Re: [RFC] Fix recent popcount change is breaking

[Kugan Vivekanandarajah]

On 10 July 2018 at 23:17, Richard Biener <richard.guent...@gmail.com> wrote:
> On Tue, Jul 10, 2018 at 3:06 PM Kugan Vivekanandarajah
> <kugan.vivekanandara...@linaro.org> wrote:
>>
>> 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?
>
> It doesn't work that way, all targets have this libfunc in libgcc.  This means
> the kernel has to provide it.  The only thing you could do is restrict
> replacement of CALL_EXPRs (in SCEV cprop) to those the target
> natively supports.

How about restricting it in expression_expensive_p ? Is that what you
wanted. Attached patch does this.
Bootstrap and regression testing progressing.

Thanks,
Kugan

>
> Richard.
>
>> 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/testsuite/gcc.target/aarch64/popcount4.c 
b/gcc/testsuite/gcc.target/aarch64/popcount4.c
index e69de29..ee55b2e 100644
--- a/gcc/testsuite/gcc.target/aarch64/popcount4.c
+++ b/gcc/testsuite/gcc.target/aarch64/popcount4.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized -mgeneral-regs-only" } */
+
+int PopCount (long b) {
+    int c = 0;
+
+    while (b) {
+       b &= b - 1;
+       c++;
+    }
+    return c;
+}
+
+/* { dg-final { scan-tree-dump-times "__builtin_popcount" 0 "optimized" } } */
diff --git a/gcc/tree-scalar-evolution.c b/gcc/tree-scalar-evolution.c
index 69122f2..ec8e4ec 100644
--- a/gcc/tree-scalar-evolution.c
+++ b/gcc/tree-scalar-evolution.c
@@ -257,7 +257,9 @@ 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 "optabs-query.h"
 #include "tree.h"
 #include "gimple.h"
 #include "ssa.h"
@@ -282,6 +284,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "gimple-fold.h"
 #include "tree-into-ssa.h"
 #include "builtins.h"
+#include "case-cfn-macros.h"
 
 static tree analyze_scalar_evolution_1 (struct loop *, tree);
 static tree analyze_scalar_evolution_for_address_of (struct loop *loop,
@@ -3500,6 +3503,23 @@ expression_expensive_p (tree expr)
     {
       tree arg;
       call_expr_arg_iterator iter;
+      tree fndecl = get_callee_fndecl (expr);
+
+      if (fndecl && DECL_BUILT_IN_CLASS (fndecl) == BUILT_IN_NORMAL)
+       {
+         combined_fn cfn = as_combined_fn (DECL_FUNCTION_CODE (fndecl));
+         switch (cfn)
+           {
+           CASE_CFN_POPCOUNT:
+             /* Check if opcode for popcount is available.  */
+             if (optab_handler (popcount_optab,
+                                TYPE_MODE (TREE_TYPE (CALL_EXPR_ARG (expr, 
0))))
+                 == CODE_FOR_nothing)
+               return true;
+           default:
+             break;
+           }
+       }
 
       if (!is_inexpensive_builtin (get_callee_fndecl (expr)))
        return true;