|
|
@@ -1,107 +0,0 @@
|
|
|
-From 840e53f15468b1e808386c6190d7f59227b85495 Mon Sep 17 00:00:00 2001
|
|
|
-Message-ID: <840e53f15468b1e808386c6190d7f59227b85495.1747165068.git.mschiffer@universe-factory.net>
|
|
|
-From: Denis Chertykov <[email protected]>
|
|
|
-Date: Thu, 17 Oct 2024 11:12:38 +0400
|
|
|
-Subject: [PATCH] Reuse scratch registers generated by LRA
|
|
|
-
|
|
|
-Test file: udivmoddi.c
|
|
|
-problem insn: 484
|
|
|
-
|
|
|
-Before LRA pass we have:
|
|
|
-(insn 484 483 485 72 (parallel [
|
|
|
- (set (reg/v:SI 143 [ __q1 ])
|
|
|
- (plus:SI (reg/v:SI 143 [ __q1 ])
|
|
|
- (const_int -2 [0xfffffffffffffffe])))
|
|
|
- (clobber (scratch:QI))
|
|
|
- ]) "udivmoddi.c":163:405 discrim 5 186 {addsi3}
|
|
|
- (nil))
|
|
|
-
|
|
|
-LRA substitute all scratches with new pseudos, so we have:
|
|
|
-(insn 484 483 485 72 (parallel [
|
|
|
- (set (reg/v:SI 143 [ __q1 ])
|
|
|
- (plus:SI (reg/v:SI 143 [ __q1 ])
|
|
|
- (const_int -2 [0xfffffffffffffffe])))
|
|
|
- (clobber (reg:QI 619))
|
|
|
- ]) "/mnt/d/avr-lra/udivmoddi.c":163:405 discrim 5 186 {addsi3}
|
|
|
- (expr_list:REG_UNUSED (reg:QI 619)
|
|
|
- (nil)))
|
|
|
-
|
|
|
-Pseudo 619 is a special scratch register generated by LRA which is marked in `scratch_bitmap' and can be tested by call `ira_former_scratch_p(regno)'.
|
|
|
-
|
|
|
-In dump file (udivmoddi.c.317r.reload) we have:
|
|
|
- Creating newreg=619
|
|
|
-Removing SCRATCH to p619 in insn #484 (nop 3)
|
|
|
-rescanning insn with uid = 484.
|
|
|
-
|
|
|
-After that LRA tries to spill (reg:QI 619)
|
|
|
-It's a bug because (reg:QI 619) is an output scratch register which is already something like spill register.
|
|
|
-
|
|
|
-Fragment from udivmoddi.c.317r.reload:
|
|
|
- Choosing alt 2 in insn 484: (0) r (1) 0 (2) nYnn (3) &d {addsi3}
|
|
|
- Creating newreg=728 from oldreg=619, assigning class LD_REGS to r728
|
|
|
-
|
|
|
-IMHO: the bug is in lra-constraints.cc in function `get_reload_reg'
|
|
|
-fragment of `get_reload_reg':
|
|
|
- if (type == OP_OUT)
|
|
|
- {
|
|
|
- /* Output reload registers tend to start out with a conservative
|
|
|
- choice of register class. Usually this is ALL_REGS, although
|
|
|
- a target might narrow it (for performance reasons) through
|
|
|
- targetm.preferred_reload_class. It's therefore quite common
|
|
|
- for a reload instruction to require a more restrictive class
|
|
|
- than the class that was originally assigned to the reload register.
|
|
|
-
|
|
|
- In these situations, it's more efficient to refine the choice
|
|
|
- of register class rather than create a second reload register.
|
|
|
- This also helps to avoid cycling for registers that are only
|
|
|
- used by reload instructions. */
|
|
|
- if (REG_P (original)
|
|
|
- && (int) REGNO (original) >= new_regno_start
|
|
|
- && INSN_UID (curr_insn) >= new_insn_uid_start
|
|
|
-__________________________________^^
|
|
|
- && in_class_p (original, rclass, &new_class, true))
|
|
|
- {
|
|
|
- unsigned int regno = REGNO (original);
|
|
|
- if (lra_dump_file != NULL)
|
|
|
- {
|
|
|
- fprintf (lra_dump_file, " Reuse r%d for output ", regno);
|
|
|
- dump_value_slim (lra_dump_file, original, 1);
|
|
|
- }
|
|
|
-
|
|
|
-This condition incorrectly limits register reuse to ONLY newly generated instructions.
|
|
|
-i.e. LRA can reuse registers only from insns generated by himself.
|
|
|
-
|
|
|
-IMHO:It's wrong.
|
|
|
-Scratch registers generated by LRA also have to be reused.
|
|
|
-
|
|
|
-The patch is very simple.
|
|
|
-On x86_64, it bootstraps+regtests fine.
|
|
|
-
|
|
|
-gcc/
|
|
|
- PR target/116550
|
|
|
- PR target/119340
|
|
|
- * lra-constraints.cc (get_reload_reg): Reuse scratch registers
|
|
|
- generated by LRA.
|
|
|
-
|
|
|
-(cherry picked from commit e7393cbb5f2cae50b42713e71984064073aa378a)
|
|
|
----
|
|
|
- gcc/lra-constraints.cc | 3 ++-
|
|
|
- 1 file changed, 2 insertions(+), 1 deletion(-)
|
|
|
-
|
|
|
-diff --git a/gcc/lra-constraints.cc b/gcc/lra-constraints.cc
|
|
|
-index 10e3d4e4097..d44c73e59c8 100644
|
|
|
---- a/gcc/lra-constraints.cc
|
|
|
-+++ b/gcc/lra-constraints.cc
|
|
|
-@@ -676,7 +676,8 @@ get_reload_reg (enum op_type type, machine_mode mode, rtx original,
|
|
|
- used by reload instructions. */
|
|
|
- if (REG_P (original)
|
|
|
- && (int) REGNO (original) >= new_regno_start
|
|
|
-- && INSN_UID (curr_insn) >= new_insn_uid_start
|
|
|
-+ && (INSN_UID (curr_insn) >= new_insn_uid_start
|
|
|
-+ || ira_former_scratch_p (REGNO (original)))
|
|
|
- && in_class_p (original, rclass, &new_class, true))
|
|
|
- {
|
|
|
- unsigned int regno = REGNO (original);
|
|
|
---
|
|
|
-2.49.0
|
|
|
-
|
Shiji Yang