On Tue, 5 Jan 2021, Jakub Jelinek wrote:
> Hi!
>
> As requested in the PR, the one's complement abs can be done more
> efficiently without cmov or branching.
>
> Had to change the ifcvt-onecmpl-abs-1.c testcase, we no longer optimize
> it in ifcvt, on x86_64 with -m32 we generate in the end the exact same
> code, but with -m64:
> movl %edi, %eax
> - notl %eax
> - cmpl %edi, %eax
> - cmovl %edi, %eax
> + sarl $31, %eax
> + xorl %edi, %eax
> ret
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
OK.
Thanks,
Richard.
> 2021-01-05 Jakub Jelinek <ja...@redhat.com>
>
> PR tree-optimization/96928
> * tree-ssa-phiopt.c (xor_replacement): New function.
> (tree_ssa_phiopt_worker): Call it.
>
> * gcc.dg/tree-ssa/pr96928.c: New test.
> * gcc.target/i386/ifcvt-onecmpl-abs-1.c: Remove -fdump-rtl-ce1,
> instead of scanning rtl dump for ifcvt message check assembly
> for xor instruction.
>
> --- gcc/tree-ssa-phiopt.c.jj 2021-01-04 10:25:38.638236032 +0100
> +++ gcc/tree-ssa-phiopt.c 2021-01-04 15:29:30.050005505 +0100
> @@ -62,6 +62,8 @@ 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 xor_replacement (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);
> @@ -346,6 +348,9 @@ 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
> + && xor_replacement (bb, bb1, e1, e2, phi, arg0, arg1))
> + cfgchanged = true;
> + else if (!early_p
> && cond_removal_in_popcount_clz_ctz_pattern (bb, bb1, e1,
> e2, phi, arg0,
> arg1))
> @@ -2097,6 +2102,109 @@ abs_replacement (basic_block cond_bb, ba
> /* Note that we optimized this PHI. */
> return true;
> }
> +
> +/* Optimize x < 0 ? ~y : y into (x >> (prec-1)) ^ y. */
> +
> +static bool
> +xor_replacement (basic_block cond_bb, basic_block middle_bb,
> + edge e0 ATTRIBUTE_UNUSED, edge e1,
> + gimple *phi, tree arg0, tree arg1)
> +{
> + if (!INTEGRAL_TYPE_P (TREE_TYPE (arg1)))
> + return false;
> +
> + /* OTHER_BLOCK must have only one executable statement which must have the
> + form arg0 = ~arg1 or arg1 = ~arg0. */
> +
> + gimple *assign = last_and_only_stmt (middle_bb);
> + /* If we did not find the proper one's complement assignment, then we
> cannot
> + optimize. */
> + if (assign == NULL)
> + return false;
> +
> + /* If we got here, then we have found the only executable statement
> + in OTHER_BLOCK. If it is anything other than arg = ~arg1 or
> + arg1 = ~arg0, then we cannot optimize. */
> + if (!is_gimple_assign (assign))
> + return false;
> +
> + if (gimple_assign_rhs_code (assign) != BIT_NOT_EXPR)
> + return false;
> +
> + tree lhs = gimple_assign_lhs (assign);
> + tree rhs = gimple_assign_rhs1 (assign);
> +
> + /* The assignment has to be arg0 = -arg1 or arg1 = -arg0. */
> + if (!(lhs == arg0 && rhs == arg1) && !(lhs == arg1 && rhs == arg0))
> + return false;
> +
> + gimple *cond = last_stmt (cond_bb);
> + tree result = PHI_RESULT (phi);
> +
> + /* Only relationals comparing arg[01] against zero are interesting. */
> + enum tree_code cond_code = gimple_cond_code (cond);
> + if (cond_code != LT_EXPR && cond_code != GE_EXPR)
> + return false;
> +
> + /* Make sure the conditional is x OP 0. */
> + tree clhs = gimple_cond_lhs (cond);
> + if (TREE_CODE (clhs) != SSA_NAME
> + || !INTEGRAL_TYPE_P (TREE_TYPE (clhs))
> + || TYPE_UNSIGNED (TREE_TYPE (clhs))
> + || TYPE_PRECISION (TREE_TYPE (clhs)) != TYPE_PRECISION (TREE_TYPE
> (arg1))
> + || !integer_zerop (gimple_cond_rhs (cond)))
> + return false;
> +
> + /* We need to know which is the true edge and which is the false
> + edge so that we know if have xor or inverted xor. */
> + edge true_edge, false_edge;
> + extract_true_false_edges_from_block (cond_bb, &true_edge, &false_edge);
> +
> + /* For GE_EXPR, if the true edge goes to OTHER_BLOCK, then we
> + will need to invert the result. Similarly for LT_EXPR if
> + the false edge goes to OTHER_BLOCK. */
> + edge e;
> + if (cond_code == GE_EXPR)
> + e = true_edge;
> + else
> + e = false_edge;
> +
> + bool invert = e->dest == middle_bb;
> +
> + result = duplicate_ssa_name (result, NULL);
> +
> + gimple_stmt_iterator gsi = gsi_last_bb (cond_bb);
> +
> + int prec = TYPE_PRECISION (TREE_TYPE (clhs));
> + gimple *new_stmt
> + = gimple_build_assign (make_ssa_name (TREE_TYPE (clhs)), RSHIFT_EXPR,
> clhs,
> + build_int_cst (integer_type_node, prec - 1));
> + gsi_insert_before (&gsi, new_stmt, GSI_SAME_STMT);
> +
> + if (!useless_type_conversion_p (TREE_TYPE (result), TREE_TYPE (clhs)))
> + {
> + new_stmt = gimple_build_assign (make_ssa_name (TREE_TYPE (result)),
> + NOP_EXPR, gimple_assign_lhs (new_stmt));
> + gsi_insert_before (&gsi, new_stmt, GSI_SAME_STMT);
> + }
> + lhs = gimple_assign_lhs (new_stmt);
> +
> + if (invert)
> + {
> + new_stmt = gimple_build_assign (make_ssa_name (TREE_TYPE (result)),
> + BIT_NOT_EXPR, rhs);
> + gsi_insert_before (&gsi, new_stmt, GSI_SAME_STMT);
> + rhs = gimple_assign_lhs (new_stmt);
> + }
> +
> + new_stmt = gimple_build_assign (result, BIT_XOR_EXPR, lhs, rhs);
> + gsi_insert_before (&gsi, new_stmt, GSI_NEW_STMT);
> +
> + replace_phi_edge_with_variable (cond_bb, e1, phi, result);
> +
> + /* Note that we optimized this PHI. */
> + return true;
> +}
>
> /* Auxiliary functions to determine the set of memory accesses which
> can't trap because they are preceded by accesses to the same memory
> --- gcc/testsuite/gcc.dg/tree-ssa/pr96928.c.jj 2021-01-04
> 15:41:34.803857493 +0100
> +++ gcc/testsuite/gcc.dg/tree-ssa/pr96928.c 2021-01-04 15:43:16.794710865
> +0100
> @@ -0,0 +1,38 @@
> +/* PR tree-optimization/96928 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-phiopt2" } */
> +/* { dg-final { scan-tree-dump-times " = a_\[0-9]*\\\(D\\\) >> " 5 "phiopt2"
> } } */
> +/* { dg-final { scan-tree-dump-times " = ~c_\[0-9]*\\\(D\\\);" 1 "phiopt2" }
> } */
> +/* { dg-final { scan-tree-dump-times " = ~" 1 "phiopt2" } } */
> +/* { dg-final { scan-tree-dump-times " = \[abc_0-9\\\(\\\)D]* \\\^ " 5
> "phiopt2" } } */
> +/* { dg-final { scan-tree-dump-not "a < 0" "phiopt2" } } */
> +
> +int
> +foo (int a)
> +{
> + return a < 0 ? ~a : a;
> +}
> +
> +int
> +bar (int a, int b)
> +{
> + return a < 0 ? ~b : b;
> +}
> +
> +unsigned
> +baz (int a, unsigned int b)
> +{
> + return a < 0 ? ~b : b;
> +}
> +
> +unsigned
> +qux (int a, unsigned int c)
> +{
> + return a >= 0 ? ~c : c;
> +}
> +
> +int
> +corge (int a, int b)
> +{
> + return a >= 0 ? b : ~b;
> +}
> --- gcc/testsuite/gcc.target/i386/ifcvt-onecmpl-abs-1.c.jj 2020-01-12
> 11:54:37.946390280 +0100
> +++ gcc/testsuite/gcc.target/i386/ifcvt-onecmpl-abs-1.c 2021-01-05
> 09:39:14.326747916 +0100
> @@ -1,5 +1,5 @@
> /* { dg-do compile } */
> -/* { dg-options "-O2 -fdump-rtl-ce1" } */
> +/* { dg-options "-O2" } */
>
> /* Check code generation for one's complement version of abs */
>
> @@ -10,4 +10,4 @@ int onecmplabs(int x)
> return x;
> }
>
> -/* { dg-final { scan-rtl-dump "succeeded through noce_try_abs" "ce1" } } */
> +/* { dg-final { scan-assembler "\txor" } } */
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
