Improve __builtin_popcount* (x) == 1 generation if x is known != 0 [PR90693]

We expand __builtin_popcount* (x) == 1 as
x ^ (x - 1) > x - 1, either unconditionally in tree-ssa-math-opts.cc
if we don't have a direct optab support for popcount, or during
expansion where we compare the costs of comparison of the popcount
against one vs. the above expression.
As mentioned in the PR, if we know from ranger that the argument is
not zero, we can emit x & (x - 1) == 0 test which is same number of
GIMPLE statements, but on many targets cheaper (e.g. whenever an AND
instruction can also set flags on whether result was zero or not).

The following patch does that.

2024-01-05  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/90693
	* tree-ssa-math-opts.cc (match_single_bit_test): If
	tree_expr_nonzero_p (arg), remember it in the second argument to
	IFN_POPCOUNT or lower it as arg & (arg - 1) == 0 rather than
	arg ^ (arg - 1) > arg - 1.
	* internal-fn.cc (expand_POPCOUNT): If second argument to
	IFN_POPCOUNT suggests arg is non-zero, try to expand it as
	arg & (arg - 1) == 0 rather than arg ^ (arg - 1) > arg - 1.

	* gcc.target/i386/pr90693-2.c: New test.

diff --git a/gcc/internal-fn.cc b/gcc/internal-fn.cc
index 80efd2f89806042ea01866bf85efc0107ee17021..a07f25f3aee3de6056376412fdb3c3954f15fb03 100644 (file)
--- a/gcc/internal-fn.cc
+++ b/gcc/internal-fn.cc
@@ -5118,10 +5118,13 @@ expand_POPCOUNT (internal_fn fn, gcall *stmt)
   /* If .POPCOUNT call has 2 arguments, match_single_bit_test marked it
      because the result is only used in an equality comparison against 1.
      Use rtx costs in that case to determine if .POPCOUNT (arg) == 1
-     or (arg ^ (arg - 1)) > arg - 1 is cheaper.  */
+     or (arg ^ (arg - 1)) > arg - 1 is cheaper.
+     If .POPCOUNT second argument is 0, we additionally know that arg
+     is non-zero, so use arg & (arg - 1) == 0 instead.  */
   bool speed_p = optimize_insn_for_speed_p ();
   tree lhs = gimple_call_lhs (stmt);
   tree arg = gimple_call_arg (stmt, 0);
+  bool nonzero_arg = integer_zerop (gimple_call_arg (stmt, 1));
   tree type = TREE_TYPE (arg);
   machine_mode mode = TYPE_MODE (type);
   do_pending_stack_adjust ();
@@ -5147,11 +5150,15 @@ expand_POPCOUNT (internal_fn fn, gcall *stmt)
                                   1, OPTAB_DIRECT);
   if (argm1 == NULL_RTX)
     goto fail;
-  rtx argxorargm1 = expand_simple_binop (mode, XOR, op0, argm1, NULL_RTX,
-                                        1, OPTAB_DIRECT);
+  rtx argxorargm1 = expand_simple_binop (mode, nonzero_arg ? AND : XOR, op0,
+                                        argm1, NULL_RTX, 1, OPTAB_DIRECT);
   if (argxorargm1 == NULL_RTX)
     goto fail;
-  rtx cmp = emit_store_flag (NULL_RTX, GTU, argxorargm1, argm1, mode, 1, 1);
+  rtx cmp;
+  if (nonzero_arg)
+    cmp = emit_store_flag (NULL_RTX, EQ, argxorargm1, const0_rtx, mode, 1, 1);
+  else
+    cmp = emit_store_flag (NULL_RTX, GTU, argxorargm1, argm1, mode, 1, 1);
   if (cmp == NULL_RTX)
     goto fail;
   rtx_insn *cmp_insns = get_insns ();

diff --git a/gcc/testsuite/gcc.target/i386/pr90693-2.c b/gcc/testsuite/gcc.target/i386/pr90693-2.c
new file mode 100644 (file)
index 0000000..3cfeccb
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr90693-2.c
@@ -0,0 +1,33 @@
+/* PR tree-optimization/90693 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -mno-abm -mno-popcnt -fdump-tree-optimized" } */
+/* { dg-final { scan-tree-dump-not "POPCOUNT \\\(" "optimized" } } */
+/* { dg-final { scan-tree-dump-not "__builtin_popcount(ll)? \\\(" "optimized" } } */
+
+int
+foo (unsigned int x)
+{
+  if (x == 0)
+    __builtin_unreachable ();
+  return __builtin_popcount (x) == 1;
+}
+
+int
+bar (unsigned int x)
+{
+  return (x & (x - 1)) == 0;
+}
+
+int
+baz (unsigned long long x)
+{
+  if (x == 0)
+    __builtin_unreachable ();
+  return __builtin_popcountll (x) == 1;
+}
+
+int
+qux (unsigned long long x)
+{
+  return (x & (x - 1)) == 0;
+}

diff --git a/gcc/tree-ssa-math-opts.cc b/gcc/tree-ssa-math-opts.cc
index 05d3b92d97422087a7ac6b35605bf56aa3c15710..2db26e4ed4868aa1baf2fa88a0f327f0bd4ea56f 100644 (file)
--- a/gcc/tree-ssa-math-opts.cc
+++ b/gcc/tree-ssa-math-opts.cc
@@ -5194,12 +5194,14 @@ match_single_bit_test (gimple_stmt_iterator *gsi, gimple *stmt)
   tree type = TREE_TYPE (arg);
   if (!INTEGRAL_TYPE_P (type))
     return;
+  bool nonzero_arg = tree_expr_nonzero_p (arg);
   if (direct_internal_fn_supported_p (IFN_POPCOUNT, type, OPTIMIZE_FOR_BOTH))
     {
       /* Tell expand_POPCOUNT the popcount result is only used in equality
         comparison with one, so that it can decide based on rtx costs.  */
       gimple *g = gimple_build_call_internal (IFN_POPCOUNT, 2, arg,
-                                             integer_one_node);
+                                             nonzero_arg ? integer_zero_node
+                                             : integer_one_node);
       gimple_call_set_lhs (g, gimple_call_lhs (call));
       gimple_stmt_iterator gsi2 = gsi_for_stmt (call);
       gsi_replace (&gsi2, g, true);
@@ -5209,19 +5211,29 @@ match_single_bit_test (gimple_stmt_iterator *gsi, gimple *stmt)
   gimple *g = gimple_build_assign (argm1, PLUS_EXPR, arg,
                                   build_int_cst (type, -1));
   gsi_insert_before (gsi, g, GSI_SAME_STMT);
-  g = gimple_build_assign (make_ssa_name (type), BIT_XOR_EXPR, arg, argm1);
+  g = gimple_build_assign (make_ssa_name (type),
+                          nonzero_arg ? BIT_AND_EXPR : BIT_XOR_EXPR,
+                          arg, argm1);
   gsi_insert_before (gsi, g, GSI_SAME_STMT);
+  tree_code cmpcode;
+  if (nonzero_arg)
+    {
+      argm1 = build_zero_cst (type);
+      cmpcode = code;
+    }
+  else
+    cmpcode = code == EQ_EXPR ? GT_EXPR : LE_EXPR;
   if (gcond *cond = dyn_cast <gcond *> (stmt))
     {
       gimple_cond_set_lhs (cond, gimple_assign_lhs (g));
       gimple_cond_set_rhs (cond, argm1);
-      gimple_cond_set_code (cond, code == EQ_EXPR ? GT_EXPR : LE_EXPR);
+      gimple_cond_set_code (cond, cmpcode);
     }
   else
     {
       gimple_assign_set_rhs1 (stmt, gimple_assign_lhs (g));
       gimple_assign_set_rhs2 (stmt, argm1);
-      gimple_assign_set_rhs_code (stmt, code == EQ_EXPR ? GT_EXPR : LE_EXPR);
+      gimple_assign_set_rhs_code (stmt, cmpcode);
     }
   update_stmt (stmt);
   gimple_stmt_iterator gsi2 = gsi_for_stmt (call);