Add zero-idiom test

Author: rez5427

llvm/test/CodeGen/X86/regcoalesce-zeroidiom.ll

@@ -0,0 +1,15 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -mattr=+sse2 | FileCheck %s
+
+; Test that zero-idiom instructions (like xor %eax, %eax) are rematerialized
+; instead of being copied when used as return values. Rematerialization produces
+; independent zero-latency instructions which is better than copying.
+
+define { i64, i64 } @test_xor_int_two_returns() {
+; CHECK-LABEL: test_xor_int_two_returns:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    xorl %eax, %eax
+; CHECK-NEXT:    xorl %edx, %edx
+; CHECK-NEXT:    retq
+  ret { i64, i64 } { i64 0, i64 0 }
+}