fixup! CheerpWasmWriter - Support for atomics

llvm/lib/CheerpWriter/CheerpWasmWriter.cpp

@@ -3676,6 +3676,14 @@ bool CheerpWasmWriter::compileInlineInstruction(WasmBuffer& code, const Instruct
 				encodeInst(WasmThreadsU32U32Opcode::I64_ATOMIC_RMW_CMPXCHG, 0x3, offset, code);
 			else
 				llvm::report_fatal_error("Atomic cmpxchg only allowed on integers");
+			// Do not duplicate the result and render the comparison if this instruction has no uses.
+			// We do however have to push a garbage constant onto the stack, because
+			// compileInstructionAndSet will drop 2 times (since there are 2 registers for this).
+			if (I.use_empty())
+			{
+				encodeInst(WasmS32Opcode::I32_CONST, 0, code);
+				break;
+			}
 			// Now compile the second part of this two-register operation, the comparison between
 			// the original (loaded) value and the comparison value.
 			uint32_t idx = registerize.getRegisterId(&ai, 0, edgeContext);