Hi, Jeff, Sorry for the late reply due to thanksgiving long weekend.
> On Nov 25, 2020, at 1:37 PM, Jeff Law <l...@redhat.com> wrote: > > > > On 11/19/20 8:59 AM, Qing Zhao via Gcc-patches wrote: >> Hi, >> >> PR97777 - ICE: in df_refs_verify, at df-scan.c:3991 with -O >> -ffinite-math-only -fzero-call-used-regs=all >> >> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97777 >> >> Is a bug triggered by the new pass zero-call-used-regs, however, it’s an old >> bug in the pass “reg-stack”. >> This pass does not correctly maintain the df information after >> transformation. >> >> Since the transformation is reg-stack pass is quite complicate, involving >> both instruction changes and control >> Flow changes, I called “df_insn_rescan_all” after the transformation is done. >> >> The patch has been tested with bootstrap with >> --enable-checking=yes,rtl,df,extra, no regression. >> >> Okay for commit? >> >> Qing >> >> From c2573c6c8552b7b4c2eedb0684ce48b5c11436ec Mon Sep 17 00:00:00 2001 >> From: qing zhao <qinz...@gcc.gnu.org> >> Date: Thu, 19 Nov 2020 16:46:50 +0100 >> Subject: [PATCH] rtl-optimization: Fix data flow maintenance bug in >> reg-stack.c [pr97777] >> >> reg-stack pass does not maintain the data flow information correctly. >> call df_insn_rescan_all after the transformation is done. >> >> gcc/ >> PR rtl-optimization/97777 >> * reg-stack.c (rest_of_handle_stack_regs): call >> df_insn_rescan_all if reg_to_stack return true. >> >> gcc/testsuite/ >> PR rtl-optimization/97777 >> * gcc.target/i386/pr97777.c: New test. > I'd like to see more analysis here. > > ie, precisely what data is out of date and why? For the simple testing case, what happened is, for the insn #6: (gdb) call debug_rtx(insn) (insn 6 26 7 2 (set (reg:XF 8 st [84]) (reg:XF 9 st(1) [85])) "t.c":4:10 134 {*movxf_internal} (expr_list:REG_EQUAL (const_double:XF 0.0 [0x0.0p+0]) (nil))) After the following statement in reg-stack.c: 3080 control_flow_insn_deleted |= subst_stack_regs (insn, ®stack); This insn # 6 becomes: (gdb) call debug_rtx(insn) (insn 6 26 7 2 (set (reg:XF 8 st) (reg:XF 8 st)) "t.c":4:10 134 {*movxf_internal} (expr_list:REG_EQUAL (const_double:XF 0.0 [0x0.0p+0]) (nil))) However, there is no any df maintenance routine (for example, df_insn_rescan, etc) is called for this changed insn. As I checked, the transformation for this pass “stack” is quite complicated. In addition to the above register replacement, New insns might be inserted, and control flow might be changed, but for most of the transformations applied in this pass, There is no corresponding df maintenance routine is added for deferred df rescanning. Therefore, I called the “df_insn_rescan_all” after the whole transformation is done to maintain the df information. Another solution is to check all the details of the transformations of this pass, and add the df maintenance routine case by case for each of the transformation. Since the transformation of the pass “stack” is quite extensive and complicate, I feel that calling “df_insn_rescan_all” might be a better solution. Let me know your suggestions. thanks. Qing > > Jeff
