+#!+compare-and-swap-vops
+(define-vop (%compare-and-swap-symbol-value)
+ (:translate %compare-and-swap-symbol-value)
+ (:args (symbol :scs (descriptor-reg))
+ (old :scs (descriptor-reg any-reg))
+ (new :scs (descriptor-reg any-reg)))
+ (:temporary (:sc non-descriptor-reg) temp)
+ (:results (result :scs (descriptor-reg any-reg) :from :load))
+ (:policy :fast-safe)
+ (:vop-var vop)
+ (:generator 15
+ (inst sync)
+ #!+sb-thread
+ (assemble ()
+ (loadw temp symbol symbol-tls-index-slot other-pointer-lowtag)
+ ;; Thread-local area, no synchronization needed.
+ (inst lwzx result thread-base-tn temp)
+ (inst cmpw result old)
+ (inst bne DONT-STORE-TLS)
+ (inst stwx new thread-base-tn temp)
+ DONT-STORE-TLS
+
+ (inst cmpwi result no-tls-value-marker-widetag)
+ (inst bne CHECK-UNBOUND))
+
+ (inst li temp (- (* symbol-value-slot n-word-bytes)
+ other-pointer-lowtag))
+ LOOP
+ (inst lwarx result symbol temp)
+ (inst cmpw result old)
+ (inst bne CHECK-UNBOUND)
+ (inst stwcx. new symbol temp)
+ (inst bne LOOP)
+
+ CHECK-UNBOUND
+ (inst isync)
+ (inst cmpwi result unbound-marker-widetag)
+ (inst beq (generate-error-code vop 'unbound-symbol-error symbol))))
+