[RISCV] Clear kill flags after replaceRegWith in RISCVFoldMemOffset. (#136762)

Any kill flags that were present for the old register are not valid for
the replacement and the replacement may have extended the live range of
the replacement register.

Author: topperc

Diff for: llvm/lib/Target/RISCV/RISCVFoldMemOffset.cpp

@@ -274,6 +274,7 @@ bool RISCVFoldMemOffset::runOnMachineFunction(MachineFunction &MF) {
         MemMI->getOperand(2).setImm(NewOffset);
 
       MRI.replaceRegWith(MI.getOperand(0).getReg(), MI.getOperand(1).getReg());
+      MRI.clearKillFlags(MI.getOperand(1).getReg());
       MI.eraseFromParent();
     }
   }

Diff for: llvm/test/CodeGen/RISCV/fold-mem-offset.mir

@@ -0,0 +1,43 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 5
+# RUN: llc %s -mtriple=riscv32 -run-pass=riscv-fold-mem-offset -verify-machineinstrs -o - | FileCheck %s
+
+---
+name:            crash
+tracksRegLiveness: true
+noPhis:          false
+isSSA:           true
+noVRegs:         false
+hasFakeUses:     false
+body:             |
+  bb.0:
+    liveins: $x10, $x11
+
+    ; CHECK-LABEL: name: crash
+    ; CHECK: liveins: $x10, $x11
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:gpr = COPY $x11
+    ; CHECK-NEXT: [[COPY1:%[0-9]+]]:gpr = COPY $x10
+    ; CHECK-NEXT: [[SLLI:%[0-9]+]]:gpr = SLLI [[COPY]], 3
+    ; CHECK-NEXT: [[ADD:%[0-9]+]]:gpr = ADD killed [[SLLI]], [[COPY1]]
+    ; CHECK-NEXT: [[LUI:%[0-9]+]]:gpr = LUI 23
+    ; CHECK-NEXT: [[ADD1:%[0-9]+]]:gpr = ADD [[ADD]], [[LUI]]
+    ; CHECK-NEXT: [[ADD2:%[0-9]+]]:gpr = ADD [[ADD]], [[LUI]]
+    ; CHECK-NEXT: [[LW:%[0-9]+]]:gpr = LW killed [[ADD2]], 1792
+    ; CHECK-NEXT: [[LW1:%[0-9]+]]:gpr = LW killed [[ADD1]], 1796
+    ; CHECK-NEXT: $x10 = COPY [[LW]]
+    ; CHECK-NEXT: $x11 = COPY [[LW1]]
+    ; CHECK-NEXT: PseudoRET implicit $x10, implicit $x11
+    %1:gpr = COPY $x11
+    %0:gpr = COPY $x10
+    %3:gpr = SLLI %1, 3
+    %4:gpr = ADD killed %3, %0
+    %5:gpr = LUI 23
+    %6:gpr = ADDI %5, 1792
+    %7:gpr = ADD %4, killed %6
+    %8:gpr = ADD %4, %5
+    %9:gpr = LW killed %8, 1792
+    %10:gpr = LW killed %7, 4
+    $x10 = COPY %9
+    $x11 = COPY %10
+    PseudoRET implicit $x10, implicit $x11
+...