https://gcc.gnu.org/g:f9a6efa7a71e80a0989ac91fb7f282468471bb46
commit r16-1724-gf9a6efa7a71e80a0989ac91fb7f282468471bb46
Author: Alexandre Oliva <ol...@adacore.com>
Date: Thu Jun 26 21:01:29 2025 -0300
[lra] catch all to-sp eliminations with nonzero offsets [PR120424]
An x86_64-linux-gnu native with ix86_frame_pointer_required modified
to return true for nonzero frames, to exercize
lra_update_fp2sp_elimination, reveals in stage1 testing that wrong
code is generated for gcc.c-torture/execute/ieee/fp-cmp-8l.c:
argp-to-sp eliminations are used for one_test to pass its arguments on
to *pos, and the sp offsets survive the disabling of that elimination.
We didn't really have to disable that elimination, but the x86 backend
disables eliminations to sp if frame_pointer_needed.
This change extends the catching of fp2sp eliminations to all (?)
eliminations to sp with nonzero offsets, since none of them can be
properly reversed and would silently lead to wrong code.
By accepting nonzero offsets, we bootstrap with
-maccumulate-outgoing-args on x86_64-linux-gnu (with
ix86_frame_pointer_required modified to return true on nonzero frame
size).
for gcc/ChangeLog
PR rtl-optimization/120424
* lra-eliminations.cc (elimination_2sp_occurred_p): Rename
from...
(elimination_fp2sp_occured_p): ... this. Adjust all uses.
(lra_eliminate_regs_1): Don't require a from-frame-pointer
elimination to set it.
(update_reg_eliminate): Likewise to test it.
Diff:
---
gcc/lra-eliminations.cc | 46 +++++++++++++++++++++++++---------------------
1 file changed, 25 insertions(+), 21 deletions(-)
diff --git a/gcc/lra-eliminations.cc b/gcc/lra-eliminations.cc
index 9cdd0c5ff53a..045f2dcf23ef 100644
--- a/gcc/lra-eliminations.cc
+++ b/gcc/lra-eliminations.cc
@@ -309,8 +309,18 @@ move_plus_up (rtx x)
return x;
}
-/* Flag that we already did frame pointer to stack pointer elimination. */
-static bool elimination_fp2sp_occured_p = false;
+/* Flag that we already applied nonzero stack pointer elimination
+ offset; such sp updates cannot currently be undone. */
+static bool elimination_2sp_occurred_p = false;
+
+/* Take note of any nonzero sp-OFFSET used in eliminations to sp. */
+static inline poly_int64
+note_spoff (poly_int64 offset)
+{
+ if (maybe_ne (offset, 0))
+ elimination_2sp_occurred_p = true;
+ return offset;
+}
/* Scan X and replace any eliminable registers (such as fp) with a
replacement (such as sp) if SUBST_P, plus an offset. The offset is
@@ -369,13 +379,10 @@ lra_eliminate_regs_1 (rtx_insn *insn, rtx x, machine_mode
mem_mode,
{
rtx to = subst_p ? ep->to_rtx : ep->from_rtx;
- if (ep->to_rtx == stack_pointer_rtx && ep->from ==
FRAME_POINTER_REGNUM)
- elimination_fp2sp_occured_p = true;
-
if (maybe_ne (update_sp_offset, 0))
{
if (ep->to_rtx == stack_pointer_rtx)
- return plus_constant (Pmode, to, update_sp_offset);
+ return plus_constant (Pmode, to, note_spoff (update_sp_offset));
return to;
}
else if (update_p)
@@ -385,7 +392,8 @@ lra_eliminate_regs_1 (rtx_insn *insn, rtx x, machine_mode
mem_mode,
ep->offset
- (insn != NULL_RTX
&& ep->to_rtx == stack_pointer_rtx
- ? lra_get_insn_recog_data (insn)->sp_offset
+ ? note_spoff (lra_get_insn_recog_data
+ (insn)->sp_offset)
: 0));
else
return to;
@@ -402,19 +410,18 @@ lra_eliminate_regs_1 (rtx_insn *insn, rtx x, machine_mode
mem_mode,
poly_int64 offset, curr_offset;
rtx to = subst_p ? ep->to_rtx : ep->from_rtx;
- if (ep->to_rtx == stack_pointer_rtx && ep->from ==
FRAME_POINTER_REGNUM)
- elimination_fp2sp_occured_p = true;
-
if (! update_p && ! full_p)
return simplify_gen_binary (PLUS, Pmode, to, XEXP (x, 1));
if (maybe_ne (update_sp_offset, 0))
- offset = ep->to_rtx == stack_pointer_rtx ? update_sp_offset : 0;
+ offset = (ep->to_rtx == stack_pointer_rtx
+ ? note_spoff (update_sp_offset)
+ : 0);
else
offset = (update_p
? ep->offset - ep->previous_offset : ep->offset);
if (full_p && insn != NULL_RTX && ep->to_rtx == stack_pointer_rtx)
- offset -= lra_get_insn_recog_data (insn)->sp_offset;
+ offset -= note_spoff (lra_get_insn_recog_data
(insn)->sp_offset);
if (poly_int_rtx_p (XEXP (x, 1), &curr_offset)
&& known_eq (curr_offset, -offset))
return to;
@@ -465,15 +472,13 @@ lra_eliminate_regs_1 (rtx_insn *insn, rtx x, machine_mode
mem_mode,
{
rtx to = subst_p ? ep->to_rtx : ep->from_rtx;
- if (ep->to_rtx == stack_pointer_rtx && ep->from ==
FRAME_POINTER_REGNUM)
- elimination_fp2sp_occured_p = true;
-
if (maybe_ne (update_sp_offset, 0))
{
if (ep->to_rtx == stack_pointer_rtx)
return plus_constant (Pmode,
gen_rtx_MULT (Pmode, to, XEXP (x, 1)),
- update_sp_offset * INTVAL (XEXP (x, 1)));
+ note_spoff (update_sp_offset)
+ * INTVAL (XEXP (x, 1)));
return gen_rtx_MULT (Pmode, to, XEXP (x, 1));
}
else if (update_p)
@@ -486,7 +491,7 @@ lra_eliminate_regs_1 (rtx_insn *insn, rtx x, machine_mode
mem_mode,
poly_int64 offset = ep->offset;
if (insn != NULL_RTX && ep->to_rtx == stack_pointer_rtx)
- offset -= lra_get_insn_recog_data (insn)->sp_offset;
+ offset -= note_spoff (lra_get_insn_recog_data
(insn)->sp_offset);
return
plus_constant (Pmode,
gen_rtx_MULT (Pmode, to, XEXP (x, 1)),
@@ -1213,8 +1218,7 @@ update_reg_eliminate (bitmap insns_with_changed_offsets)
pointer elimination the condition is a bit relaxed and we just
require
that actual elimination has not been done yet. */
gcc_assert (ep->to_rtx != stack_pointer_rtx
- || (ep->from == FRAME_POINTER_REGNUM
- && !elimination_fp2sp_occured_p)
+ || !elimination_2sp_occurred_p
|| (ep->from < FIRST_PSEUDO_REGISTER
&& fixed_regs [ep->from]));
@@ -1429,7 +1433,7 @@ lra_update_fp2sp_elimination (int *spilled_pseudos)
if (frame_pointer_needed || !targetm.frame_pointer_required ())
return 0;
- gcc_assert (!elimination_fp2sp_occured_p);
+ gcc_assert (!elimination_2sp_occurred_p);
ep = elimination_map[FRAME_POINTER_REGNUM];
if (ep->to == STACK_POINTER_REGNUM)
{
@@ -1499,7 +1503,7 @@ lra_eliminate (bool final_p, bool first_p)
if (first_p)
{
- elimination_fp2sp_occured_p = false;
+ elimination_2sp_occurred_p = false;
init_elimination ();
}
