FreeChainXenon/gcc
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

tree-ssa-math-opts: popcount (X) == 1 to (X ^ (X - 1)) > (X - 1) optimization [PR90693]

Browse source 
Per the earlier discussions on this PR, the following patch folds
popcount (x) == 1 (and != 1) into (x ^ (x - 1)) > x - 1 (or <=)
if the corresponding popcount optab isn't implemented (I think any
double-word popcount or call will be necessarily slower than the
above cheap 3 op check and even for -Os larger or same size).

I've noticed e.g. C++ aligned new starts with std::has_single_bit
which does popcount (x) == 1.

As a follow-up, I'm considering changing in this routine the popcount
call to IFN_POPCOUNT with 2 arguments and during expansion test costs.

2023-11-20  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/90693
	* tree-ssa-math-opts.cc (match_single_bit_test): New function.
	(math_opts_dom_walker::after_dom_children): Call it for EQ_EXPR
	and NE_EXPR assignments and GIMPLE_CONDs.

	* gcc.target/i386/pr90693.c: New test.
This commit is contained in:
Jakub Jelinek 2023-11-20 10:00:09 +01:00
parent 99fad213d5
commit d0b6b7f8a6
2 changed files with 104 additions and 1 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

29
gcc/testsuite/gcc.target/i386/pr90693.c Normal file
View file

@ -0,0 +1,29 @@
/* 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)
{
return __builtin_popcount (x) == 1;
}
int
bar (unsigned int x)
{
return (x ^ (x - 1)) > x - 1;
}
int
baz (unsigned long long x)
{
return __builtin_popcountll (x) == 1;
}
int
qux (unsigned long long x)
{
return (x ^ (x - 1)) > x - 1;
}

76
gcc/tree-ssa-math-opts.cc
View file

@ -5154,6 +5154,72 @@ match_uaddc_usubc (gimple_stmt_iterator *gsi, gimple *stmt, tree_code code)
return true;
}
/* Replace .POPCOUNT (x) == 1 or .POPCOUNT (x) != 1 with
(x & (x - 1)) > x - 1 or (x & (x - 1)) <= x - 1 if .POPCOUNT
isn't a direct optab. */
static void
match_single_bit_test (gimple_stmt_iterator *gsi, gimple *stmt)
{
tree clhs, crhs;
enum tree_code code;
if (gimple_code (stmt) == GIMPLE_COND)
{
clhs = gimple_cond_lhs (stmt);
crhs = gimple_cond_rhs (stmt);
code = gimple_cond_code (stmt);
}
else
{
clhs = gimple_assign_rhs1 (stmt);
crhs = gimple_assign_rhs2 (stmt);
code = gimple_assign_rhs_code (stmt);
}
if (code != EQ_EXPR && code != NE_EXPR)
return;
if (TREE_CODE (clhs) != SSA_NAME || !integer_onep (crhs))
return;
gimple *call = SSA_NAME_DEF_STMT (clhs);
combined_fn cfn = gimple_call_combined_fn (call);
switch (cfn)
{
CASE_CFN_POPCOUNT:
break;
default:
return;
}
if (!has_single_use (clhs))
return;
tree arg = gimple_call_arg (call, 0);
tree type = TREE_TYPE (arg);
if (!INTEGRAL_TYPE_P (type))
return;
if (direct_internal_fn_supported_p (IFN_POPCOUNT, type, OPTIMIZE_FOR_BOTH))
return;
tree argm1 = make_ssa_name (type);
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);
gsi_insert_before (gsi, g, GSI_SAME_STMT);
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);
}
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);
}
update_stmt (stmt);
gimple_stmt_iterator gsi2 = gsi_for_stmt (call);
gsi_remove (&gsi2, true);
release_defs (call);
}
/* Return true if target has support for divmod. */
static bool
@ -5807,6 +5873,11 @@ math_opts_dom_walker::after_dom_children (basic_block bb)
match_uaddc_usubc (&gsi, stmt, code);
break;
case EQ_EXPR:
case NE_EXPR:
match_single_bit_test (&gsi, stmt);
break;
default:;
}
}
@ -5872,7 +5943,10 @@ math_opts_dom_walker::after_dom_children (basic_block bb)
}
}
else if (gimple_code (stmt) == GIMPLE_COND)
optimize_spaceship (as_a <gcond *> (stmt));
{
match_single_bit_test (&gsi, stmt);
optimize_spaceship (as_a <gcond *> (stmt));
}
gsi_next (&gsi);
}
if (fma_state.m_deferring_p