perf: add TWOPASS_CN_PROC dispatch in nrLDPC_decoder

Add //#define TWOPASS_CN_PROC alongside UNROLL_CN_PROC=1.
When UNROLL_CN_PROC is commented out and TWOPASS_CN_PROC is
defined, all four cnProc call sites (first-iter BG1/BG2,
loop BG1/BG2) dispatch to nrLDPC_cnProc_BG1_2pass /
nrLDPC_cnProc_BG2_2pass instead of the LUT-based variants.

To benchmark: comment UNROLL_CN_PROC and uncomment TWOPASS_CN_PROC.
To revert to LUT generic: comment both.

Assisted-by: Claude:claude-sonnet-4.6
Signed-off-by: Raymond Knopp <raymond.knopp@eurecom.fr>

openair1/PHY/CODING/nrLDPC_decoder/nrLDPC_decoder.c

@@ -19,6 +19,7 @@
 #include "openair1/PHY/CODING/coding_defs.h"
 #include "log.h"
 #define UNROLL_CN_PROC 1
+//#define TWOPASS_CN_PROC   // comment UNROLL_CN_PROC and uncomment to use two-pass min-sum cnProc
 #define UNROLL_BN_PROC 1
 #define UNROLL_BN_PROC_PC 1
 #define UNROLL_BN2CN_PROC 1
@@ -237,8 +238,12 @@ static inline uint32_t nrLDPC_decoder_core(int8_t* p_llr,
     NR_LDPC_PROFILER_DETAIL(start_meas(&p_profiler->cnProc));
     if (BG==1) {
 #ifndef UNROLL_CN_PROC
+  #ifdef TWOPASS_CN_PROC
+      nrLDPC_cnProc_BG1_2pass(p_lut, cnProcBuf, cnProcBufRes, Z);
+  #else
       nrLDPC_cnProc_BG1(p_lut, cnProcBuf, cnProcBufRes, Z);
-#else        
+  #endif
+#else
         switch (R)
         {
             case 13:
@@ -281,7 +286,11 @@ static inline uint32_t nrLDPC_decoder_core(int8_t* p_llr,
 #endif        
     } else {
 #ifndef UNROLL_CN_PROC
+  #ifdef TWOPASS_CN_PROC
+        nrLDPC_cnProc_BG2_2pass(p_lut, cnProcBuf, cnProcBufRes, Z);
+  #else
         nrLDPC_cnProc_BG2(p_lut, cnProcBuf, cnProcBufRes, Z);
+  #endif
 #else
         switch (R) {
             case 15:
@@ -543,8 +552,12 @@ static inline uint32_t nrLDPC_decoder_core(int8_t* p_llr,
 #endif
         if (BG==1) {
 #ifndef UNROLL_CN_PROC
+  #ifdef TWOPASS_CN_PROC
+           nrLDPC_cnProc_BG1_2pass(p_lut, cnProcBuf, cnProcBufRes, Z);
+  #else
            nrLDPC_cnProc_BG1(p_lut, cnProcBuf, cnProcBufRes, Z);
-#else        
+  #endif
+#else
            switch (R) {
             case 13:
             {
@@ -583,7 +596,11 @@ static inline uint32_t nrLDPC_decoder_core(int8_t* p_llr,
 #endif        
         } else {
 #ifndef UNROLL_CN_PROC
+  #ifdef TWOPASS_CN_PROC
+           nrLDPC_cnProc_BG2_2pass(p_lut, cnProcBuf, cnProcBufRes, Z);
+  #else
            nrLDPC_cnProc_BG2(p_lut, cnProcBuf, cnProcBufRes, Z);
+  #endif
 #else
            switch (R) {
             case 15: