Re: [PATCH] Check optab before transforming atomic bit test and operations

[Jeff Law via Gcc-patches]

On 11/15/2021 12:05 PM, H.J. Lu wrote:

On Mon, Nov 15, 2021 at 10:59 AM Jeff Law <jeffreya...@gmail.com> wrote:

On 11/15/2021 6:39 AM, H.J. Lu via Gcc-patches wrote:

Check optab before transforming equivalent, but slighly different cases
of atomic bit test and operations to their canonical forms.

gcc/

       PR middle-end/103184
       * tree-ssa-ccp.c (optimize_atomic_bit_test_and): Check optab
       before transforming equivalent, but slighly different cases to
       their canonical forms.

gcc/testsuite/

       PR middle-end/103184
       * gcc.dg/pr103184-1.c: New test.
       * gcc.dg/pr103184-2.c: Likewise.
       }
       }

-  switch (fn)
-    {
-    case IFN_ATOMIC_BIT_TEST_AND_SET:
-      optab = atomic_bit_test_and_set_optab;
-      break;
-    case IFN_ATOMIC_BIT_TEST_AND_COMPLEMENT:
-      optab = atomic_bit_test_and_complement_optab;
-      break;
-    case IFN_ATOMIC_BIT_TEST_AND_RESET:
-      optab = atomic_bit_test_and_reset_optab;
-      break;
-    default:
-      return;
-    }
-
     if (optab_handler (optab, TYPE_MODE (TREE_TYPE (lhs))) == CODE_FOR_nothing)
       return;

Shouldn't the test of the return value of optab_handler here just go
away since we're testing it earlier?  OK with that fix.

The earlier check is predicated on if (rhs_code != BIT_AND_EXPR):

   if (rhs_code != BIT_AND_EXPR)
     {
       if (rhs_code != NOP_EXPR && rhs_code != BIT_NOT_EXPR)
         return;

       tree use_lhs = gimple_assign_lhs (use_stmt);
       if (TREE_CODE (use_lhs) == SSA_NAME
           && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (use_lhs))
         return;

       tree use_rhs = gimple_assign_rhs1 (use_stmt);
       if (lhs != use_rhs)
         return;

       if (optab_handler (optab, TYPE_MODE (TREE_TYPE (lhs)))
           == CODE_FOR_nothing)
         return;

I can add an "else"

else  if (optab_handler (optab, TYPE_MODE (TREE_TYPE (lhs)))
             == CODE_FOR_nothing)
     return;

Will it be OK?

Sure.  THanks.
jeff