[Bug rtl-optimization/88296] New: [9 Regression] Infinite loop in lra_split_hard_reg_for

["asolokha at gmx dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88296

            Bug ID: 88296
           Summary: [9 Regression] Infinite loop in lra_split_hard_reg_for
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Keywords: memory-hog, ra
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: asolokha at gmx dot com
  Target Milestone: ---
            Target: x86_64-unknown-linux-gnu

Created attachment 45134
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=45134&action=edit
The testcase

gcc-9.0.0-alpha20181125 snapshot (r266441) takes indefinite time compiling the
attached snippet w/ -O2 (-O3, -Ofast) -march=core2 -fnon-call-exceptions
-fschedule-insns -fselective-scheduling -funroll-all-loops -fno-caller-saves
-fno-guess-branch-probability -fno-ivopts -fno-rerun-cse-after-loop
-fno-split-wide-types -fno-tree-bit-ccp -fno-tree-coalesce-vars --param
max-completely-peeled-insns=13:

% timeout 10 x86_64-unknown-linux-gnu-gcc-9.0.0-alpha20181125 -march=core2 -O2
-fnon-call-exceptions -fschedule-insns -fselective-scheduling
-funroll-all-loops -fno-caller-saves -fno-guess-branch-probability -fno-ivopts
-fno-rerun-cse-after-loop -fno-split-wide-types -fno-tree-bit-ccp
-fno-tree-coalesce-vars --param max-completely-peeled-insns=13 -w -c ksb82gef.c
zsh: exit 124   timeout 10 x86_64-unknown-linux-gnu-gcc-9.0.0-alpha20181125
-march=core2 -O2

perf top:

 100.00%  cc1  [.] lra_split_hard_reg_for