[Bug rtl-optimization/83494] New: [8 Regression] ICE: in assign_by_spills, at lra-assigns.c:1468: unable to find a register to spill with -flive-range-shrinkage

["zsojka at seznam dot cz" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83494

            Bug ID: 83494
           Summary: [8 Regression] ICE: in assign_by_spills, at
                    lra-assigns.c:1468: unable to find a register to spill
                    with -flive-range-shrinkage
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Keywords: ice-on-valid-code
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zsojka at seznam dot cz
  Target Milestone: ---
              Host: x86_64-pc-linux-gnu
            Target: x86_64-pc-linux-gnu

Created attachment 42922
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42922&action=edit
reduced testcase

Might be related or duplicate PR83467, but this one does not need any
target-specific flags.

Compiler output:
$ x86_64-pc-linux-gnu-gcc -O2 -flive-range-shrinkage testcase.c
testcase.c: In function 'a':
testcase.c:8:1: error: unable to find a register to spill
 }
 ^
testcase.c:8:1: error: this is the insn:
(insn 46 49 6 2 (parallel [
            (set (reg:SI 115 [ d ])
                (ashift:SI (reg/v:SI 106 [ d ])
                    (reg:QI 125 [ f ])))
            (clobber (reg:CC 17 flags))
        ]) "testcase.c":3 540 {*ashlsi3_1}
     (expr_list:REG_DEAD (reg:QI 125 [ f ])
        (expr_list:REG_DEAD (reg/v:SI 106 [ d ])
            (expr_list:REG_UNUSED (reg:CC 17 flags)
                (nil)))))
during RTL pass: reload
testcase.c:8:1: internal compiler error: in assign_by_spills, at
lra-assigns.c:1468
0x696c9a _fatal_insn(char const*, rtx_def const*, char const*, int, char
const*)
        /repo/gcc-trunk/gcc/rtl-error.c:108
0xcf7fba assign_by_spills
        /repo/gcc-trunk/gcc/lra-assigns.c:1468
0xcf8b1c lra_assign()
        /repo/gcc-trunk/gcc/lra-assigns.c:1662
0xcf3404 lra(_IO_FILE*)
        /repo/gcc-trunk/gcc/lra.c:2469
0xca0d99 do_reload
        /repo/gcc-trunk/gcc/ira.c:5443
0xca0d99 execute
        /repo/gcc-trunk/gcc/ira.c:5627
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.

$ x86_64-pc-linux-gnu-gcc -v
Using built-in specs.
COLLECT_GCC=/repo/gcc-trunk/binary-latest-amd64/bin/x86_64-pc-linux-gnu-gcc
COLLECT_LTO_WRAPPER=/repo/gcc-trunk/binary-trunk-255786-checking-yes-rtl-df-extra-nographite-amd64/bin/../libexec/gcc/x86_64-pc-linux-gnu/8.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /repo/gcc-trunk//configure --enable-languages=c,c++
--enable-valgrind-annotations --disable-nls --enable-checking=yes,rtl,df,extra
--without-cloog --without-ppl --without-isl --build=x86_64-pc-linux-gnu
--host=x86_64-pc-linux-gnu --target=x86_64-pc-linux-gnu
--with-ld=/usr/bin/x86_64-pc-linux-gnu-ld
--with-as=/usr/bin/x86_64-pc-linux-gnu-as --disable-libstdcxx-pch
--prefix=/repo/gcc-trunk//binary-trunk-255786-checking-yes-rtl-df-extra-nographite-amd64
Thread model: posix
gcc version 8.0.0 20171218 (experimental) (GCC)