[Bug bootstrap/39454] New: [4.4 Regression] Bootstrap failure on sparcv9-linux with profiledbootstrap

["jakub at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

Unfortunately only during profiledbootstrap I see a bootstrap failure on
sparcv9-linux, the ICEs look like:
error: unrecognizable insn:
(insn 86 30 87 6 /tmp/ccxt3Axa.out:5527 (set (reg:SI 24 %i0)
        (and:SI (reg:SI 24 %i0 [ u ])
            (const_int -65281 [0xffffffffffff00ff]))) -1 (nil))
/tmp/ccxt3Axa.out:5537: internal compiler error: in extract_insn, at
recog.c:2038

Turns out this is because of miscompiled simplify_subreg (particularly
simplify_immed_subreg inlined into it) when compiled with -fprofile-use.
debug_rtx (simplify_subreg (SImode, gen_int_mode (0x3ffffffffffffeULL, DImode),
DImode, 0))
shows this, prints (const_int 0x3f00ff) instead of (const_int 0x3fffff).

The problem is in handling out of range shifts.  SPARC is SHIFT_COUNT_TRUNCATED
target, so when expanding a DImode shift in 32-bit mode, the shift counts (in
this case going from 0 to 56 in steps of 8) aren't masked in any way, we have
(insn 385 384 386 ../../gcc/simplify-rtx.c:4718 (set (subreg:SI (reg:DI 420) 0)
(ashiftrt:SI (reg:SI 429) (reg/v:SI 160 [ i.2321 ]))) -
1 (nil))
etc. after expansion where pseudo 160 goes from 0 to 56 in steps of 8.
Later on loop unrolling unrolls this and then CSE2 for one of the shifts
determines the shift count is 40, but due to a bug leaves it as non-canonical
(insn 3290 3283 3291 332 ../../gcc/simplify-rtx.c:4718 (set (reg:SI 1368)
        (ashiftrt:SI (reg:SI 1361 [ <variable>.u.hwint ])
            (const_int 40 [0x28]))) 358 {ashrsi3} (expr_list:REG_DEAD (reg:SI
425 [ <variable>.u.hwint ])
        (nil)))

Then during combine:
(insn 3283 3305 3290 354 ../../gcc/simplify-rtx.c:4718 (set (reg:SI 1361 [
<variable>.u.hwint ])
        (mem/s:SI (plus:SI (reg/v/f:SI 240 [ el ])
                (const_int 8 [0x8])) [0 <variable>.u.hwint+0 S4 A64])) 50
{*movsi_insn} (nil))

(insn 3290 3283 3293 354 ../../gcc/simplify-rtx.c:4718 (set (reg:SI 1368)
        (ashiftrt:SI (reg:SI 1361 [ <variable>.u.hwint ])
            (const_int 40 [0x28]))) 358 {ashrsi3} (expr_list:REG_DEAD (reg:SI
1361 [ <variable>.u.hwint ])
        (nil)))

(insn 3293 3290 3294 354 ../../gcc/simplify-rtx.c:4718 (set (mem:QI (plus:SI
(reg/f:SI 1213)
                (const_int 4 [0x4])) [0 S1 A8])
        (subreg:QI (reg:SI 1368) 3)) 47 {*movqi_insn} (expr_list:REG_DEAD
(reg:SI 1368)
        (expr_list:REG_DEAD (reg/v/f:SI 161 [ vp.2320 ])
            (nil))))
is optimized into a store of (const_int 0), because nonzero_bits says so.


-- 
           Summary: [4.4 Regression] Bootstrap failure on sparcv9-linux with
                    profiledbootstrap
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: bootstrap
        AssignedTo: jakub at gcc dot gnu dot org
        ReportedBy: jakub at gcc dot gnu dot org
GCC target triplet: sparcv9-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39454