]+]]:gprc_and_gprc_nor0 = nsw ADDI [[LWZ]], 1
   ; CHECK-NEXT:   [[CMPWI:%[0-9]+]]:crrc = CMPWI [[LWZ]], 750
   ; CHECK-NEXT:   [[LI:%[0-9]+]]:gprc_and_gprc_nor0 = LI 1
-  ; CHECK-NEXT:   [[ISEL:%[0-9]+]]:gprc = ISEL [[ADDI]], [[LI]], [[CMPWI]].sub_lt
-  ; CHECK-NEXT:   STW killed [[ISEL]], 0, [[COPY]] :: (store (s32) into %ir.dummy)
+  ; CHECK-NEXT:   BCC 12, [[CMPWI]], %bb.2
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.1.entry:
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.2.entry:
+  ; CHECK-NEXT:   [[PHI:%[0-9]+]]:gprc = PHI [[LI]], %bb.1, [[ADDI]], %bb.0
+  ; CHECK-NEXT:   STW killed [[PHI]], 0, [[COPY]] :: (store (s32) into %ir.dummy)
   ; CHECK-NEXT:   [[LI8_:%[0-9]+]]:g8rc = LI8 0
   ; CHECK-NEXT:   $x3 = COPY [[LI8_]]
   ; CHECK-NEXT:   BLR8 implicit $lr8, implicit $rm, implicit $x3