| Message ID | 87pnbztqru.fsf@euler.schwinge.homeip.net |
|---|---|
| State | New |
| Headers | show |
| Series | [rtl] Harden 'set_noop_p' for non-constant selectors [PR94279] (was: [Patch, RTL] Eliminate redundant vec_select moves) | expand |
On 22/04/2020 17:43, Thomas Schwinge wrote: > In <https://gcc.gnu.org/PR94279> "[amdgcn] internal compiler error: RTL > check: expected code 'const_int', have 'reg' in rtx_to_poly_int64, at > rtl.h:2379", we recently found that that it's wrong to expect constant > selectors, at least in the current code and its usage context. (Thanks, > Richard Biener for the guidance!) Not too many actually, but of course, > this code has seen some changes since 2013-12-04 (for example, r261530 > "Use poly_int rtx accessors instead of hwi accessors"), and also the > context may have changed that it's being used in -- so, I'm not sure > whether the original code (as quoted above) is actually buggy already, > but it already does contain the pattern that 'INTVAL' is used on > something without making sure that we're actually dealing with a constant > selector. (Has that maybe have been an impossible scenario back then?) I think it was impossible. See https://gcc.gnu.org/legacy-ml/gcc-patches/2018-09/msg00273.html > Then, should this also be backported to release branches? GCC 9: same > patch as for master branch. GCC 8: pre poly_int, so only need to guard > 'INTVAL' (by 'CONST_INT_P', right?). Or, is that not worth it, given > that nobody found this to be a problem until now (as far as I know), > and/or it's maybe really specific to (or, exposed by) AMD GCN's vector > instructions? (For AMD GCN offloading, we only care about master > branch.) I don't think it's needed prior to GCC 9, and then only for amdgcn which was probably not widely used. Andrew
Andrew Stubbs <ams@codesourcery.com> writes: > On 22/04/2020 17:43, Thomas Schwinge wrote: >> In <https://gcc.gnu.org/PR94279> "[amdgcn] internal compiler error: RTL >> check: expected code 'const_int', have 'reg' in rtx_to_poly_int64, at >> rtl.h:2379", we recently found that that it's wrong to expect constant >> selectors, at least in the current code and its usage context. (Thanks, >> Richard Biener for the guidance!) Not too many actually, but of course, >> this code has seen some changes since 2013-12-04 (for example, r261530 >> "Use poly_int rtx accessors instead of hwi accessors"), and also the >> context may have changed that it's being used in -- so, I'm not sure >> whether the original code (as quoted above) is actually buggy already, >> but it already does contain the pattern that 'INTVAL' is used on >> something without making sure that we're actually dealing with a constant >> selector. (Has that maybe have been an impossible scenario back then?) > > I think it was impossible. See > https://gcc.gnu.org/legacy-ml/gcc-patches/2018-09/msg00273.html Ah! Thanks for the link. >> Then, should this also be backported to release branches? GCC 9: same >> patch as for master branch. GCC 8: pre poly_int, so only need to guard >> 'INTVAL' (by 'CONST_INT_P', right?). Or, is that not worth it, given >> that nobody found this to be a problem until now (as far as I know), >> and/or it's maybe really specific to (or, exposed by) AMD GCN's vector >> instructions? (For AMD GCN offloading, we only care about master >> branch.) > > I don't think it's needed prior to GCC 9, and then only for amdgcn which > was probably not widely used. Based on that, OK for master and GCC 9. Thanks, Richard
Hi! On 2020-04-22T18:23:24+0100, Richard Sandiford <richard.sandiford@arm.com> wrote: > Andrew Stubbs <ams@codesourcery.com> writes: >> On 22/04/2020 17:43, Thomas Schwinge wrote: >>> In <https://gcc.gnu.org/PR94279> "[amdgcn] internal compiler error: RTL >>> check: expected code 'const_int', have 'reg' in rtx_to_poly_int64, at >>> rtl.h:2379", we recently found that that it's wrong to expect constant >>> selectors, at least in the current code and its usage context. (Thanks, >>> Richard Biener for the guidance!) Not too many actually, but of course, >>> this code has seen some changes since 2013-12-04 (for example, r261530 >>> "Use poly_int rtx accessors instead of hwi accessors"), and also the >>> context may have changed that it's being used in -- so, I'm not sure >>> whether the original code (as quoted above) is actually buggy already, >>> but it already does contain the pattern that 'INTVAL' is used on >>> something without making sure that we're actually dealing with a constant >>> selector. (Has that maybe have been an impossible scenario back then?) >> >> I think it was impossible. See >> https://gcc.gnu.org/legacy-ml/gcc-patches/2018-09/msg00273.html > > Ah! Thanks for the link. Many thanks indeed! That gives confidence why we're running into this problem just now, for GCN target only -- Tejas' original patch thus is not to blame at all, good. (..., and hopefully we won't find much more fall-out due to the GCN target doing away with the constant 'vec_select' restriction...) >>> Then, should this also be backported to release branches? GCC 9: same >>> patch as for master branch. GCC 8: pre poly_int, so only need to guard >>> 'INTVAL' (by 'CONST_INT_P', right?). Or, is that not worth it, given >>> that nobody found this to be a problem until now (as far as I know), >>> and/or it's maybe really specific to (or, exposed by) AMD GCN's vector >>> instructions? (For AMD GCN offloading, we only care about master >>> branch.) >> >> I don't think it's needed prior to GCC 9, and then only for amdgcn which >> was probably not widely used. > > Based on that, OK for master and GCC 9. Thanks for the quick review. I'll later see about backporting for GCC 9. For now pushed to master branch in commit f2c2eaaf8fb5c66ae372bb526b2b2fe67a9c5c39 "[rtl] Harden 'set_noop_p' for non-constant selectors [PR94279]", see attached. Grüße Thomas ----------------- Mentor Graphics (Deutschland) GmbH, Arnulfstraße 201, 80634 München / Germany Registergericht München HRB 106955, Geschäftsführer: Thomas Heurung, Alexander Walter
From 3546ac8ef47cf67570834e5a70614907bef40304 Mon Sep 17 00:00:00 2001 From: Thomas Schwinge <thomas@codesourcery.com> Date: Wed, 22 Apr 2020 16:58:44 +0200 Subject: [PATCH] [rtl] Harden 'set_noop_p' for non-constant selectors [PR94279] --- gcc/rtlanal.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/gcc/rtlanal.c b/gcc/rtlanal.c index c7ab86e228b1..0ebde7622db6 100644 --- a/gcc/rtlanal.c +++ b/gcc/rtlanal.c @@ -1631,12 +1631,18 @@ set_noop_p (const_rtx set) int i; rtx par = XEXP (src, 1); rtx src0 = XEXP (src, 0); - poly_int64 c0 = rtx_to_poly_int64 (XVECEXP (par, 0, 0)); + poly_int64 c0; + if (!poly_int_rtx_p (XVECEXP (par, 0, 0), &c0)) + return 0; poly_int64 offset = GET_MODE_UNIT_SIZE (GET_MODE (src0)) * c0; for (i = 1; i < XVECLEN (par, 0); i++) - if (maybe_ne (rtx_to_poly_int64 (XVECEXP (par, 0, i)), c0 + i)) - return 0; + { + poly_int64 c0i; + if (!poly_int_rtx_p (XVECEXP (par, 0, i), &c0i) + || maybe_ne (c0i, c0 + i)) + return 0; + } return REG_CAN_CHANGE_MODE_P (REGNO (dst), GET_MODE (src0), GET_MODE (dst)) && simplify_subreg_regno (REGNO (src0), GET_MODE (src0), -- 2.25.1