On Tue, 1 Feb 2022, Jakub Jelinek wrote:
> Hi!
>
> The following testcase fails -fcompare-debug, because expand_vector_comparison
> since r11-1786-g1ac9258cca8030745d3c0b8f63186f0adf0ebc27 sets
> vec_cond_expr_only when it sees some use other than VEC_COND_EXPR that uses
> the lhs in its condition.
> Obviously we should ignore debug stmts when doing so, e.g. by not pushing
> them to uses.
> That would be a 2 liner change, but while looking at it, I'm also worried
> about VEC_COND_EXPRs that would use the lhs in more than one operand,
> like VEC_COND_EXPR <lhs, lhs, something> or VEC_COND_EXPR <lhs, something,
> lhs>
> (sure, they ought to be folded, but what if they weren't). Because if
> something like that happens, then FOR_EACH_IMM_USE_FAST would push the same
> stmt multiple times and expand_vector_condition can return true even when
> it modifies it (for vector bool masking).
> And lastly, it seems quite wasteful to safe_push statements that will just
> cause vec_cond_expr_only = false; and break; in the second loop, both for
> cases like 1000 immediate non-VEC_COND_EXPR uses and for cases like
> 999 VEC_COND_EXPRs with lhs in cond followed by a single non-VEC_COND_EXPR
> use. So this patch only pushes VEC_COND_EXPRs there. As
> expand_vector_condition modifies the IL, it checks the condition again as
> before.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
So I think it's all fine besides the handling of VEC_COND_EXPRs where
the use is in rhs1 and rhs2 and/or rhs3 - I don't really understand
your worry here but shouldn't the stmt end up on the vector at least
once? You can use gimple_assign_rhs1_ptr to see whether the
use is the rhs1 use comparing that with USE_PTR IIRC. Btw, if you
never push VEC_COND_EXPRs with such double-use it's not necessary
to check again in the second loop?
That said, the other changes look reasonable.
Thanks,
Richard.
> 2022-02-01 Jakub Jelinek <ja...@redhat.com>
>
> PR middle-end/104307
> * tree-vect-generic.cc (expand_vector_comparison): Don't push debug
> stmts to uses vector, just set vec_cond_expr_only to false for
> non-VEC_COND_EXPRs instead of pushing them into uses. Treat
> VEC_COND_EXPRs that use lhs not just in rhs1, but rhs2 or rhs3 too
> like non-VEC_COND_EXPRs.
>
> * gcc.target/i386/pr104307.c: New test.
>
> --- gcc/tree-vect-generic.cc.jj 2022-01-20 11:30:45.641577244 +0100
> +++ gcc/tree-vect-generic.cc 2022-01-31 18:01:29.062568721 +0100
> @@ -436,29 +436,43 @@ expand_vector_comparison (gimple_stmt_it
> feeding a VEC_COND_EXPR statement. */
> auto_vec<gimple *> uses;
> FOR_EACH_IMM_USE_FAST (use_p, iterator, lhs)
> - uses.safe_push (USE_STMT (use_p));
> -
> - for (unsigned i = 0; i < uses.length (); i ++)
> {
> - gassign *use = dyn_cast<gassign *> (uses[i]);
> - if (use != NULL
> + gimple *use = USE_STMT (use_p);
> + if (is_gimple_debug (use))
> + continue;
> + if (is_gimple_assign (use)
> && gimple_assign_rhs_code (use) == VEC_COND_EXPR
> - && gimple_assign_rhs1 (use) == lhs)
> - {
> - gimple_stmt_iterator it = gsi_for_stmt (use);
> - if (!expand_vector_condition (&it, dce_ssa_names))
> - {
> - vec_cond_expr_only = false;
> - break;
> - }
> - }
> + && gimple_assign_rhs1 (use) == lhs
> + && gimple_assign_rhs2 (use) != lhs
> + && gimple_assign_rhs3 (use) != lhs)
> + uses.safe_push (use);
> else
> - {
> - vec_cond_expr_only = false;
> - break;
> - }
> + vec_cond_expr_only = false;
> }
>
> + if (vec_cond_expr_only)
> + for (gimple *use : uses)
> + {
> + if (is_gimple_assign (use)
> + && gimple_assign_rhs_code (use) == VEC_COND_EXPR
> + && gimple_assign_rhs1 (use) == lhs
> + && gimple_assign_rhs2 (use) != lhs
> + && gimple_assign_rhs3 (use) != lhs)
> + {
> + gimple_stmt_iterator it = gsi_for_stmt (use);
> + if (!expand_vector_condition (&it, dce_ssa_names))
> + {
> + vec_cond_expr_only = false;
> + break;
> + }
> + }
> + else
> + {
> + vec_cond_expr_only = false;
> + break;
> + }
> + }
> +
> if (!uses.is_empty () && vec_cond_expr_only)
> return NULL_TREE;
>
> --- gcc/testsuite/gcc.target/i386/pr104307.c.jj 2022-01-31
> 17:34:42.163145798 +0100
> +++ gcc/testsuite/gcc.target/i386/pr104307.c 2022-01-31 17:35:14.111696698
> +0100
> @@ -0,0 +1,6 @@
> +/* PR middle-end/104307 */
> +/* { dg-do compile } */
> +/* { dg-require-effective-target int128 } */
> +/* { dg-options "-O2 -mavx512f -fcompare-debug " } */
> +
> +#include "pr78669.c"
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Ivo Totev; HRB 36809 (AG Nuernberg)
