Index: llvm/lib/Target/WebAssembly/WebAssemblyFixBrTableDefaults.cpp
===================================================================
--- llvm/lib/Target/WebAssembly/WebAssemblyFixBrTableDefaults.cpp
+++ llvm/lib/Target/WebAssembly/WebAssemblyFixBrTableDefaults.cpp
@@ -61,9 +61,17 @@
   auto ExtMI = MF.getRegInfo().getVRegDef(MI.getOperand(0).getReg());
   if (ExtMI->getOpcode() == WebAssembly::I64_EXTEND_U_I32) {
     // Unnecessarily extending a 32-bit value to 64, remove it.
-    assert(MI.getOperand(0).getReg() == ExtMI->getOperand(0).getReg());
+    auto ExtDefReg = ExtMI->getOperand(0).getReg();
+    assert(MI.getOperand(0).getReg() == ExtDefReg);
     MI.getOperand(0).setReg(ExtMI->getOperand(1).getReg());
+    // Check if the br_table was the only user of the extend.
+    for (MachineInstr &UseMI : MF.getRegInfo().use_instructions(ExtDefReg)) {
+      if (&UseMI != &MI)
+        goto user_found;
+    }
+    // No more users of extend, delete it.
     ExtMI->eraseFromParent();
+    user_found:;
   } else {
     // Incoming 64-bit value that needs to be truncated.
     Register Reg32 =