atomic: Implement generic atom[ic]_xchg

Signed-off-by: Aaron Watry <awatry@gmail.com>
Reviewed-by: Tom Stellard <thomas.stellard@amd.com>
llvm-svn: 217917
diff --git a/libclc/generic/lib/atomic/atomic_impl.ll b/libclc/generic/lib/atomic/atomic_impl.ll
index 792762b2..b5495cc 100644
--- a/libclc/generic/lib/atomic/atomic_impl.ll
+++ b/libclc/generic/lib/atomic/atomic_impl.ll
@@ -94,6 +94,18 @@
   ret i32 %0
 }
 
+define i32 @__clc_atomic_xchg_addr1(i32 addrspace(1)* nocapture %ptr, i32 %value) nounwind alwaysinline {
+entry:
+  %0 = atomicrmw volatile xchg i32 addrspace(1)* %ptr, i32 %value seq_cst
+  ret i32 %0
+}
+
+define i32 @__clc_atomic_xchg_addr3(i32 addrspace(3)* nocapture %ptr, i32 %value) nounwind alwaysinline {
+entry:
+  %0 = atomicrmw volatile xchg i32 addrspace(3)* %ptr, i32 %value seq_cst
+  ret i32 %0
+}
+
 define i32 @__clc_atomic_xor_addr1(i32 addrspace(1)* nocapture %ptr, i32 %value) nounwind alwaysinline {
 entry:
   %0 = atomicrmw volatile xor i32 addrspace(1)* %ptr, i32 %value seq_cst