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From: "hjl.tools at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/53772] New: Failed to combine load and jump on vtable
Date: Mon, 25 Jun 2012 21:59:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53772

             Bug #: 53772
           Summary: Failed to combine load and jump on vtable
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: hjl.tools@gmail.com
                CC: areg.melikadamyan@gmail.com, ubizjak@gmail.com
            Target: x86-64


[hjl@gnu-6 tmp]$ cat v.cc
struct Foo { virtual void f(); }; void f(Foo *f) { f->f(); }
[hjl@gnu-6 tmp]$ /opt/llvm/bin/clang -S -m64 -O2 -o clang64.s v.cc  
[hjl@gnu-6 tmp]$ cat clang64.s 
    .file    "v.cc"
    .text
    .globl    _Z1fP3Foo
    .align    16, 0x90
    .type    _Z1fP3Foo,@function
_Z1fP3Foo:                              # @_Z1fP3Foo
    .cfi_startproc
# BB#0:                                 # %entry
    movq    (%rdi), %rax
    jmpq    *(%rax)  # TAILCALL
.Ltmp0:
    .size    _Z1fP3Foo, .Ltmp0-_Z1fP3Foo
    .cfi_endproc


    .section    ".note.GNU-stack","",@progbits
[hjl@gnu-6 tmp]$ /usr/gcc-4.7.2-x32/bin/gcc -S -O2 -m64 v.cc -o gcc64.s  
[hjl@gnu-6 tmp]$ cat gcc64.s
    .file    "v.cc"
    .text
    .p2align 4,,15
    .globl    _Z1fP3Foo
    .type    _Z1fP3Foo, @function
_Z1fP3Foo:
.LFB0:
    .cfi_startproc
    movq    (%rdi), %rax
    movq    (%rax), %rax
    jmp    *%rax
    .cfi_endproc
.LFE0:
    .size    _Z1fP3Foo, .-_Z1fP3Foo
    .ident    "GCC: (GNU) 4.7.2 20120622 (prerelease)"
    .section    .note.GNU-stack,"",@progbits
[hjl@gnu-6 tmp]$