Hi!
In the following testcase we have a -fcompare-debug failure, because
can_move_invariant_reg doesn't ignore DEBUG_INSNs in its decisions.
In the testcase we have due to uninitialized variable:
loop_header
debug_insn using pseudo84
pseudo84 = invariant
insn using pseudo84
end loop
and with -g decide not to move the pseudo84 = invariant before the
loop header; in this case not resetting the debug insns might be fine.
But, we could have also:
pseudo84 = whatever
loop_header
debug_insn using pseudo84
pseudo84 = invariant
insn using pseudo84
end loop
and in that case not resetting the debug insns would result in wrong-debug.
And, we don't really have generally a good substitution on what pseudo84
contains, it could inherit various values from different paths.
So, the following patch ignores DEBUG_INSNs in the decisions, and if there
are any that previously prevented the optimization, resets them before
return true.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2021-12-28 Jakub Jelinek <ja...@redhat.com>
PR rtl-optimization/103837
* loop-invariant.c (can_move_invariant_reg): Ignore DEBUG_INSNs in
the decisions whether to return false or continue and right before
returning true reset those debug insns that previously caused
returning false.
* gcc.dg/pr103837.c: New test.
--- gcc/loop-invariant.c.jj 2021-11-25 08:33:08.619232065 +0100
+++ gcc/loop-invariant.c 2021-12-27 13:44:44.094132316 +0100
@@ -1691,6 +1691,7 @@ can_move_invariant_reg (class loop *loop
unsigned int dest_regno, defs_in_loop_count = 0;
rtx_insn *insn = inv->insn;
basic_block bb = BLOCK_FOR_INSN (inv->insn);
+ auto_vec <rtx_insn *, 16> debug_insns_to_reset;
/* We ignore hard register and memory access for cost and complexity reasons.
Hard register are few at this stage and expensive to consider as they
@@ -1725,10 +1726,13 @@ can_move_invariant_reg (class loop *loop
continue;
/* Don't move if a use is not dominated by def in insn. */
- if (use_bb == bb && DF_INSN_LUID (insn) >= DF_INSN_LUID (use_insn))
- return false;
- if (!dominated_by_p (CDI_DOMINATORS, use_bb, bb))
- return false;
+ if ((use_bb == bb && DF_INSN_LUID (insn) >= DF_INSN_LUID (use_insn))
+ || !dominated_by_p (CDI_DOMINATORS, use_bb, bb))
+ {
+ if (!DEBUG_INSN_P (use_insn))
+ return false;
+ debug_insns_to_reset.safe_push (use_insn);
+ }
}
/* Check for other defs. Any other def in the loop might reach a use
@@ -1751,6 +1755,13 @@ can_move_invariant_reg (class loop *loop
return false;
}
+ /* Reset debug uses if a use is not dominated by def in insn. */
+ for (auto use_insn : debug_insns_to_reset)
+ {
+ INSN_VAR_LOCATION_LOC (use_insn) = gen_rtx_UNKNOWN_VAR_LOC ();
+ df_insn_rescan (use_insn);
+ }
+
return true;
}
--- gcc/testsuite/gcc.dg/pr103837.c.jj 2021-12-27 13:42:23.262111770 +0100
+++ gcc/testsuite/gcc.dg/pr103837.c 2021-12-27 13:41:36.635767125 +0100
@@ -0,0 +1,19 @@
+/* PR rtl-optimization/103837 */
+/* { dg-do compile } */
+/* { dg-options "-Og -fcompare-debug -fmove-loop-invariants
-fnon-call-exceptions -fexceptions -fdelete-dead-exceptions -fno-tree-dce -w" }
*/
+
+unsigned long int
+foo (int x)
+{
+ double a;
+ int b;
+ unsigned long int ret = a;
+
+ for (;;)
+ {
+ b = !!((int) a);
+ a = x;
+ }
+
+ return ret;
+}
Jakub
