[Bug rtl-optimization/50891] New: move2add_note_store fails to properly track register content

[hjl.tools at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50891

             Bug #: 50891
           Summary: move2add_note_store fails to properly track register
                    content
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: hjl.to...@gmail.com


There are

(insn 18 323 318 2 (set (reg:DI 2 cx [orig:110 MEM[(c_char * {ref-all})&A.0]+8
] [110])
        (mem/s/u/c:DI (const:SI (plus:SI (symbol_ref:SI ("A.0.1724") [flags
0x2] <var_decl 0x7ffff1435460 A.0>)
                    (const_int 8 [0x8]))) [0 MEM[(c_char * {ref-all})&A.0]+8 S8
A64])) x.f90:7 62 {*movdi_internal_rex64}
     (expr_list:REG_EQUIV (mem/s/u/c:DI (const:SI (plus:SI (symbol_ref:SI
("A.0.1724") [flags 0x2] <var_decl 0x7ffff1435460 A.0>)
                    (const_int 8 [0x8]))) [0 MEM[(c_char * {ref-all})&A.0]+8 S8
A64])
        (nil)))
....
(insn 73 71 74 11 (set (reg:SI 2 cx [125])
        (const_int 16 [0x10])) x.f90:12 64 {*movsi_internal}
     (expr_list:REG_EQUAL (const_int 16 [0x10])
        (nil)))

For some reason, move2add_use_add2_insn replaces it with

(insn 73 71 74 11 (set (strict_low_part (reg:QI 2 cx)) 
        (const_int 16 [0x10])) x.f90:12 81 {*movstrictqi_1}
     (expr_list:REG_EQUAL (const_int 16 [0x10])
        (nil)))

The problem is the upper 48bits of CX isn't zero.