https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118615
--- Comment #26 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
So, I'd at least suggest:
--- gcc/lra-constraints.cc.jj 2025-02-01 00:47:07.926078697 +0100
+++ gcc/lra-constraints.cc 2025-03-19 18:54:08.035516274 +0100
@@ -152,6 +152,9 @@ static machine_mode curr_operand_mode[MA
(e.g. constant) and whose subreg is given operand of the current
insn. VOIDmode in all other cases. */
static machine_mode original_subreg_reg_mode[MAX_RECOG_OPERANDS];
+/* The first call insn after curr_insn within the EBB during inherit_in_ebb
+ or NULL outside of that function. */
+static rtx_insn *first_call_insn;
@@ -6373,12 +6376,26 @@ split_reg (bool before_p, int original_r
lra_process_new_insns (as_a <rtx_insn *> (usage_insn),
after_p ? NULL : restore,
after_p ? restore : NULL,
- call_save_p
- ? "Add reg<-save" : "Add reg<-split");
- lra_process_new_insns (insn, before_p ? save : NULL,
- before_p ? NULL : save,
- call_save_p
- ? "Add save<-reg" : "Add split<-reg");
+ call_save_p ? "Add reg<-save" : "Add reg<-split");
+ if (call_save_p
+ && first_call_insn != NULL
+ && BLOCK_FOR_INSN (first_call_insn) != BLOCK_FOR_INSN (insn))
+ /* PR116028: If original_regno is a pseudo that has been assigned a
+ call-save hard register, then emit the spill insn before the call
+ insn 'first_call_insn' instead of adjacent to 'insn'. If 'insn'
+ and 'first_call_insn' belong to the same EBB but to two separate
+ BBs, and if 'insn' is present in the entry BB, then generating the
+ spill insn in the entry BB can prevent shrink wrap from happening.
+ This is because the spill insn references the stack pointer and
+ hence the prolog gets generated in the entry BB itself. It is
+ also more efficient to generate the spill before
+ 'first_call_insn' as the spill now occurs only in the path
+ containing the call. */
+ lra_process_new_insns (first_call_insn, save, NULL, "Add save<-reg");
+ else
+ lra_process_new_insns (insn, before_p ? save : NULL,
+ before_p ? NULL : save,
+ call_save_p ? "Add save<-reg" : "Add split<-reg");
if (nregs > 1 || original_regno < FIRST_PSEUDO_REGISTER)
/* If we are trying to split multi-register. We should check
conflicts on the next assignment sub-pass. IRA can allocate on
@@ -6862,6 +6879,7 @@ inherit_in_ebb (rtx_insn *head, rtx_insn
last_processed_bb = NULL;
CLEAR_HARD_REG_SET (potential_reload_hard_regs);
live_hard_regs = eliminable_regset | lra_no_alloc_regs;
+ first_call_insn = NULL;
/* We don't process new insns generated in the loop. */
for (curr_insn = tail; curr_insn != PREV_INSN (head); curr_insn = prev_insn)
{
@@ -7074,6 +7092,7 @@ inherit_in_ebb (rtx_insn *head, rtx_insn
last_call_for_abi[callee_abi.id ()] = calls_num;
full_and_partial_call_clobbers
|= callee_abi.full_and_partial_reg_clobbers ();
+ first_call_insn = curr_insn;
if ((cheap = find_reg_note (curr_insn,
REG_RETURNED, NULL_RTX)) != NULL_RTX
&& ((cheap = XEXP (cheap, 0)), true)
@@ -7278,6 +7297,7 @@ inherit_in_ebb (rtx_insn *head, rtx_insn
}
}
}
+ first_call_insn = NULL;
return change_p;
}
But I get the -fcompare-debug failure with that patch on top of trunk on #c23
as well.
I'll keep debugging what went different and why tomorrow.
