Hi, Just check in to see whether you have any comments and suggestions on this:
FYI, I have been continue with Approach D implementation since last week: D. Adding calls to .DEFFERED_INIT during gimplification, expand the .DEFFERED_INIT during expand to real initialization. Adjusting uninitialized pass with the new refs with “.DEFFERED_INIT”. For the remaining work of Approach D: ** complete the implementation of -ftrivial-auto-var-init=pattern; ** complete the implementation of uninitialized warnings maintenance work for D. I have completed the uninitialized warnings maintenance work for D. And finished partial of the -ftrivial-auto-var-init=pattern implementation. The following are remaining work of Approach D: ** -ftrivial-auto-var-init=pattern for VLA; **add a new attribute for variable: __attribute((uninitialized) the marked variable is uninitialized intentionaly for performance purpose. ** adding complete testing cases; Please let me know if you have any objection on my current decision on implementing approach D. Thanks a lot for your help. Qing > On Jan 5, 2021, at 1:05 PM, Qing Zhao via Gcc-patches > <gcc-patches@gcc.gnu.org> wrote: > > Hi, > > This is an update for our previous discussion. > > 1. I implemented the following two different implementations in the latest > upstream gcc: > > A. Adding real initialization during gimplification, not maintain the > uninitialized warnings. > > D. Adding calls to .DEFFERED_INIT during gimplification, expand the > .DEFFERED_INIT during expand to > real initialization. Adjusting uninitialized pass with the new refs with > “.DEFFERED_INIT”. > > Note, in this initial implementation, > ** I ONLY implement -ftrivial-auto-var-init=zero, the implementation of > -ftrivial-auto-var-init=pattern > is not done yet. Therefore, the performance data is only about > -ftrivial-auto-var-init=zero. > > ** I added an temporary option -fauto-var-init-approach=A|B|C|D to > choose implementation A or D for > runtime performance study. > ** I didn’t finish the uninitialized warnings maintenance work for D. > (That might take more time than I expected). > > 2. I collected runtime data for CPU2017 on a x86 machine with this new gcc > for the following 3 cases: > > no: default. (-g -O2 -march=native ) > A: default + -ftrivial-auto-var-init=zero -fauto-var-init-approach=A > D: default + -ftrivial-auto-var-init=zero -fauto-var-init-approach=D > > And then compute the slowdown data for both A and D as following: > > benchmarks A / no D /no > > 500.perlbench_r 1.25% 1.25% > 502.gcc_r 0.68% 1.80% > 505.mcf_r 0.68% 0.14% > 520.omnetpp_r 4.83% 4.68% > 523.xalancbmk_r 0.18% 1.96% > 525.x264_r 1.55% 2.07% > 531.deepsjeng_ 11.57% 11.85% > 541.leela_r 0.64% 0.80% > 557.xz_ -0.41% -0.41% > > 507.cactuBSSN_r 0.44% 0.44% > 508.namd_r 0.34% 0.34% > 510.parest_r 0.17% 0.25% > 511.povray_r 56.57% 57.27% > 519.lbm_r 0.00% 0.00% > 521.wrf_r -0.28% -0.37% > 526.blender_r 16.96% 17.71% > 527.cam4_r 0.70% 0.53% > 538.imagick_r 2.40% 2.40% > 544.nab_r 0.00% -0.65% > > avg 5.17% 5.37% > > From the above data, we can see that in general, the runtime performance > slowdown for > implementation A and D are similar for individual benchmarks. > > There are several benchmarks that have significant slowdown with the new > added initialization for both > A and D, for example, 511.povray_r, 526.blender_, and 531.deepsjeng_r, I will > try to study a little bit > more on what kind of new initializations introduced such slowdown. > > From the current study so far, I think that approach D should be good enough > for our final implementation. > So, I will try to finish approach D with the following remaining work > > ** complete the implementation of -ftrivial-auto-var-init=pattern; > ** complete the implementation of uninitialized warnings maintenance > work for D. > > > Let me know if you have any comments and suggestions on my current and future > work. > > Thanks a lot for your help. > > Qing > >> On Dec 9, 2020, at 10:18 AM, Qing Zhao via Gcc-patches >> <gcc-patches@gcc.gnu.org> wrote: >> >> The following are the approaches I will implement and compare: >> >> Our final goal is to keep the uninitialized warning and minimize the >> run-time performance cost. >> >> A. Adding real initialization during gimplification, not maintain the >> uninitialized warnings. >> B. Adding real initialization during gimplification, marking them with >> “artificial_init”. >> Adjusting uninitialized pass, maintaining the annotation, making sure the >> real init not >> Deleted from the fake init. >> C. Marking the DECL for an uninitialized auto variable as >> “no_explicit_init” during gimplification, >> maintain this “no_explicit_init” bit till after >> pass_late_warn_uninitialized, or till pass_expand, >> add real initialization for all DECLs that are marked with >> “no_explicit_init”. >> D. Adding .DEFFERED_INIT during gimplification, expand the .DEFFERED_INIT >> during expand to >> real initialization. Adjusting uninitialized pass with the new refs with >> “.DEFFERED_INIT”. >> >> >> In the above, approach A will be the one that have the minimum run-time >> cost, will be the base for the performance >> comparison. >> >> I will implement approach D then, this one is expected to have the most >> run-time overhead among the above list, but >> Implementation should be the cleanest among B, C, D. Let’s see how much more >> performance overhead this approach >> will be. If the data is good, maybe we can avoid the effort to implement B, >> and C. >> >> If the performance of D is not good, I will implement B or C at that time. >> >> Let me know if you have any comment or suggestions. >> >> Thanks. >> >> Qing >
