[gcc r13-380] [PR105455] Set edge probabilities when hardening conditionals

[gcc r13-380] [PR105455] Set edge probabilities when hardening conditionals

[Alexandre Oliva]

https://gcc.gnu.org/g:90a8eab4a1292430467f68b65e5127f7760acc94

commit r13-380-g90a8eab4a1292430467f68b65e5127f7760acc94
Author: Alexandre Oliva <oliva@adacore.com>
Date:   Wed May 11 04:27:42 2022 -0300

    [PR105455] Set edge probabilities when hardening conditionals
    
    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.
    
    
    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.

Diff:
---
 gcc/gimple-harden-conditionals.cc |  2 ++
 gcc/testsuite/gcc.dg/pr105455.c   | 17 +++++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/gcc/gimple-harden-conditionals.cc b/gcc/gimple-harden-conditionals.cc
index c7e5e077a74..19ceb8a4bd6 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 00000000000..81e9154baa1
--- /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 ();
+    }
+}