[RFC] Fix recent popcount change is breaking

[Kugan Vivekanandarajah]

Hi,

Jeff told me that the recent popcount built-in detection is causing
kernel build issues as
ERROR: "__popcountsi2"
[drivers/net/wireless/broadcom/brcm80211/brcmfmac/brcmfmac.ko] undefined!

I could also reproduce this. AFIK, we should check if the libfunc is
defined while checking popcount?

I am testing the attached RFC patch. Is this reasonable?

Thanks,
Kugan

gcc/ChangeLog:

2018-07-10  Kugan Vivekanandarajah  <kug...@linaro.org>

    * tree-ssa-loop-niter.c (number_of_iterations_popcount): Check
    if libfunc for popcount is available.

diff --git a/gcc/tree-ssa-loop-niter.c b/gcc/tree-ssa-loop-niter.c
index f6fa2f7..2e2b9c6 100644
--- a/gcc/tree-ssa-loop-niter.c
+++ b/gcc/tree-ssa-loop-niter.c
@@ -21,6 +21,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "system.h"
 #include "coretypes.h"
 #include "backend.h"
+#include "target.h"
 #include "rtl.h"
 #include "tree.h"
 #include "gimple.h"
@@ -42,6 +43,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "tree-chrec.h"
 #include "tree-scalar-evolution.h"
 #include "params.h"
+#include "optabs-libfuncs.h"
 #include "tree-dfa.h"
 
 
@@ -2570,6 +2572,10 @@ number_of_iterations_popcount (loop_p loop, edge exit,
           (long_long_integer_type_node))
     fn = builtin_decl_implicit (BUILT_IN_POPCOUNTLL);
 
+  /* Check if libfunc for popcount is available.  */
+  if (!optab_libfunc (popcount_optab,
+                     TYPE_MODE (TREE_TYPE (src))))
+    return false;
   /* ??? Support promoting char/short to int.  */
   if (!fn)
     return false;