[Bug rtl-optimization/68330] New: [6 Regression]: FAIL: gcc.target/alpha/pr42269-1.c scan-assembler-not addl on alpha-linux-gnu

[ubizjak at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68330

            Bug ID: 68330
           Summary: [6 Regression]: FAIL: gcc.target/alpha/pr42269-1.c
                    scan-assembler-not addl on alpha-linux-gnu
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ubizjak at gmail dot com
  Target Milestone: ---
            Target: alpha-linux-gnu

Revision r230164 [1] regressed:

FAIL: gcc.target/alpha/pr42269-1.c scan-assembler-not addl

on alpha-linux-gnu.

The difference starts in combine, where before the patch, we were able
to combine insns:

(insn 7 6 8 2 (set (reg:DI 82)
        (lshiftrt:DI (reg:DI 81 [ x ])
            (const_int 16 [0x10]))) pr42269-1.c:8 66 {lshrdi3}
     (expr_list:REG_DEAD (reg:DI 81 [ x ])
        (nil)))
(insn 8 7 11 2 (set (reg:DI 70 [ _2 ])
        (sign_extend:DI (subreg:SI (reg:DI 82) 0))) pr42269-1.c:8 2
{*extendsidi2_1}
     (expr_list:REG_DEAD (reg:DI 82)
        (nil)))

to:

Trying 7 -> 8:
Successfully matched this instruction:
(set (reg:DI 70 [ _2 ])
    (zero_extract:DI (reg/v:DI 80 [ x ])
        (const_int 16 [0x10])
        (const_int 16 [0x10])))
allowing combination of insns 7 and 8
original costs 4 + 4 = 8
replacement cost 4
deferring deletion of insn with uid = 7.
modifying insn i3     8: r70:DI=zero_extract(r80:DI,0x10,0x10)
deferring rescan insn with uid = 8.

After the patch, the combination fails:

Trying 7 -> 8:
Failed to match this instruction:
(set (reg:DI 70 [ _2 ])
    (sign_extend:DI (lshiftrt:SI (subreg:SI (reg/v:DI 80 [ x ]) 0)
            (const_int 16 [0x10]))))

[1] https://gcc.gnu.org/ml/gcc-patches/2015-11/msg00900.html