llvm · maryammo · Dec 12, 2025
diff --git a/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp b/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
@@ -3852,7 +3852,8 @@ bool PPCInstrInfo::convertToImmediateForm(MachineInstr &MI,
 
   // If this is not a reg+reg, but the DefMI is LI/LI8, check if its user MI
   // can be simpified to LI.
-  if (!HasImmForm && simplifyToLI(MI, *DefMI, ForwardingOperand, KilledDef))
+  if (!HasImmForm &&
+      simplifyToLI(MI, *DefMI, ForwardingOperand, KilledDef, &RegsToUpdate))
     return true;
 
   return false;
@@ -4619,7 +4620,8 @@ bool PPCInstrInfo::isImmElgibleForForwarding(const MachineOperand &ImmMO,
 
 bool PPCInstrInfo::simplifyToLI(MachineInstr &MI, MachineInstr &DefMI,
                                 unsigned OpNoForForwarding,
-                                MachineInstr **KilledDef) const {
+                                MachineInstr **KilledDef,
+                                SmallSet<Register, 4> *RegsToUpdate) const {
   if ((DefMI.getOpcode() != PPC::LI && DefMI.getOpcode() != PPC::LI8) ||
       !DefMI.getOperand(1).isImm())
     return false;
@@ -4687,6 +4689,11 @@ bool PPCInstrInfo::simplifyToLI(MachineInstr &MI, MachineInstr &DefMI,
           dbgs() << "Found LI -> CMPI -> ISEL, replacing with a copy.\n");
       LLVM_DEBUG(DefMI.dump(); MI.dump(); CompareUseMI.dump());
       LLVM_DEBUG(dbgs() << "Is converted to:\n");
+      if (RegsToUpdate) {
+        for (const MachineOperand &MO : CompareUseMI.operands())
+          if (MO.isReg())
+            RegsToUpdate->insert(MO.getReg());
+      }
       // Convert to copy and remove unneeded operands.
       CompareUseMI.setDesc(get(PPC::COPY));
       CompareUseMI.removeOperand(3);

diff --git a/llvm/lib/Target/PowerPC/PPCInstrInfo.h b/llvm/lib/Target/PowerPC/PPCInstrInfo.h
@@ -297,7 +297,8 @@ class PPCInstrInfo : public PPCGenInstrInfo {
   // Replace the instruction with single LI if possible. \p DefMI must be LI or
   // LI8.
   bool simplifyToLI(MachineInstr &MI, MachineInstr &DefMI,
-                    unsigned OpNoForForwarding, MachineInstr **KilledDef) const;
+                    unsigned OpNoForForwarding, MachineInstr **KilledDef,
+                    SmallSet<Register, 4> *RegsToUpdate = nullptr) const;
   // If the inst is imm-form and its register operand is produced by a ADDI, put
   // the imm into the inst directly and remove the ADDI if possible.
   bool transformToNewImmFormFedByAdd(MachineInstr &MI, MachineInstr &DefMI,

diff --git a/llvm/lib/Target/PowerPC/PPCMIPeephole.cpp b/llvm/lib/Target/PowerPC/PPCMIPeephole.cpp
@@ -731,6 +731,7 @@ bool PPCMIPeephole::simplifyCode() {
             LLVM_DEBUG(dbgs() << "Optimizing swap/swap => copy: ");
             LLVM_DEBUG(MI.dump());
             addRegToUpdate(MI.getOperand(1).getReg());
+
             BuildMI(MBB, &MI, MI.getDebugLoc(), TII->get(PPC::COPY),
                     MI.getOperand(0).getReg())
                 .add(DefMI->getOperand(1));
@@ -743,7 +744,19 @@ bool PPCMIPeephole::simplifyCode() {
                    DefOpc == PPC::XXPERMDIs &&
                    (DefMI->getOperand(2).getImm() == 0 ||
                     DefMI->getOperand(2).getImm() == 3)) {
-          ToErase = &MI;
+
+          bool OnlyUsedInMI = true;
+          for (MachineInstr &UseMI :
+               MRI->use_instructions(DefMI->getOperand(0).getReg())) {
+            if (UseMI.isDebugInstr())
+              continue;
+            if (&UseMI != &MI) {
+              OnlyUsedInMI = false;
+              break;
+            }
+          }
+          if (!OnlyUsedInMI)
+            break;
           Simplified = true;
           // Swap of a splat, convert to copy.
           if (Immed == 2) {
@@ -753,10 +766,12 @@ bool PPCMIPeephole::simplifyCode() {
                     MI.getOperand(0).getReg())
                 .add(MI.getOperand(1));
             addRegToUpdate(MI.getOperand(1).getReg());
+            ToErase = &MI;
             break;
           }
           // Splat fed by another splat - switch the output of the first
           // and remove the second.
+          ToErase = &MI;
           DefMI->getOperand(0).setReg(MI.getOperand(0).getReg());
           LLVM_DEBUG(dbgs() << "Removing redundant splat: ");
           LLVM_DEBUG(MI.dump());

diff --git a/llvm/test/CodeGen/PowerPC/peephole-livevars-tracking.mir b/llvm/test/CodeGen/PowerPC/peephole-livevars-tracking.mir
@@ -0,0 +1,83 @@
+# RUN: llc -verify-machineinstrs -mtriple=powerpc64le-unknown-linux  \
+# RUN:   -run-pass=ppc-mi-peepholes %s -o - | FileCheck %s
+
+# Test that peephole optimizations correctly update LiveVariables tracking.
+# XXPERMDI splat optimization skipped when splat register has multiple uses.
+# ISEL to COPY conversion tracks removed operand registers to prevent
+# LiveVariables corruption.
+
+---
+name: test_xxpermdi_splat_multiple_uses
+alignment: 16
+tracksRegLiveness: true
+registers:
+  - { id: 0, class: vrrc }
+  - { id: 28, class: vrrc }
+  - { id: 31, class: f8rc }
+  - { id: 34, class: vrrc }
+  - { id: 35, class: vrrc }
+body: |
+  bb.0:
+    liveins: $f1
+
+    %28:vrrc = XXLXORz
+    %31:f8rc = COPY $f1
+    %0:vrrc = XXPERMDIs %31, 0
+    %34:vrrc = XXPERMDI %28, %0, 3
+    %35:vrrc = XXPERMDI %0, %0, 3
+
+    ; CHECK-LABEL: name: test_xxpermdi_splat_multiple_uses
+    ; CHECK: %1:vrrc = XXLXORz
+    ; CHECK-NEXT: %2:f8rc = COPY killed $f1
+    ; CHECK-NEXT: %0:vrrc = XXPERMDIs killed %2, 0
+    ; CHECK-NEXT: %3:vrrc = XXPERMDI killed %1, %0, 3
+    ; CHECK-NEXT: %4:vrrc = XXPERMDI killed %0, %0, 3
+...
+---
+name: test_swap_isel_livevars
+alignment: 16
+tracksRegLiveness: true
+stack:
+  - { id: 0, size: 16, alignment: 16 }
+registers:
+  - { id: 2, class: vrrc }
+  - { id: 3, class: gprc_and_gprc_nor0 }
+  - { id: 4, class: gprc }
+  - { id: 7, class: gprc }
+  - { id: 8, class: gprc }
+  - { id: 21, class: vsrc }
+  - { id: 22, class: g8rc_and_g8rc_nox0 }
+  - { id: 25, class: vsrc }
+  - { id: 26, class: vsrc }
+  - { id: 29, class: crrc }
+  - { id: 31, class: vsrc }
+body: |
+  bb.0:
+    %7:gprc = LI 0
+    %8:gprc = LI 1
+    %21:vsrc = XXLXORz
+    %22:g8rc_and_g8rc_nox0 = ADDI8 %stack.0, 0
+    %29:crrc = CMPLWI %7, 0
+
+    STXVD2X %21, $zero8, %22 :: (store (s128) into %stack.0)
+    %25:vsrc = LXVD2X $zero8, %22 :: (load (s128) from %stack.0)
+    %26:vsrc = XXPERMDI %25, %25, 2
+    %2:vrrc = COPY %26
+    %31:vsrc = XXPERMDI %2, %2, 2
+    %3:gprc_and_gprc_nor0 = LI 0
+    %4:gprc = ISEL %3, %8, %29.sub_eq
+
+    ; CHECK-LABEL: name: test_swap_isel_livevars
+    ; CHECK: %3:gprc = LI 0
+    ; CHECK-NEXT: %4:gprc = LI 1
+    ; CHECK-NEXT: %5:vsrc = XXLXORz
+    ; CHECK-NEXT: %6:g8rc_and_g8rc_nox0 = ADDI8 %stack.0, 0
+    ; CHECK-NEXT: %9:crrc = CMPLWI killed %3, 0
+    ; CHECK-NEXT: STXVD2X killed %5, $zero8, %6
+    ; CHECK-NEXT: %7:vsrc = LXVD2X $zero8, killed %6
+    ; CHECK-NEXT: %8:vsrc = XXPERMDI %7, %7, 2
+    ; CHECK-NEXT: %0:vrrc = COPY killed %8
+    ; CHECK-NEXT: %10:vsrc = COPY killed %7
+    ; CHECK-NEXT: %1:gprc_and_gprc_nor0 = LI 0
+    ; CHECK-NEXT: %2:gprc = COPY killed %1
+...