fixup! improve phi cycle logic

Author: michaelmaitland

llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp

@@ -1343,8 +1343,12 @@ RISCVVLOptimizer::checkUsers(const MachineInstr &MI) const {
 
     if (UserMI.isPHI() && PHISeen.insert(&UserMI).second) {
       LLVM_DEBUG(dbgs() << "    Peeking through uses of PHI\n");
-      for (auto &PhiUse : MRI->use_operands(UserMI.getOperand(0).getReg()))
+      for (auto &PhiUse : MRI->use_operands(UserMI.getOperand(0).getReg())) {
+        // If UserMI has a PHI cycle, don't analyze it.
+        if (PhiUse.getParent() == &UserMI)
+          continue;
         Worklist.insert(&PhiUse);
+      }
       continue;
     }
 

llvm/test/CodeGen/RISCV/rvv/vl-opt.mir

@@ -460,7 +460,7 @@ body: |
   ; CHECK: bb.0:
   ; CHECK-NEXT:   successors: %bb.1(0x80000000)
   ; CHECK-NEXT: {{  $}}
-  ; CHECK-NEXT:   %x:vr = PseudoVADD_VV_M1 $noreg, $noreg, $noreg, -1, 3 /* e8 */, 0 /* tu, mu */
+  ; CHECK-NEXT:   %x:vr = PseudoVADD_VV_M1 $noreg, $noreg, $noreg, 1, 3 /* e8 */, 0 /* tu, mu */
   ; CHECK-NEXT: {{  $}}
   ; CHECK-NEXT: bb.1:
   ; CHECK-NEXT:   successors: %bb.1(0x80000000)