[dpdk-dev] [RFC] eal/arm: remove CASP constraints for GCC

[pbhagavatula at marvell.com]

From: Pavan Nikhilesh <pbhagavatula at marvell.com>

GCC now assigns even register pairs for CASP, the fix has also been
backported to all stable releases of older GCC versions.
Removing the manual register allocation allows GCC to inline the
functions and pick optimal registers for performing CASP.

Signed-off-by: Pavan Nikhilesh <pbhagavatula at marvell.com>
---
 lib/eal/arm/include/rte_atomic_64.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/lib/eal/arm/include/rte_atomic_64.h b/lib/eal/arm/include/rte_atomic_64.h
index fa6f334c0d..f6f31ae777 100644
--- a/lib/eal/arm/include/rte_atomic_64.h
+++ b/lib/eal/arm/include/rte_atomic_64.h
@@ -52,6 +52,7 @@ rte_atomic_thread_fence(int memorder)
 #define __LSE_PREAMBLE	""
 #endif
 
+#if defined(__clang__)
 #define __ATOMIC128_CAS_OP(cas_op_name, op_string)                          \
 static __rte_noinline void                                                  \
 cas_op_name(rte_int128_t *dst, rte_int128_t *old, rte_int128_t updated)     \
@@ -76,6 +77,19 @@ cas_op_name(rte_int128_t *dst, rte_int128_t *old, rte_int128_t updated)     \
 	old->val[0] = x0;                                                   \
 	old->val[1] = x1;                                                   \
 }
+#else
+#define __ATOMIC128_CAS_OP(cas_op_name, op_string)                          \
+static __rte_always_inline void                                             \
+cas_op_name(rte_int128_t *dst, rte_int128_t *old, rte_int128_t updated)     \
+{                                                                           \
+	asm volatile(                                                       \
+		__LSE_PREAMBLE                                              \
+		op_string " %[old], %H[old], %[upd], %H[upd], [%[dst]]"     \
+		: [old] "+r"(old->int128)                                   \
+		: [upd] "r"(updated.int128), [dst] "r"(dst)                 \
+		: "memory");                                                \
+}
+#endif
 
 __ATOMIC128_CAS_OP(__cas_128_relaxed, "casp")
 __ATOMIC128_CAS_OP(__cas_128_acquire, "caspa")
-- 
2.17.1