The following patch is a fix for PR114810 from LRA side.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114810
The patch was successfully bootstrapped and tested on x86_64, aarch64,
ppc64le.
commit dc859c1fcb6f3ad95022fb078c040907ef361e4c
Author: Vladimir N. Makarov <vmaka...@redhat.com>
Date: Wed May 8 10:39:04 2024 -0400
[PR114810][LRA]: Recognize alternatives with lack of available registers for insn and demote them.
PR114810 was fixed in machine-dependent way. This patch is a fix of
the PR on LRA side. LRA chose alternative with constraints `&r,r,ro`
on i686 when all operands of DImode and there are only 6 available
general regs. The patch recognizes such case and significantly
increase the alternative cost. It does not reject alternative
completely. So the fix is safe but it might not work for all
potentially possible cases of registers lack as register classes can
have any relations including subsets and intersections.
gcc/ChangeLog:
PR target/114810
* lra-constraints.cc (process_alt_operands): Calculate union reg
class for the alternative, peak matched regs and required reload
regs. Recognize alternatives with lack of available registers and
make them costly. Add debug print about this case.
diff --git a/gcc/lra-constraints.cc b/gcc/lra-constraints.cc
index 10e3d4e4097..5b78fd0b7e5 100644
--- a/gcc/lra-constraints.cc
+++ b/gcc/lra-constraints.cc
@@ -2127,6 +2127,8 @@ process_alt_operands (int only_alternative)
/* Numbers of operands which are early clobber registers. */
int early_clobbered_nops[MAX_RECOG_OPERANDS];
enum reg_class curr_alt[MAX_RECOG_OPERANDS];
+ enum reg_class all_this_alternative;
+ int all_used_nregs, all_reload_nregs;
HARD_REG_SET curr_alt_set[MAX_RECOG_OPERANDS];
HARD_REG_SET curr_alt_exclude_start_hard_regs[MAX_RECOG_OPERANDS];
bool curr_alt_match_win[MAX_RECOG_OPERANDS];
@@ -2229,7 +2231,8 @@ process_alt_operands (int only_alternative)
curr_alt_out_sp_reload_p = false;
curr_reuse_alt_p = true;
curr_alt_class_change_p = false;
-
+ all_this_alternative = NO_REGS;
+ all_used_nregs = all_reload_nregs = 0;
for (nop = 0; nop < n_operands; nop++)
{
const char *p;
@@ -2660,6 +2663,15 @@ process_alt_operands (int only_alternative)
/* Record which operands fit this alternative. */
if (win)
{
+ if (early_clobber_p
+ || curr_static_id->operand[nop].type != OP_OUT)
+ {
+ all_used_nregs
+ += ira_reg_class_min_nregs[this_alternative][mode];
+ all_this_alternative
+ = (reg_class_subunion
+ [all_this_alternative][this_alternative]);
+ }
this_alternative_win = true;
if (class_change_p)
{
@@ -2781,7 +2793,19 @@ process_alt_operands (int only_alternative)
& ~((ira_prohibited_class_mode_regs
[this_alternative][mode])
| lra_no_alloc_regs));
- if (hard_reg_set_empty_p (available_regs))
+ if (!hard_reg_set_empty_p (available_regs))
+ {
+ if (early_clobber_p
+ || curr_static_id->operand[nop].type != OP_OUT)
+ {
+ all_reload_nregs
+ += ira_reg_class_min_nregs[this_alternative][mode];
+ all_this_alternative
+ = (reg_class_subunion
+ [all_this_alternative][this_alternative]);
+ }
+ }
+ else
{
/* There are no hard regs holding a value of given
mode. */
@@ -3217,6 +3241,21 @@ process_alt_operands (int only_alternative)
" Cycle danger: overall += LRA_MAX_REJECT\n");
overall += LRA_MAX_REJECT;
}
+ if (all_this_alternative != NO_REGS
+ && all_used_nregs != 0 && all_reload_nregs != 0
+ && (all_used_nregs + all_reload_nregs + 1
+ >= ira_class_hard_regs_num[all_this_alternative]))
+ {
+ if (lra_dump_file != NULL)
+ fprintf
+ (lra_dump_file,
+ " Register starvation: overall += LRA_MAX_REJECT"
+ "(class=%s,avail=%d,used=%d,reload=%d)\n",
+ reg_class_names[all_this_alternative],
+ ira_class_hard_regs_num[all_this_alternative],
+ all_used_nregs, all_reload_nregs);
+ overall += LRA_MAX_REJECT;
+ }
ok_p = true;
curr_alt_dont_inherit_ops_num = 0;
for (nop = 0; nop < early_clobbered_regs_num; nop++)
