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[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.
This commit is contained in:
Alexandre Oliva 2022-05-11 04:27:42 -03:00 committed by Alexandre Oliva
parent 8ab4b48415
commit 90a8eab4a1
2 changed files with 19 additions and 0 deletions
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2
gcc/gimple-harden-conditionals.cc
View File

@ -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);

17
gcc/testsuite/gcc.dg/pr105455.c Normal file
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@ -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 ();
}
}