Attachment 1322692 Details for Bug 1488993 – foo.cpp

foo.cpp

foo.cpp (text/x-csrc), 1.33 KB, created by Paulo Andrade on 2017-09-06 14:51:38 UTC

(hide)

Description:

Filename:

MIME Type:

Creator: Paulo Andrade

Created: 2017-09-06 14:51:38 UTC

Size: 1.33 KB

patch

obsolete

>// This example exposes an optimizer bug in GCC on RHEL 7.2,
>// g++ (GCC) 4.8.5 20150623 (Red Hat 4.8.5-4).
>//
>// When compiled with
>//
>//   g++ --std=c++11 -O2 -S foo.cpp
>//
>// the generated code for the loop is as expected:
>//
>//   .L4:
>//         leaq    15(%rsp), %rdi
>//         movl    %ebx, %esi
>//         addl    $1, %ebx
>//         call    Derived::fun(int) const
>//         cmpl    %ebp, %eax
>//         je      .L2
>//         call    zonk()
>//   .L2:
>//         addl    $286331153, %ebp
>//         cmpl    $8, %ebx
>//         jne     .L4
>//
>// When compiled with
>//
>//   g++ --std=c++11 -O2 -DBUG -S foo.cpp
>//
>// the loop condition disappears, making the loop infinite:
>//
>//   .L5:
>//         movl    %ebx, %esi
>//         movq    %rsp, %rdi
>//   .LEHB1:
>//         call    Derived::fun(int) const
>//         addl    $1, %ebx
>//         cmpl    %ebp, %eax
>//         je      .L7
>//         call    zonk()
>//   .LEHE1:
>//   .L7:
>//         addl    $286331153, %ebp
>//         jmp     .L5                      INFINITE LOOP
>
>class Base
>{
>public:
>#ifdef BUG
>  virtual ~Base(void);
>#endif
>};
>
>class Derived : public Base
>{
>public:
>  int fun(int) const;
>};
>
>extern Derived oink(void);
>extern void zonk(void);
>
>void
>foo(void)
>{
>  Derived rsp = oink();
>
>  for (int i = 0; i < 8; ++i) {
>    if (rsp.fun(i) != (0x11111111 * (i+1))) {
>      zonk();
>    }
>  }
>}

Actions: View

Attachments on bug 1488993: 1322692