https://gcc.gnu.org/g:481f96296e87b42b7f25944edd627cc9211dd803
commit r16-3300-g481f96296e87b42b7f25944edd627cc9211dd803
Author: Richard Sandiford <richard.sandif...@arm.com>
Date: Wed Aug 20 13:20:02 2025 +0100
rtl-ssa: Fix thinko when adding live-out uses
While testing a later patch, I found that create_degenerate_phi
had an inverted test for bitmap_set_bit. It was assuming that
the return value was the previous bit value, rather than a
"something changed" value. :(
Also, the call to add_live_out_use shouldn't be conditional
on the DF_LR_OUT operation, since the register could be live-out
because of uses later in the same EBB (which do not require a
live-out use to be added to the rtl-ssa instruction). Instead,
add_live_out should itself check whether a live-out use already exists.
gcc/
* rtl-ssa/blocks.cc (function_info::create_degenerate_phi): Fix
inverted test of bitmap_set_bit. Call add_live_out_use even
if the register was previously live-out from the predecessor block.
Instead...
(function_info::add_live_out_use): ...check here whether a live-out
use already exists.
Diff:
---
gcc/rtl-ssa/blocks.cc | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)
diff --git a/gcc/rtl-ssa/blocks.cc b/gcc/rtl-ssa/blocks.cc
index 953fd9e516ed..a57b9e15f13c 100644
--- a/gcc/rtl-ssa/blocks.cc
+++ b/gcc/rtl-ssa/blocks.cc
@@ -315,15 +315,14 @@ function_info::add_live_out_use (bb_info *bb, set_info
*def)
// If the end of the block already has an artificial use, that use
// acts to make DEF live at the appropriate point.
- use_info *use = def->last_nondebug_insn_use ();
- if (use && use->insn () == bb->end_insn ())
+ if (find_use (def, bb->end_insn ()).matching_use ())
return;
// Currently there is no need to maintain a backward link from the end
// instruction to the list of live-out uses. Such a list would be
// expensive to update if it was represented using the usual insn_info
// access arrays.
- use = allocate<use_info> (bb->end_insn (), def->resource (), def);
+ auto *use = allocate<use_info> (bb->end_insn (), def->resource (), def);
use->set_is_live_out_use (true);
add_use (use);
}
@@ -540,12 +539,12 @@ function_info::create_degenerate_phi (ebb_info *ebb,
set_info *def)
basic_block pred_cfg_bb = single_pred (ebb->first_bb ()->cfg_bb ());
bb_info *pred_bb = this->bb (pred_cfg_bb);
- if (!bitmap_set_bit (DF_LR_IN (ebb->first_bb ()->cfg_bb ()), regno))
+ if (bitmap_set_bit (DF_LR_IN (ebb->first_bb ()->cfg_bb ()), regno))
{
// The register was not previously live on entry to EBB and
// might not have been live on exit from PRED_BB either.
- if (bitmap_set_bit (DF_LR_OUT (pred_cfg_bb), regno))
- add_live_out_use (pred_bb, def);
+ bitmap_set_bit (DF_LR_OUT (pred_cfg_bb), regno);
+ add_live_out_use (pred_bb, def);
}
else
{
