[Bug rtl-optimization/41646] New: [4.3/4.4/4.5 Regression] Reload ICE due to combiner extending life time of a hard register

[jakub at gcc dot gnu dot org]

struct A { unsigned long a; };
struct B { unsigned short b, c, d; };
struct B bar (unsigned long);
char *
foo (char *a, struct A *x)
{
  struct B b = bar (x->a);
  unsigned char c;
  unsigned short d;
  a[3] = ((unsigned char) (b.b % 10) + 48);
  d = b.b / 10;
  a[2] = ((unsigned char) (d % 10) + 48);
  d = d / 10;
  a[1] = ((unsigned char) (d % 10) + 48);
  a[0] = ((unsigned char) ((d / 10) % 10) + 48);
  a[4] = 46;
  c = (unsigned char) b.c;
  a[6] = (c % 10 + 48);
  a[5] = ((c / 10) % 10 + 48);
  a[7] = 46;
  c = b.d;
  a[9] = (c % 10 + 48);
  a[8] = ((c / 10) % 10 + 48);
  return a + 10;
}

ICEs with -O2 on x86_64-linux:
/tmp/tt.c: In function 'foo':
/tmp/tt.c:25:1: error: unable to find a register to spill in class 'AREG'
/tmp/tt.c:25:1: error: this is the insn:
(insn 82 81 83 2 /tmp/tt.c:18 (parallel [
            (set (reg:HI 1 dx [170])
                (mult:HI (zero_extend:HI (reg/v:QI 4 si [orig:82 c ] [82]))
                    (zero_extend:HI (reg:QI 2 cx [169]))))
            (clobber (reg:CC 17 flags))
        ]) 337 {*umulqihi3_1} (expr_list:REG_UNUSED (reg:CC 17 flags)
        (expr_list:REG_EQUAL (mult:HI (zero_extend:HI (reg/v:QI 4 si [orig:82 c
] [82]))
                (const_int 205 [0xcd]))
            (nil))))
/tmp/tt.c:25:1: internal compiler error: in spill_failure, at reload1.c:2151
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://gcc.gnu.org/bugs.html> for instructions.

Worked in 3.4/4.0, ICEs from 4.1 onwards up to current trunk.

The problem seems to be in the combiner, it extremely lengthens the lifetime of
hard register (%rax):

in *.dce:
...
(insn 13 12 14 2 /tmp/tt.c:7 (parallel [
            (set (reg:DI 113)
                (lshiftrt:DI (reg:DI 0 ax)
                    (const_int 32 [0x20])))
            (clobber (reg:CC 17 flags))
        ]) 549 {*lshrdi3_1_rex64} (expr_list:REG_DEAD (reg:DI 0 ax)
        (expr_list:REG_UNUSED (reg:CC 17 flags)
            (nil))))
(insn 14 13 16 2 /tmp/tt.c:7 (set (reg:HI 114)
        (subreg:HI (reg:DI 113) 0)) 53 {*movhi_1} (expr_list:REG_DEAD (reg:DI
113)
        (nil)))
... 49 insns ...
(insn 82 81 83 2 /tmp/tt.c:18 (parallel [
            (set (reg:HI 168)
                (mult:HI (zero_extend:HI (reg/v:QI 82 [ c ]))
                    (zero_extend:HI (reg:QI 169))))
            (clobber (reg:CC 17 flags))
        ]) 337 {*umulqihi3_1} (expr_list:REG_UNUSED (reg:CC 17 flags)
        (expr_list:REG_EQUAL (mult:HI (zero_extend:HI (reg/v:QI 82 [ c ]))
                (const_int 205 [0xcd]))
            (nil))))
... 18 insns ...
(insn 108 107 110 2 /tmp/tt.c:21 (set (reg/v:QI 93 [ c ])
        (subreg:QI (reg:HI 114) 0)) 62 {*movqi_1} (expr_list:REG_DEAD (reg:HI
114)
        (nil)))
...
in *.combine:
...
(note 13 12 14 2 NOTE_INSN_DELETED)
(note 14 13 16 2 NOTE_INSN_DELETED)
... many insns ...
(insn 82 81 83 2 /tmp/tt.c:18 (parallel [
            (set (reg:HI 168)
                (mult:HI (zero_extend:HI (reg/v:QI 82 [ c ]))
                    (zero_extend:HI (reg:QI 169))))
            (clobber (reg:CC 17 flags))
        ]) 337 {*umulqihi3_1} (expr_list:REG_UNUSED (reg:CC 17 flags)
        (expr_list:REG_EQUAL (mult:HI (zero_extend:HI (reg/v:QI 82 [ c ]))
                (const_int 205 [0xcd]))
            (nil))))
... many insns ...
(insn 108 107 110 2 /tmp/tt.c:21 (parallel [
            (set (subreg:DI (reg/v:QI 93 [ c ]) 0)
                (lshiftrt:DI (reg:DI 0 ax)
                    (const_int 32 [0x20])))
            (clobber (reg:CC 17 flags))
        ]) 549 {*lshrdi3_1_rex64} (expr_list:REG_UNUSED (reg:CC 17 flags)
        (expr_list:REG_DEAD (reg:DI 0 ax)
            (nil))))
...


-- 
           Summary: [4.3/4.4/4.5 Regression] Reload ICE due to combiner
                    extending life time of a hard register
           Product: gcc
           Version: 4.4.1
            Status: UNCONFIRMED
          Keywords: ice-on-valid-code
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jakub at gcc dot gnu dot org
GCC target triplet: x86_64-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41646