| Message ID | ormtfniktt.fsf@lxoliva.fsfla.org |
|---|---|
| State | New |
| Headers | show |
| Series | [PR105455] Set edge probabilities when hardening conditionals | expand |
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>
On May 12, 2022, Richard Biener <richard.guenther@gmail.com> wrote: >> Regstrapped on x86_64-linux-gnu. Ok to install? > OK. Thanks. I failed to ask, but I'm confident this is also ok for gcc-12, so I'm putting it in there as well. Please let me know otherwise. >> PR rtl-optimization/105455 >> * gimple-harden-conditionals.cc (insert_check_and_trap): Set >> probabilities for newly-conditional edges.
On Fri, May 13, 2022 at 8:03 AM Alexandre Oliva <oliva@adacore.com> wrote: > > On May 12, 2022, Richard Biener <richard.guenther@gmail.com> wrote: > > >> Regstrapped on x86_64-linux-gnu. Ok to install? > > > OK. > > Thanks. I failed to ask, but I'm confident this is also ok for gcc-12, > so I'm putting it in there as well. Please let me know otherwise. Yes, sure. > >> PR rtl-optimization/105455 > >> * gimple-harden-conditionals.cc (insert_check_and_trap): Set > >> probabilities for newly-conditional edges. > > -- > 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>
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 (); + } +}