[Bug rtl-optimization/57130] New: Incorrect "and --> extract" conversion in combine

["wmi at google dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57130

             Bug #: 57130
           Summary: Incorrect "and --> extract" conversion in combine
    Classification: Unclassified
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: wmi@google.com


Created attachment 29986
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29986
Testcase

For the smallcase 1.ii attached.

~/workarea/gcc-r198433/build/install/bin/g++ 1.ii -o a1.out
./a1.out  --> correct output:
1
3

~/workarea/gcc-r198433/build/install/bin/g++ -fno-inline
-fno-omit-frame-pointer -O2 1.ii -o a2.out
./a2.out  --> incorrect output:
1
-1

In 1.ii.196r.ud_dce:

(insn 7 2 84 2 (set (reg:DI 64)
        (const_int -4294967296 [0xffffffff00000000])) 1.ii:26 84
{*movdi_internal}
     (nil))
...
(insn 40 36 44 2 (parallel [
            (set (reg:DI 88)
                (and:DI (reg:DI 80)
                    (reg:DI 64)))
            (clobber (reg:CC 17 flags))
        ]) 1.ii:32 386 {*anddi_1}
     (expr_list:REG_DEAD (reg:DI 80)
        (expr_list:REG_DEAD (reg:DI 64)
            (expr_list:REG_UNUSED (reg:CC 17 flags)
                (expr_list:REG_EQUAL (and:DI (reg:DI 80)
                        (const_int -4294967296 [0xffffffff00000000]))
                    (nil))))))
(insn 44 40 45 2 (set (reg:DI 92 [ mini_rect ])
        (zero_extend:DI (subreg:SI (reg:DI 88) 0))) 1.ii:33 127
{*zero_extendsidi2}
     (expr_list:REG_DEAD (reg:DI 88)
        (nil)))

The value of r92 here should always be 0.

After try_combine with params (i3==insn44, i2==insn40, i1==insn7), insn44 is
transformed to: 
(insn 44 40 45 2 (parallel [
            (set (reg:DI 92 [ mini_rect ])
                (ashiftrt:DI (reg:DI 88)
                    (const_int 63 [0x3f])))
            (clobber (reg:CC 17 flags))
        ]) 1.ii:33 528 {ashrdi3_cvt}
     (expr_list:REG_UNUSED (reg:CC 17 flags)
        (expr_list:REG_DEAD (reg:DI 88)
            (nil))))

The value of r92 now equals either 0 or -1 which depends on the highest bit of
r88. 

Try to understand what happen in try_combine:
In try_combine, after subst(PATTERN (i3), i2dest, i2src, ...), insn 44 is
transformed to the following form. This step is correct. 

(insn 44 40 45 2 (set (reg:DI 92 [ mini_rect ])
        (neg:DI (ne:DI (subreg:SI (and:DI (reg:DI 80)
                        (reg:DI 64)) 0)
                (const_int 0 [0])))) 1.ii:33 127 {*zero_extendsidi2}
     (expr_list:REG_DEAD (reg:DI 88)
        (nil)))

In subst(PATTERN (i3), i1dest, i1src, ...), insn 44 is firstly transformed to
the following in simplify_logical, which is correct:

(insn 44 40 45 2 (set (reg:DI 92 [ mini_rect ])
        (neg:DI (ne:DI (subreg:SI ((and:DI (reg:DI 80)
                        (const_int 34359738368 [0x800000000]))) 0)
                (const_int 0 [0])))) 1.ii:33 127 {*zero_extendsidi2}
     (expr_list:REG_DEAD (reg:DI 88)
        (nil)))

then it is transformed to the following in make_compound_operation, which is
incorrect:

(insn 44 40 45 2 (set (reg:DI 92 [ mini_rect ])
        (sign_extract:DI (reg:DI 80)
            (const_int 1 [0x1])
            (const_int 35 [0x23]))) 1.ii:33 127 {*zero_extendsidi2}
     (expr_list:REG_DEAD (reg:DI 88)
        (nil)))


make_compound_operation transforms

(and:DI (reg:DI 80)
    (const_int 34359738368 [0x800000000]))

to

(zero_extract:DI (reg:DI 80)
    (const_int 1 [0x1])
    (const_int 35 [0x23]))

because it thinks the "and expr" here is in a compare. But actually the "and
expr" is firstly the kid in a subreg: 

subreg:SI ((and:DI (reg:DI 80)
    (const_int 34359738368 [0x800000000]))  ==> always 0

is not identical with

subreg:SI ((zero_extract:DI (reg:DI 80)
    (const_int 1 [0x1])
    (const_int 35 [0x23]))      ==> 0 or 1

So it is the cause of the problem. The second actual of make_compound_operation
(combine.c:7701, r198433) should not be in_code.