On Wed, 21 Oct 2020, Jakub Jelinek wrote:
> Hi!
>
> While we have at the RTL level noce_try_ifelse_collapse combined with
> simplify_cond_clz_ctz, that optimization doesn't always trigger because
> e.g. on powerpc there is an define_insn to compare a reg against zero and
> copy that register to another one and so we end up with a different pseudo
> in the simplify_cond_clz_ctz test and punt.
>
> For targets that define C?Z_DEFINED_VALUE_AT_ZERO to 2 for certain modes,
> we can optimize it already in phiopt though, just need to ensure that
> we transform the __builtin_c?z* calls into .C?Z ifns because my recent
> VRP changes codified that the builtin calls are always undefined at zero,
> while ifns honor C?Z_DEFINED_VALUE_AT_ZERO equal to 2.
> And, in phiopt we already have popcount handling that does pretty much the
> same thing, except for always using a zero value rather than the one set
> by C?Z_DEFINED_VALUE_AT_ZERO.
>
> So, this patch extends that function to handle not just popcount, but also
> clz and ctz.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> 2020-10-20 Jakub Jelinek <ja...@redhat.com>
>
> PR tree-optimization/97503
> * tree-ssa-phiopt.c (cond_removal_in_popcount_pattern): Rename to ...
> (cond_removal_in_popcount_clz_ctz_pattern): ... this. Handle not just
> popcount, but also clz and ctz if it has C?Z_DEFINED_VALUE_AT_ZERO 2.
>
> * gcc.dg/tree-ssa/pr97503.c: New test.
>
> --- gcc/tree-ssa-phiopt.c.jj 2020-07-28 15:39:10.075755306 +0200
> +++ gcc/tree-ssa-phiopt.c 2020-10-20 17:46:16.971329154 +0200
> @@ -61,8 +61,9 @@ static bool minmax_replacement (basic_bl
> edge, edge, gimple *, tree, tree);
> static bool abs_replacement (basic_block, basic_block,
> edge, edge, gimple *, tree, tree);
> -static bool cond_removal_in_popcount_pattern (basic_block, basic_block,
> - edge, edge, gimple *, tree, tree);
> +static bool cond_removal_in_popcount_clz_ctz_pattern (basic_block,
> basic_block,
> + edge, edge, gimple *,
> + tree, tree);
> static bool cond_store_replacement (basic_block, basic_block, edge, edge,
> hash_set<tree> *);
> static bool cond_if_else_store_replacement (basic_block, basic_block,
> basic_block);
> @@ -344,8 +345,9 @@ tree_ssa_phiopt_worker (bool do_store_el
> else if (abs_replacement (bb, bb1, e1, e2, phi, arg0, arg1))
> cfgchanged = true;
> else if (!early_p
> - && cond_removal_in_popcount_pattern (bb, bb1, e1, e2,
> - phi, arg0, arg1))
> + && cond_removal_in_popcount_clz_ctz_pattern (bb, bb1, e1,
> + e2, phi, arg0,
> + arg1))
> cfgchanged = true;
> else if (minmax_replacement (bb, bb1, e1, e2, phi, arg0, arg1))
> cfgchanged = true;
> @@ -1777,16 +1779,20 @@ minmax_replacement (basic_block cond_bb,
>
> <bb 4>
> c_12 = PHI <_9(2)>
> -*/
> +
> + Similarly for __builtin_clz or __builtin_ctz if
> + C?Z_DEFINED_VALUE_AT_ZERO is 2, optab is present and
> + instead of 0 above it uses the value from that macro. */
>
> static bool
> -cond_removal_in_popcount_pattern (basic_block cond_bb, basic_block middle_bb,
> - edge e1, edge e2,
> - gimple *phi, tree arg0, tree arg1)
> +cond_removal_in_popcount_clz_ctz_pattern (basic_block cond_bb,
> + basic_block middle_bb,
> + edge e1, edge e2, gimple *phi,
> + tree arg0, tree arg1)
> {
> gimple *cond;
> gimple_stmt_iterator gsi, gsi_from;
> - gimple *popcount;
> + gimple *call;
> gimple *cast = NULL;
> tree lhs, arg;
>
> @@ -1804,35 +1810,65 @@ cond_removal_in_popcount_pattern (basic_
> gsi_next_nondebug (&gsi);
> if (!gsi_end_p (gsi))
> {
> - popcount = gsi_stmt (gsi);
> + call = gsi_stmt (gsi);
> gsi_next_nondebug (&gsi);
> if (!gsi_end_p (gsi))
> return false;
> }
> else
> {
> - popcount = cast;
> + call = cast;
> cast = NULL;
> }
>
> - /* Check that we have a popcount builtin. */
> - if (!is_gimple_call (popcount))
> + /* Check that we have a popcount/clz/ctz builtin. */
> + if (!is_gimple_call (call) || gimple_call_num_args (call) != 1)
> return false;
> - combined_fn cfn = gimple_call_combined_fn (popcount);
> +
> + arg = gimple_call_arg (call, 0);
> + lhs = gimple_get_lhs (call);
> +
> + if (lhs == NULL_TREE)
> + return false;
> +
> + combined_fn cfn = gimple_call_combined_fn (call);
> + internal_fn ifn = IFN_LAST;
> + int val = 0;
> switch (cfn)
> {
> CASE_CFN_POPCOUNT:
> break;
> + CASE_CFN_CLZ:
> + if (INTEGRAL_TYPE_P (TREE_TYPE (arg)))
> + {
> + scalar_int_mode mode = SCALAR_INT_TYPE_MODE (TREE_TYPE (arg));
> + if (optab_handler (clz_optab, mode) != CODE_FOR_nothing
I think it's better to use
direct_internal_fn_supported_p (IFN_CLZ, TREE_TYPE (arg),
OPTIMIZE_FOR_BOTH);
for these checks nowadays. Otherwise OK.
Thanks,
Richard.
> + && CLZ_DEFINED_VALUE_AT_ZERO (mode, val) == 2)
> + {
> + ifn = IFN_CLZ;
> + break;
> + }
> + }
> + return false;
> + CASE_CFN_CTZ:
> + if (INTEGRAL_TYPE_P (TREE_TYPE (arg)))
> + {
> + scalar_int_mode mode = SCALAR_INT_TYPE_MODE (TREE_TYPE (arg));
> + if (optab_handler (ctz_optab, mode) != CODE_FOR_nothing
> + && CTZ_DEFINED_VALUE_AT_ZERO (mode, val) == 2)
> + {
> + ifn = IFN_CTZ;
> + break;
> + }
> + }
> + return false;
> default:
> return false;
> }
>
> - arg = gimple_call_arg (popcount, 0);
> - lhs = gimple_get_lhs (popcount);
> -
> if (cast)
> {
> - /* We have a cast stmt feeding popcount builtin. */
> + /* We have a cast stmt feeding popcount/clz/ctz builtin. */
> /* Check that we have a cast prior to that. */
> if (gimple_code (cast) != GIMPLE_ASSIGN
> || !CONVERT_EXPR_CODE_P (gimple_assign_rhs_code (cast)))
> @@ -1845,7 +1881,7 @@ cond_removal_in_popcount_pattern (basic_
>
> cond = last_stmt (cond_bb);
>
> - /* Cond_bb has a check for b_4 [!=|==] 0 before calling the popcount
> + /* Cond_bb has a check for b_4 [!=|==] 0 before calling the
> popcount/clz/ctz
> builtin. */
> if (gimple_code (cond) != GIMPLE_COND
> || (gimple_cond_code (cond) != NE_EXPR
> @@ -1865,10 +1901,13 @@ cond_removal_in_popcount_pattern (basic_
> }
>
> /* Check PHI arguments. */
> - if (lhs != arg0 || !integer_zerop (arg1))
> + if (lhs != arg0
> + || TREE_CODE (arg1) != INTEGER_CST
> + || wi::to_wide (arg1) != val)
> return false;
>
> - /* And insert the popcount builtin and cast stmt before the cond_bb. */
> + /* And insert the popcount/clz/ctz builtin and cast stmt before the
> + cond_bb. */
> gsi = gsi_last_bb (cond_bb);
> if (cast)
> {
> @@ -1876,9 +1915,19 @@ cond_removal_in_popcount_pattern (basic_
> gsi_move_before (&gsi_from, &gsi);
> reset_flow_sensitive_info (gimple_get_lhs (cast));
> }
> - gsi_from = gsi_for_stmt (popcount);
> - gsi_move_before (&gsi_from, &gsi);
> - reset_flow_sensitive_info (gimple_get_lhs (popcount));
> + gsi_from = gsi_for_stmt (call);
> + if (ifn == IFN_LAST || gimple_call_internal_p (call))
> + gsi_move_before (&gsi_from, &gsi);
> + else
> + {
> + /* For __builtin_c[lt]z* force .C[LT]Z ifn, because only
> + the latter is well defined at zero. */
> + call = gimple_build_call_internal (ifn, 1, gimple_call_arg (call, 0));
> + gimple_call_set_lhs (call, lhs);
> + gsi_insert_before (&gsi, call, GSI_SAME_STMT);
> + gsi_remove (&gsi_from, true);
> + }
> + reset_flow_sensitive_info (lhs);
>
> /* Now update the PHI and remove unneeded bbs. */
> replace_phi_edge_with_variable (cond_bb, e2, phi, lhs);
> --- gcc/testsuite/gcc.dg/tree-ssa/pr97503.c.jj 2020-10-20
> 18:14:46.862749687 +0200
> +++ gcc/testsuite/gcc.dg/tree-ssa/pr97503.c 2020-10-20 18:17:13.618640295
> +0200
> @@ -0,0 +1,19 @@
> +/* PR tree-optimization/97503 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-optimized" } */
> +/* { dg-additional-options "-mbmi -mlzcnt" { target i?86-*-* x86_64-*-* } }
> */
> +/* { dg-final { scan-tree-dump-times "\.CLZ" 2 "optimized" { target { {
> i?86-*-* x86_64-*-* aarch64-*-* powerpc*-*-* } && lp64 } } } } */
> +/* { dg-final { scan-tree-dump-not "__builtin_clz" "optimized" { target { {
> i?86-*-* x86_64-*-* aarch64-*-* powerpc*-*-*} && lp64 } } } } */
> +/* { dg-final { scan-tree-dump-not "PHI <" "optimized" { target { { i?86-*-*
> x86_64-*-* aarch64-*-* powerpc*-*-*} && lp64 } } } } */
> +
> +int
> +foo (int x)
> +{
> + return x ? __builtin_clz (x) : 32;
> +}
> +
> +int
> +bar (unsigned long long x)
> +{
> + return x ? __builtin_clzll (x) : 64;
> +}
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imend
