[dpdk-dev] [PATCH v2] lpm: fix build error on g++ with -O0 option

[Sangjin Han <sangjin@eecs.berkeley.edu>]

When rte_lpm.h is used on x86, -O0 option (no optimization at all)
given to gcc causes a compile error like this:

error: the last argument must be an 8-bit immediate
   i24 = _mm_srli_si128(i24, sizeof(uint64_t));

-O0 option is useful for debugging and code coverage measurement, but
this error prevents DPDK programs from building. This patch replaces
"sizeof(uint64_t)" with a constant literal "8" to work around the issue.
The issue occurs on gcc/g++ versions from 4.8 to 5.

Signed-off-by: Sangjin Han <sangjin@eecs.berkeley.edu>

---

v2:
* Added a comment
* Updated the commit message: both gcc and g++ are affected.
---
 lib/librte_lpm/rte_lpm_sse.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lib/librte_lpm/rte_lpm_sse.h b/lib/librte_lpm/rte_lpm_sse.h
index ef33c6a..7ab90b7 100644
--- a/lib/librte_lpm/rte_lpm_sse.h
+++ b/lib/librte_lpm/rte_lpm_sse.h
@@ -78,7 +78,9 @@ rte_lpm_lookupx4(const struct rte_lpm *lpm, xmm_t ip, uint32_t hop[4],
 
 	/* extract values from tbl24[] */
 	idx = _mm_cvtsi128_si64(i24);
-	i24 = _mm_srli_si128(i24, sizeof(uint64_t));
+
+  /* With -O0 option, gcc 4.8 - 5.4 fails to fold sizeof() into a constant */
+	i24 = _mm_srli_si128(i24, /* sizeof(uint64_t) */ 8);
 
 	ptbl = (const uint32_t *)&lpm->tbl24[(uint32_t)idx];
 	tbl[0] = *ptbl;
-- 
2.7.4