diff --git a/llvm/lib/CodeGen/RegisterCoalescer.cpp b/llvm/lib/CodeGen/RegisterCoalescer.cpp
index cbb1a74049fbd7..7e9c992031f8d3 100644
--- a/llvm/lib/CodeGen/RegisterCoalescer.cpp
+++ b/llvm/lib/CodeGen/RegisterCoalescer.cpp
@@ -236,7 +236,8 @@ namespace {
     /// was successfully coalesced away. If it is not currently possible to
     /// coalesce this interval, but it may be possible if other things get
     /// coalesced, then it returns true by reference in 'Again'.
-    bool joinCopy(MachineInstr *CopyMI, bool &Again);
+    bool joinCopy(MachineInstr *CopyMI, bool &Again,
+                  SmallPtrSetImpl<MachineInstr *> &CurrentErasedInstrs);
 
     /// Attempt to join these two intervals.  On failure, this
     /// returns false.  The output "SrcInt" will not have been modified, so we
@@ -1964,7 +1965,9 @@ void RegisterCoalescer::setUndefOnPrunedSubRegUses(LiveInterval &LI,
   LIS->shrinkToUses(&LI);
 }
 
-bool RegisterCoalescer::joinCopy(MachineInstr *CopyMI, bool &Again) {
+bool RegisterCoalescer::joinCopy(
+    MachineInstr *CopyMI, bool &Again,
+    SmallPtrSetImpl<MachineInstr *> &CurrentErasedInstrs) {
   Again = false;
   LLVM_DEBUG(dbgs() << LIS->getInstructionIndex(*CopyMI) << '\t' << *CopyMI);
 
@@ -2156,7 +2159,9 @@ bool RegisterCoalescer::joinCopy(MachineInstr *CopyMI, bool &Again) {
   // CopyMI has been erased by joinIntervals at this point. Remove it from
   // ErasedInstrs since copyCoalesceWorkList() won't add a successful join back
   // to the work list. This keeps ErasedInstrs from growing needlessly.
-  ErasedInstrs.erase(CopyMI);
+  if (ErasedInstrs.erase(CopyMI))
+    // But we may encounter the instruction again in this iteration.
+    CurrentErasedInstrs.insert(CopyMI);
 
   // Rewrite all SrcReg operands to DstReg.
   // Also update DstReg operands to include DstIdx if it is set.
@@ -3982,21 +3987,33 @@ void RegisterCoalescer::lateLiveIntervalUpdate() {
 bool RegisterCoalescer::
 copyCoalesceWorkList(MutableArrayRef<MachineInstr*> CurrList) {
   bool Progress = false;
+  SmallPtrSet<MachineInstr *, 4> CurrentErasedInstrs;
   for (MachineInstr *&MI : CurrList) {
     if (!MI)
       continue;
     // Skip instruction pointers that have already been erased, for example by
     // dead code elimination.
-    if (ErasedInstrs.count(MI)) {
+    if (ErasedInstrs.count(MI) || CurrentErasedInstrs.count(MI)) {
       MI = nullptr;
       continue;
     }
     bool Again = false;
-    bool Success = joinCopy(MI, Again);
+    bool Success = joinCopy(MI, Again, CurrentErasedInstrs);
     Progress |= Success;
     if (Success || !Again)
       MI = nullptr;
   }
+  // Clear instructions not recorded in `ErasedInstrs` but erased.
+  if (!CurrentErasedInstrs.empty()) {
+    for (MachineInstr *&MI : CurrList) {
+      if (MI && CurrentErasedInstrs.count(MI))
+        MI = nullptr;
+    }
+    for (MachineInstr *&MI : WorkList) {
+      if (MI && CurrentErasedInstrs.count(MI))
+        MI = nullptr;
+    }
+  }
   return Progress;
 }
 
diff --git a/llvm/test/CodeGen/LoongArch/register-coalescer-crash-pr79718.mir b/llvm/test/CodeGen/LoongArch/register-coalescer-crash-pr79718.mir
new file mode 100644
index 00000000000000..9bbb579b762e63
--- /dev/null
+++ b/llvm/test/CodeGen/LoongArch/register-coalescer-crash-pr79718.mir
@@ -0,0 +1,213 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 4
+# RUN: llc -o - %s -mtriple=loongarch64 \
+# RUN:  -run-pass=register-coalescer -join-liveintervals=1 -join-splitedges=0 | FileCheck %s
+
+---
+name:            foo
+tracksRegLiveness: true
+body:             |
+  ; CHECK-LABEL: name: foo
+  ; CHECK: bb.0:
+  ; CHECK-NEXT:   successors: %bb.1(0x80000000)
+  ; CHECK-NEXT:   liveins: $r4, $r5, $r6, $r7, $r8
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   [[COPY:%[0-9]+]]:gpr = COPY $r8
+  ; CHECK-NEXT:   [[COPY1:%[0-9]+]]:gpr = COPY $r7
+  ; CHECK-NEXT:   [[COPY2:%[0-9]+]]:gpr = COPY $r6
+  ; CHECK-NEXT:   [[COPY3:%[0-9]+]]:gpr = COPY $r5
+  ; CHECK-NEXT:   [[COPY4:%[0-9]+]]:gpr = COPY $r4
+  ; CHECK-NEXT:   [[ANDI:%[0-9]+]]:gpr = ANDI [[COPY3]], 1
+  ; CHECK-NEXT:   [[ORI:%[0-9]+]]:gpr = ORI $r0, 1
+  ; CHECK-NEXT:   [[ANDI1:%[0-9]+]]:gpr = ANDI [[COPY2]], 1
+  ; CHECK-NEXT:   [[ANDI2:%[0-9]+]]:gpr = ANDI [[COPY1]], 1
+  ; CHECK-NEXT:   [[ANDI3:%[0-9]+]]:gpr = ANDI [[COPY]], 1
+  ; CHECK-NEXT:   [[COPY5:%[0-9]+]]:gpr = COPY $r0
+  ; CHECK-NEXT:   [[COPY6:%[0-9]+]]:gpr = COPY $r0
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.1:
+  ; CHECK-NEXT:   successors: %bb.2(0x80000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   [[COPY7:%[0-9]+]]:gpr = COPY [[COPY5]]
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.2:
+  ; CHECK-NEXT:   successors: %bb.3(0x40000000), %bb.4(0x40000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   BEQZ [[ANDI]], %bb.4
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.3:
+  ; CHECK-NEXT:   successors: %bb.9(0x80000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   PseudoBR %bb.9
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.4:
+  ; CHECK-NEXT:   successors: %bb.5(0x80000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.5:
+  ; CHECK-NEXT:   successors: %bb.7(0x7c000000), %bb.6(0x04000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   dead [[LD_D:%[0-9]+]]:gpr = LD_D $r0, 8
+  ; CHECK-NEXT:   dead [[LD_D1:%[0-9]+]]:gpr = LD_D $r0, 0
+  ; CHECK-NEXT:   BNEZ [[ANDI1]], %bb.7
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.6:
+  ; CHECK-NEXT:   successors: %bb.11(0x80000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   [[COPY6:%[0-9]+]]:gpr = COPY $r0
+  ; CHECK-NEXT:   PseudoBR %bb.11
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.7:
+  ; CHECK-NEXT:   successors: %bb.8(0x7c000000), %bb.10(0x04000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   BEQZ [[ANDI2]], %bb.10
+  ; CHECK-NEXT:   PseudoBR %bb.8
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.8:
+  ; CHECK-NEXT:   successors: %bb.9(0x04000000), %bb.5(0x7c000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   [[COPY6:%[0-9]+]]:gpr = ADDI_D [[COPY6]], 1
+  ; CHECK-NEXT:   BEQZ [[ANDI3]], %bb.5
+  ; CHECK-NEXT:   PseudoBR %bb.9
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.9:
+  ; CHECK-NEXT:   successors: %bb.12(0x80000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   ST_B $r0, [[COPY4]], 0
+  ; CHECK-NEXT:   PseudoBR %bb.12
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.10:
+  ; CHECK-NEXT:   successors: %bb.11(0x80000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   [[COPY5:%[0-9]+]]:gpr = ADDI_D [[COPY6]], 1
+  ; CHECK-NEXT:   [[COPY6:%[0-9]+]]:gpr = COPY [[ORI]]
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.11:
+  ; CHECK-NEXT:   successors: %bb.12(0x80000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   ST_D $r0, [[COPY4]], 0
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.12:
+  ; CHECK-NEXT:   successors: %bb.2(0x7c000000), %bb.1(0x04000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   BEQ [[COPY7]], [[ORI]], %bb.2
+  ; CHECK-NEXT:   PseudoBR %bb.1
+  bb.0:
+    liveins: $r4, $r5, $r6, $r7, $r8
+
+    %0:gpr = COPY killed $r8
+    %1:gpr = COPY killed $r7
+    %2:gpr = COPY killed $r6
+    %3:gpr = COPY killed $r5
+    %4:gpr = COPY killed $r4
+    %5:gpr = COPY $r0
+    %6:gpr = COPY killed %5
+    %7:gpr = ANDI killed %3, 1
+    %8:gpr = ORI $r0, 1
+    %9:gpr = ANDI killed %2, 1
+    %10:gpr = ANDI killed %1, 1
+    %11:gpr = ANDI killed %0, 1
+    %12:gpr = COPY %6
+    %13:gpr = COPY killed %6
+    %14:gpr = IMPLICIT_DEF
+
+  bb.1:
+    %15:gpr = COPY killed %14
+    %16:gpr = COPY killed %13
+    %17:gpr = COPY killed %12
+    %18:gpr = COPY %17
+    %19:gpr = COPY %16
+    %20:gpr = COPY killed %16
+    %21:gpr = COPY killed %15
+
+  bb.2:
+    successors: %bb.3, %bb.4
+
+    %22:gpr = COPY killed %21
+    %23:gpr = COPY killed %20
+    %24:gpr = COPY killed %19
+    %25:gpr = COPY killed %18
+    BEQZ %7, %bb.4
+
+  bb.3:
+    %26:gpr = COPY killed %24
+    %27:gpr = COPY killed %23
+    PseudoBR %bb.9
+
+  bb.4:
+    %28:gpr = COPY killed %23
+
+  bb.5:
+    successors: %bb.7(0x7c000000), %bb.6(0x04000000)
+
+    %29:gpr = COPY killed %28
+    dead %30:gpr = LD_D $r0, 8
+    dead %31:gpr = LD_D $r0, 0
+    BNEZ %9, %bb.7
+
+  bb.6:
+    %32:gpr = COPY $r0
+    %33:gpr = COPY killed %32
+    %34:gpr = COPY killed %33
+    %35:gpr = COPY killed %22
+    PseudoBR %bb.11
+
+  bb.7:
+    successors: %bb.8(0x7c000000), %bb.10(0x04000000)
+
+    BEQZ %10, %bb.10
+    PseudoBR %bb.8
+
+  bb.8:
+    successors: %bb.9(0x04000000), %bb.5(0x7c000000)
+
+    %36:gpr = ADDI_D killed %29, 1
+    %28:gpr = COPY %36
+    %26:gpr = COPY %36
+    %27:gpr = COPY killed %36
+    BEQZ %11, %bb.5
+    PseudoBR %bb.9
+
+  bb.9:
+    %37:gpr = COPY killed %27
+    %38:gpr = COPY killed %26
+    %39:gpr = COPY $r0
+    ST_B killed %39, %4, 0
+    %40:gpr = COPY killed %25
+    %41:gpr = COPY killed %38
+    %42:gpr = COPY killed %37
+    %43:gpr = COPY killed %22
+    PseudoBR %bb.12
+
+  bb.10:
+    %44:gpr = ADDI_D killed %29, 1
+    %34:gpr = COPY %8
+    %35:gpr = COPY killed %44
+
+  bb.11:
+    %45:gpr = COPY killed %35
+    %46:gpr = COPY killed %34
+    %47:gpr = COPY $r0
+    ST_D killed %47, %4, 0
+    %40:gpr = COPY %45
+    %41:gpr = COPY %46
+    %42:gpr = COPY killed %46
+    %43:gpr = COPY killed %45
+
+  bb.12:
+    successors: %bb.2(0x7c000000), %bb.1(0x04000000)
+
+    %48:gpr = COPY killed %43
+    %49:gpr = COPY killed %42
+    %50:gpr = COPY killed %41
+    %51:gpr = COPY killed %40
+    %12:gpr = COPY %51
+    %13:gpr = COPY %50
+    %14:gpr = COPY %48
+    %18:gpr = COPY killed %51
+    %19:gpr = COPY killed %50
+    %20:gpr = COPY killed %49
+    %21:gpr = COPY killed %48
+    BEQ %17, %8, %bb.2
+    PseudoBR %bb.1
+
+...
diff --git a/llvm/test/CodeGen/X86/PR71178-register-coalescer-crash.ll b/llvm/test/CodeGen/X86/PR71178-register-coalescer-crash.ll
new file mode 100644
index 00000000000000..0ce346f7c2e02c
--- /dev/null
+++ b/llvm/test/CodeGen/X86/PR71178-register-coalescer-crash.ll
@@ -0,0 +1,103 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 4
+; RUN: llc < %s -mtriple=x86_64 -- | FileCheck %s
+
+define i32 @h(i1 %arg, i32 %arg1) {
+; CHECK-LABEL: h:
+; CHECK:       # %bb.0: # %bb
+; CHECK-NEXT:    movl $1, %eax
+; CHECK-NEXT:    movabsq $9166129423, %rcx # imm = 0x22258090F
+; CHECK-NEXT:    xorl %edx, %edx
+; CHECK-NEXT:    jmp .LBB0_1
+; CHECK-NEXT:    .p2align 4, 0x90
+; CHECK-NEXT:  .LBB0_9: # %bb18
+; CHECK-NEXT:    # in Loop: Header=BB0_1 Depth=1
+; CHECK-NEXT:    xorl %eax, %eax
+; CHECK-NEXT:    testb $1, %dil
+; CHECK-NEXT:    jne .LBB0_10
+; CHECK-NEXT:  .LBB0_1: # %bb4
+; CHECK-NEXT:    # =>This Inner Loop Header: Depth=1
+; CHECK-NEXT:    testq %rdx, %rdx
+; CHECK-NEXT:    jne .LBB0_2
+; CHECK-NEXT:  # %bb.7: # %bb16
+; CHECK-NEXT:    # in Loop: Header=BB0_1 Depth=1
+; CHECK-NEXT:    testb $1, %dil
+; CHECK-NEXT:    jne .LBB0_9
+; CHECK-NEXT:  # %bb.8: # %bb17
+; CHECK-NEXT:    # in Loop: Header=BB0_1 Depth=1
+; CHECK-NEXT:    movq %rcx, %rdx
+; CHECK-NEXT:    jmp .LBB0_9
+; CHECK-NEXT:  .LBB0_2: # %bb9
+; CHECK-NEXT:    # in Loop: Header=BB0_1 Depth=1
+; CHECK-NEXT:    testb $1, %dil
+; CHECK-NEXT:    testb $1, %dil
+; CHECK-NEXT:    je .LBB0_4
+; CHECK-NEXT:  # %bb.3: # %bb13
+; CHECK-NEXT:    # in Loop: Header=BB0_1 Depth=1
+; CHECK-NEXT:    xorl %eax, %eax
+; CHECK-NEXT:  .LBB0_4: # %bb14
+; CHECK-NEXT:    # in Loop: Header=BB0_1 Depth=1
+; CHECK-NEXT:    cmpl $1, %esi
+; CHECK-NEXT:    je .LBB0_1
+; CHECK-NEXT:  # %bb.5: # %bb14
+; CHECK-NEXT:    movl %eax, %r8d
+; CHECK-NEXT:    testl %esi, %esi
+; CHECK-NEXT:    movl %esi, %eax
+; CHECK-NEXT:    jne .LBB0_6
+; CHECK-NEXT:  .LBB0_10: # %bb22
+; CHECK-NEXT:    retq
+; CHECK-NEXT:  .LBB0_6: # %bb22.loopexit1
+; CHECK-NEXT:    movl %r8d, %eax
+; CHECK-NEXT:    retq
+bb:
+  br label %bb2
+
+bb2:                                              ; preds = %bb14, %bb
+  %i = phi i64 [ %i5, %bb14 ], [ 0, %bb ]
+  %i3 = phi i32 [ %i15, %bb14 ], [ 1, %bb ]
+  br label %bb4
+
+bb4:                                              ; preds = %bb18, %bb2
+  %i5 = phi i64 [ %i19, %bb18 ], [ %i, %bb2 ]
+  %i6 = phi i64 [ %i20, %bb18 ], [ %i, %bb2 ]
+  %i7 = phi i32 [ 0, %bb18 ], [ %i3, %bb2 ]
+  %i8 = icmp eq i64 %i6, 0
+  br i1 %i8, label %bb16, label %bb9
+
+bb9:                                              ; preds = %bb4
+  br i1 %arg, label %bb12, label %bb10
+
+bb10:                                             ; preds = %bb9
+  %i11 = sdiv i64 0, 0
+  br label %bb12
+
+bb12:                                             ; preds = %bb10, %bb9
+  br i1 %arg, label %bb13, label %bb14
+
+bb13:                                             ; preds = %bb12
+  br label %bb14
+
+bb14:                                             ; preds = %bb13, %bb12
+  %i15 = phi i32 [ 0, %bb13 ], [ %i7, %bb12 ]
+  switch i32 %arg1, label %bb22 [
+    i32 0, label %bb21
+    i32 1, label %bb2
+  ]
+
+bb16:                                             ; preds = %bb4
+  br i1 %arg, label %bb18, label %bb17
+
+bb17:                                             ; preds = %bb16
+  br label %bb18
+
+bb18:                                             ; preds = %bb17, %bb16
+  %i19 = phi i64 [ 9166129423, %bb17 ], [ %i5, %bb16 ]
+  %i20 = phi i64 [ 9166129423, %bb17 ], [ %i6, %bb16 ]
+  br i1 %arg, label %bb22, label %bb4
+
+bb21:                                             ; preds = %bb14
+  br label %bb22
+
+bb22:                                             ; preds = %bb21, %bb18, %bb14
+  %i23 = phi i32 [ %arg1, %bb21 ], [ %i15, %bb14 ], [ 0, %bb18 ]
+  ret i32 %i23
+}