On Mon, Feb 8, 2016 at 11:37 AM, Eric Botcazou <ebotca...@adacore.com> wrote: > Hi, > > the Ada runtime fails to build for platforms still using the old SJLJ scheme > because of the new GIMPLE backprop pass (hence it's a regression): > > eric@polaris:~/build/gcc/native> gcc/gnat1 -quiet a-ncelfu.ads -gnatpg -O -I > ~/svn/gcc/gcc/ada/ > a-ngcefu.adb: In function 'Ada.Numerics.Complex_Elementary_Functions.Sqrt': > a-ngcefu.adb:16:4: error: SSA_NAME_OCCURS_IN_ABNORMAL_PHI should be set > for SSA_NAME: _28 in statement: > xr_3(ab) = PHI <xr_22(D)(ab)(2), xr_22(D)(ab)(3), xr_22(D)(ab)(4), _28(5), > _28(6), _28(7), xr_4(ab)(11), xr_4(ab)(12), xr_4(ab)(14), xr_4(ab)(15), > xr_4(ab)(16), xr_4(ab)(17), xr_4(ab)(18), xr_4(ab)(19), xr_4(ab)(20), xr_4(ab) > (21), xr_4(ab)(22), xr_4(ab)(23), xr_4(ab)(24), xr_4(ab)(25), xr_4(ab)(26), > xr_4(ab)(27), xr_4(ab)(28), xr_4(ab)(29), xr_4(ab)(30), xr_4(ab)(32), xr_4(ab) > (34), xr_4(ab)(36), xr_4(ab)(37)> > PHI argument > _28 > for PHI node > xr_3(ab) = PHI <xr_22(D)(ab)(2), xr_22(D)(ab)(3), xr_22(D)(ab)(4), _28(5), > _28(6), _28(7), xr_4(ab)(11), xr_4(ab)(12), xr_4(ab)(14), xr_4(ab)(15), > xr_4(ab)(16), xr_4(ab)(17), xr_4(ab)(18), xr_4(ab)(19), xr_4(ab)(20), xr_4(ab) > (21), xr_4(ab)(22), xr_4(ab)(23), xr_4(ab)(24), xr_4(ab)(25), xr_4(ab)(26), > xr_4(ab)(27), xr_4(ab)(28), xr_4(ab)(29), xr_4(ab)(30), xr_4(ab)(32), xr_4(ab) > (34), xr_4(ab)(36), xr_4(ab)(37)> > +===========================GNAT BUG DETECTED==============================+ > | 6.0.0 20160206 (experimental) [trunk revision 233194] (x86_64-suse-linux) > GCC error:| > | verify_ssa failed | > | Error detected around a-ngcefu.adb:16:4 > > The problem is that the pass propagates the source RHS (_28) of: > > xr_29(ab) = ABS_EXPR <_28>; > > into a PHI note using xr_29 along an AB edge so the above check triggers. > > I think replacing such an AB SSA_NAME is problematic in any case: if the RHS > is not AB, then the check triggers; if the RHS is also AB, then we may create > overlapping live ranges and the compilation will abort later. We can probably > create a new SSA_NAME but it's not really the spirit of the backprop pass and > I'm not sure it's worth the hassle, hence the minimal attached fixlet.
I think the problematic transform is when the replacement happens on a PHI arg with its edge being abnormal only. Thus simply do if (EDGE_PRED (gimple_bb (phi), PHI_ARG_INDEX_FROM_USE (use))->flags & EDGE_ABNORMAL) continue; at the start of the FOR_EACH_PHI_ARG body. Thanks, Richard. > Tested on x86_64-suse-linux, OK for the mainline? > > > 2016-02-08 Eric Botcazou <ebotca...@adacore.com> > > * gimple-ssa-backprop.c (optimize_phi): Do not replace an argument > with SSA_NAME_OCCURS_IN_ABNORMAL_PHI set. > > -- > Eric Botcazou
