[WebAssembly] Fix fixBrTableIndex removing instruction without checking uses

Fixes: https://bugs.llvm.org/show_bug.cgi?id=52352
Differential Revision: https://reviews.llvm.org/D113230

Author: aardappel

llvm/lib/Target/WebAssembly/WebAssemblyFixBrTableDefaults.cpp

@@ -61,9 +61,13 @@ void fixBrTableIndex(MachineInstr &MI, MachineBasicBlock *MBB,
   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());
-    ExtMI->eraseFromParent();
+    if (MF.getRegInfo().use_nodbg_empty(ExtDefReg)) {
+      // No more users of extend, delete it.
+      ExtMI->eraseFromParent();
+    }
   } else {
     // Incoming 64-bit value that needs to be truncated.
     Register Reg32 =