[Bug rtl-optimization/61605] Potential optimization: Keep unclobbered argument registers live across function calls
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61605 --- Comment #10 from vries at gcc dot gnu.org --- Author: vries Date: Fri Oct 17 06:36:45 2014 New Revision: 216365 URL: https://gcc.gnu.org/viewcvs?rev=216365root=gccview=rev Log: Use fuse-caller-save info in cprop-hardreg 2014-10-17 Tom de Vries t...@codesourcery.com PR rtl-optimization/61605 * regcprop.c (copyprop_hardreg_forward_1): Use regs_invalidated_by_this_call instead of regs_invalidated_by_call. * gcc.target/i386/fuse-caller-save.c: Update addition check. Add movl absence check. Modified: trunk/gcc/ChangeLog trunk/gcc/regcprop.c trunk/gcc/testsuite/ChangeLog trunk/gcc/testsuite/gcc.target/i386/fuse-caller-save.c
[Bug rtl-optimization/61605] Potential optimization: Keep unclobbered argument registers live across function calls
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61605 --- Comment #9 from vries at gcc dot gnu.org --- Author: vries Date: Fri Oct 17 06:36:35 2014 New Revision: 216364 URL: https://gcc.gnu.org/viewcvs?rev=216364root=gccview=rev Log: Handle copy cycles in pass_cprop_hardreg 2014-10-17 Tom de Vries t...@codesourcery.com PR rtl-optimization/61605 * regcprop.c (copyprop_hardreg_forward_1): Add copy_p and noop_p. Don't notice stores for noops. Don't regard noops as copies. Modified: trunk/gcc/ChangeLog trunk/gcc/regcprop.c
[Bug rtl-optimization/61605] Potential optimization: Keep unclobbered argument registers live across function calls
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61605 vries at gcc dot gnu.org changed: What|Removed |Added Keywords||missed-optimization Status|ASSIGNED|RESOLVED Resolution|--- |FIXED --- Comment #11 from vries at gcc dot gnu.org --- Patches committed, test-case updated. Resolving as fixed.
[Bug rtl-optimization/61605] Potential optimization: Keep unclobbered argument registers live across function calls
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61605 vries at gcc dot gnu.org changed: What|Removed |Added Keywords||patch --- Comment #8 from vries at gcc dot gnu.org --- Patches submitted at: https://gcc.gnu.org/ml/gcc-patches/2014-10/msg01513.html https://gcc.gnu.org/ml/gcc-patches/2014-10/msg01514.html
[Bug rtl-optimization/61605] Potential optimization: Keep unclobbered argument registers live across function calls
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61605 --- Comment #6 from vries at gcc dot gnu.org --- Created attachment 33618 -- https://gcc.gnu.org/bugzilla/attachment.cgi?id=33618action=edit [1/2] Use fuse-caller-save-info in cprop-hardreg
[Bug rtl-optimization/61605] Potential optimization: Keep unclobbered argument registers live across function calls
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61605 --- Comment #7 from vries at gcc dot gnu.org --- Created attachment 33619 -- https://gcc.gnu.org/bugzilla/attachment.cgi?id=33619action=edit [2/2] Don't regard a copy with identical src and dest as killing dest This patch adds handling of copies with identical source and destination register in copyprop_hardreg_forward_1. Using this patch series we get the desired code.
[Bug rtl-optimization/61605] Potential optimization: Keep unclobbered argument registers live across function calls
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61605 vries at gcc dot gnu.org changed: What|Removed |Added Status|NEW |ASSIGNED Assignee|unassigned at gcc dot gnu.org |vries at gcc dot gnu.org
[Bug rtl-optimization/61605] Potential optimization: Keep unclobbered argument registers live across function calls
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61605 vries at gcc dot gnu.org changed: What|Removed |Added Status|UNCONFIRMED |NEW Last reconfirmed||2014-09-29 CC||vries at gcc dot gnu.org Ever confirmed|0 |1 --- Comment #4 from vries at gcc dot gnu.org --- If a function is known to not clobber an argument register then the caller shouldn't have to save/reload that register across the function call. If a function is known to not clobber an call_used_reg then the caller can use it as a non-call_used_reg across the function call. This diff shows the example with -fno-use-caller-save vs -fuse-caller-save: ... foo: .LFB1: .cfi_startproc -pushq%rbx -.cfi_def_cfa_offset 16 -.cfi_offset 3, -16 -movl%edi, %ebx +movl%edi, %edx callbar -addl%ebx, %eax -popq%rbx -.cfi_def_cfa_offset 8 +addl%edx, %eax ret .cfi_endproc .LFE1: ... -fuse-caller-save removes the entry/exit save/restore pair 'pushq %rbx'/'popq %rbx'. The 'movl %edi, %edx' is indeed non-optimal, but it's not a 'save' in the sense of save/restore pair generated at function entry/exit or around function calls. It's a copy at function entry of a hard reg argumument to a pseudo reg, generated at expand, which is followed by a copy of the pseudo reg to the same register to set the argument for the function call: ... (insn 2 4 3 2 (set (reg/v:SI 86 [ yD.1755 ]) (reg:SI 5 di [ yD.1755 ])) test.c:9 -1 (nil)) (note 3 2 6 2 NOTE_INSN_FUNCTION_BEG) (insn 6 3 7 2 (set (reg:SI 5 di) (reg/v:SI 86 [ yD.1755 ])) test.c:10 -1 (nil)) ... The second insn is removed in pass_fast_rtl_dce. The reg-alloc choiche for pseudo 86 in the first insn is dx, and the insn remains. I think there could be two ways to address this: 1. Teach a pass after ira, like pass_cprop_hardreg or pass_gcse2 to use the information collected by fuse-calller-save. 2. Teach ira to prefer the dx to di in this case. My guess would be pass_cprop_hardreg.
[Bug rtl-optimization/61605] Potential optimization: Keep unclobbered argument registers live across function calls
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61605
--- Comment #5 from vries at gcc dot gnu.org ---
Created attachment 33610
-- https://gcc.gnu.org/bugzilla/attachment.cgi?id=33610action=edit
proof-of-concept patch
Using this proof-of-concept patch, we manage to get the desired code. The patch
uses the fuse-caller-save information in cprop-hardreg, and runs cprop-hardreg
one more time, after pass_fast_rtl_dce.
Obviously it's not desirable to run cprop-hardreg twice. But the pass has
problems with this code:
...
(insn 2 18 3 2 (set (reg/v:SI 1 dx [orig:86 yD.1749 ] [86])
(reg:SI 5 di [ yD.1749 ])) test.c:9 90 {*movsi_internal}
(expr_list:REG_DEAD (reg:SI 5 di [ yD.1749 ])
(nil)))
(note 3 2 6 2 NOTE_INSN_FUNCTION_BEG)
(insn 6 3 7 2 (set (reg:SI 5 di)
(reg/v:SI 1 dx [orig:86 yD.1749 ] [86])) test.c:10 90 {*movsi_internal}
(nil))
...
The first time cprop-hardreg runs, it manages to propagate the first copy (insn
2) to the second (insn 6):
...
rescanning insn with uid = 6.
insn 6: replaced reg 1 with 5
...
So insn 6 looks like:
...
(insn 6 3 7 2 (set (reg:SI 5 di)
(reg:SI 5 di [orig:86 yD.1749 ] [86])) test.c:10 90 {*movsi_internal}
(nil))
...
That insn is remove by pass_fast_rtl_dce:
...
DCE: Deleting insn 6
deleting insn with uid = 6.
...
And only the second time we run it, we propagate the first copy to the add:
...
insn 9: replaced reg 1 with 5
rescanning insn with uid = 9.
...
which then looks like this:
...
(insn 9 7 15 2 (parallel [
(set (reg:SI 0 ax [orig:87 D.1767 ] [87])
(plus:SI (reg:SI 0 ax [orig:83 D.1767 ] [83])
(reg:SI 5 di [orig:86 yD.1749 ] [86])))
(clobber (reg:CC 17 flags))
]) test.c:10 220 {*addsi_1}
(expr_list:REG_DEAD (reg/v:SI 1 dx [orig:86 yD.1749 ] [86])
(expr_list:REG_UNUSED (reg:CC 17 flags)
(nil
...
That leaves insn 2 dead, which is deleted by dce during sched2:
...
DCE: Deleting insn 2
deleting insn with uid = 2.
...
I'm not sure yet why the cprop-hardreg doesn't work for both cases the first
time, but it's probably that the store to di by insn 6 is registered as a kill
by cprop-hardreg, not taking into account that it's the same value.
[Bug rtl-optimization/61605] Potential optimization: Keep unclobbered argument registers live across function calls
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61605 Andi Kleen andi-gcc at firstfloor dot org changed: What|Removed |Added CC||andi-gcc at firstfloor dot org, ||tom at codesourcery dot com --- Comment #1 from Andi Kleen andi-gcc at firstfloor dot org --- This is in theory implemented in mainline with -fuse-caller-save It doesn't seem to work for me though. I also didn't see the option doing anything on a larger program.
[Bug rtl-optimization/61605] Potential optimization: Keep unclobbered argument registers live across function calls
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61605 Andrew Pinski pinskia at gcc dot gnu.org changed: What|Removed |Added Target||x86_64-*-* --- Comment #2 from Andrew Pinski pinskia at gcc dot gnu.org --- (In reply to Andi Kleen from comment #1) This is in theory implemented in mainline with -fuse-caller-save It doesn't seem to work for me though. I also didn't see the option doing anything on a larger program. Most likely because it is not fully implemented for x86 :).
[Bug rtl-optimization/61605] Potential optimization: Keep unclobbered argument registers live across function calls
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61605 --- Comment #3 from Andi Kleen andi-gcc at firstfloor dot org --- It was supposed to be enabled with Date: Fri May 30 11:39:49 2014 + -fuse-caller-save - Enable for i386 2014-05-30 Tom de Vries t...@codesourcery.com * config/i386/i386.c (TARGET_CALL_FUSAGE_CONTAINS_NON_CALLEE_CLOBBERS): Redefine as true. * gcc.target/i386/fuse-caller-save.c: New test. * gcc.dg/ira-shrinkwrap-prep-1.c: Run with -fno-use-caller-save. * gcc.dg/ira-shrinkwrap-prep-2.c: Same. git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@211078 138bc75d-0d04-0410-961f-82ee72b054a4
