fixup! handle phi loop

Author: michaelmaitland

llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp

@@ -1323,6 +1323,7 @@ std::optional<MachineOperand>
 RISCVVLOptimizer::checkUsers(const MachineInstr &MI) const {
   std::optional<MachineOperand> CommonVL;
   SmallSetVector<MachineOperand *, 8> Worklist;
+  SmallPtrSet<const MachineInstr *, 4> PHISeen;
   for (auto &UserOp : MRI->use_operands(MI.getOperand(0).getReg()))
     Worklist.insert(&UserOp);
 
@@ -1340,7 +1341,7 @@ RISCVVLOptimizer::checkUsers(const MachineInstr &MI) const {
       continue;
     }
 
-    if (UserMI.isPHI()) {
+    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()))
         Worklist.insert(&PhiUse);

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

@@ -452,3 +452,27 @@ body: |
     %y:vr = PHI %w, %bb.0, %x, %bb.1
     %z:vr = PseudoVADD_VV_M1 $noreg, %y, $noreg, 1, 3 /* e8 */, 0 /* tu, mu */
 ...
+---
+name: phi_cycle
+tracksRegLiveness: true
+body: |
+  ; CHECK-LABEL: name: phi_cycle
+  ; 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: {{  $}}
+  ; CHECK-NEXT: bb.1:
+  ; CHECK-NEXT:   successors: %bb.1(0x80000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   %y:vr = PHI %x, %bb.0, %y, %bb.1
+  ; CHECK-NEXT:   %z:vr = PseudoVADD_VV_M1 $noreg, %y, $noreg, 1, 3 /* e8 */, 0 /* tu, mu */
+  ; CHECK-NEXT:   PseudoBR %bb.1
+  bb.0:
+    %x:vr = PseudoVADD_VV_M1 $noreg, $noreg, $noreg, -1, 3 /* e8 */, 0 /* tu, mu */
+  bb.1:
+    %y:vr = PHI %x, %bb.0, %y, %bb.1
+    %z:vr = PseudoVADD_VV_M1 $noreg, %y, $noreg, 1, 3 /* e8 */, 0 /* tu, mu */
+    PseudoBR %bb.1
+...
+

patch.diff

@@ -0,0 +1,21 @@
+commit d6462da5dde7d38604bd5783e609ec8392eaf74c
+Author: Michael Maitland <[email protected]>
+Date:   Thu Mar 20 08:21:12 2025 -0700
+
+    fixup! clang-format
+
+diff --git a/llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp b/llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp
+index 61f43e2e72b1..80ae0fd3d930 100644
+--- a/llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp
++++ b/llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp
+@@ -1342,8 +1342,8 @@ RISCVVLOptimizer::checkUsers(const MachineInstr &MI) const {
+ 
+     if (UserMI.isPHI()) {
+       LLVM_DEBUG(dbgs() << "    Peeking through uses of PHI\n");
+-        for (auto &PhiUse : MRI->use_operands(UserMI.getOperand(0).getReg()))
+-          Worklist.insert(&PhiUse);
++      for (auto &PhiUse : MRI->use_operands(UserMI.getOperand(0).getReg()))
++        Worklist.insert(&PhiUse);
+       continue;
+     }
+