From 915f25141a7c57b6a2a3bc8697572644af181ec5 Mon Sep 17 00:00:00 2001
From: Ben Barham <ben_barham@apple.com>
Date: Mon, 6 Jun 2022 10:45:27 -0700
Subject: [PATCH] Prevent unused but set variable warning

`_dispatch_preemption_yield(++spins)` has an expansion to
`(void)++spins`, but this isn't considered a use of `spins` in Clang.
Add a `(void)spins` to prevent an unused variable warning.

Resolves rdar://93596069.
---
 src/CMakeLists.txt | 3 ---
 src/shims/yield.c  | 5 +++++
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index c5412ce59..adc989d42 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -1,7 +1,4 @@
 
-# Remove once underlying clang warning is fixed (rdar://93596069)
-set_source_files_properties(shims/yield.c PROPERTIES COMPILE_FLAGS -Wno-error=unused-but-set-variable)
-
 if(NOT CMAKE_SYSTEM_NAME STREQUAL Darwin)
   add_subdirectory(BlocksRuntime)
 endif()
diff --git a/src/shims/yield.c b/src/shims/yield.c
index d0c5fff92..cf1f5cefd 100644
--- a/src/shims/yield.c
+++ b/src/shims/yield.c
@@ -25,6 +25,11 @@ static void *
 __DISPATCH_WAIT_FOR_ENQUEUER__(void **ptr)
 {
 	int spins = 0;
+        // Different platforms may expand `_dispatch_preemption_yield` to a
+        // no-op, but `(void)++spins` is not considered a use like
+        // `(void)spins` is. Add a use to avoid unused var warnings.
+        (void)spins;
+
 	void *value;
 	while ((value = os_atomic_load(ptr, relaxed)) == NULL) {
 		_dispatch_preemption_yield(++spins);