On Thu, May 12, 2022 at 3:48 AM Alexandre Oliva via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
>
> When turning unconditional edges into conditional, as in
> gimple-harden-conditionals.cc:insert_check_and_trap, the newly-created
> edge's probability comes out uninitialized, while the previously
> unconditional edge's probability is presumably
> profile_probability::always.
>
> Mixing initialized and uninitialized probabilities before expand
> breaks predict.cc:force_edge_cold: the initialized probability may end
> up copied to a REG_BR_PROB note in a conditional branch insn, but if
> force_edge_cold is called on that edge, it will find another edge with
> uninitialized probability and assume the note is absent. Later on,
> rtl_verify_edges complains that the note does not match the
> probability modified by force_edge_cold in the edge.
>
> This patch sets probabilities for edges affected by hardening of
> conditionals, both the newly-created edges to trap blocks and the
> previously-unconditional edges, so that the former are considered
> never taken, while the latter are confirmed as always taken.
>
> Regstrapped on x86_64-linux-gnu. Ok to install?
OK.
>
> for gcc/ChangeLog
>
> PR rtl-optimization/105455
> * gimple-harden-conditionals.cc (insert_check_and_trap): Set
> probabilities for newly-conditional edges.
>
> for gcc/testsuite/ChangeLog
>
> PR rtl-optimization/105455
> * gcc.dg/pr105455.c: New.
> ---
> gcc/gimple-harden-conditionals.cc | 2 ++
> gcc/testsuite/gcc.dg/pr105455.c | 17 +++++++++++++++++
> 2 files changed, 19 insertions(+)
> create mode 100644 gcc/testsuite/gcc.dg/pr105455.c
>
> diff --git a/gcc/gimple-harden-conditionals.cc
> b/gcc/gimple-harden-conditionals.cc
> index 28c4810f0a78e..240d0e5acd87a 100644
> --- a/gcc/gimple-harden-conditionals.cc
> +++ b/gcc/gimple-harden-conditionals.cc
> @@ -254,8 +254,10 @@ insert_check_and_trap (location_t loc,
> gimple_stmt_iterator *gsip,
> equality. */
> single_succ_edge (chk)->flags &= ~EDGE_FALLTHRU;
> single_succ_edge (chk)->flags |= neg_true_false_flag;
> + single_succ_edge (chk)->probability = profile_probability::always ();
> edge e = make_edge (chk, trp, true_false_flag);
> e->goto_locus = loc;
> + e->probability = profile_probability::never ();
>
> if (dom_info_available_p (CDI_DOMINATORS))
> set_immediate_dominator (CDI_DOMINATORS, trp, chk);
> diff --git a/gcc/testsuite/gcc.dg/pr105455.c b/gcc/testsuite/gcc.dg/pr105455.c
> new file mode 100644
> index 0000000000000..81e9154baa1c3
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/pr105455.c
> @@ -0,0 +1,17 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O1 -fharden-conditional-branches -funroll-loops --param
> max-loop-header-insns=1" } */
> +
> +__attribute__ ((cold)) void
> +bar (void);
> +
> +void
> +foo (int x)
> +{
> + if (x)
> + {
> + int i;
> +
> + for (i = 0; i < 101; ++i)
> + bar ();
> + }
> +}
>
>
> --
> Alexandre Oliva, happy hacker https://FSFLA.org/blogs/lxo/
> Free Software Activist GNU Toolchain Engineer
> Disinformation flourishes because many people care deeply about injustice
> but very few check the facts. Ask me about <https://stallmansupport.org>
