[Bug c++/30738] New: suboptimal code for min, max, et al

[sebor at roguewave dot com]

For T being an arithmetic type, gcc 4.1 generates what looks like suboptimal
assembly code for inline C++ functions that take their argument(s) by const
reference (const T&) vs the same functions that take their argument(s) by value
(T).

Ideally, the code generated for test_min_ref() and test_min_ptr() below would
be the same as for test_min_val(). The code generated for SPARC at the bottom
shows that the code for both functions is worse.

template <class T> inline const T& min_ref (const T &x, const T &y) { return x
< y ? x : y; }
template <class T> inline const T* min_ptr (const T *x, const T *y) { return *x
< *y ? x : y; }
template <class T> inline T min_val (T x, T y) { return x < y ? x : y; }
int test_min_ref (int x, int y) { return min_ref (x, y); }
int test_min_ptr (int x, int y) { return *min_ptr (&x, &y); }
int test_min_val (int x, int y) { return min_val (x, y); }

        .file   "t.cpp"
        .section        ".text"
        .align 4
        .global _Z12test_min_refii
        .type   _Z12test_min_refii, #function
        .proc   04
_Z12test_min_refii:
.LLFB5:
        cmp     %o0, %o1
        st      %o0, [%sp+68]
        st      %o1, [%sp+72]
        bge     .LL7
         add    %sp, 68, %o0
        jmp     %o7+8
         ld     [%o0], %o0
.LL7:
        add     %sp, 72, %o0
        jmp     %o7+8
         ld     [%o0], %o0
.LLFE5:
        .size   _Z12test_min_refii, .-_Z12test_min_refii
        .global __gxx_personality_v0
        .align 4
        .global _Z12test_min_ptrii
        .type   _Z12test_min_ptrii, #function
        .proc   04
_Z12test_min_ptrii:
.LLFB6:
        cmp     %o0, %o1
        st      %o0, [%sp+68]
        st      %o1, [%sp+72]
        bge     .LL13
         add    %sp, 68, %o0
        jmp     %o7+8
         ld     [%o0], %o0
.LL13:
        add     %sp, 72, %o0
        jmp     %o7+8
         ld     [%o0], %o0
.LLFE6:
        .size   _Z12test_min_ptrii, .-_Z12test_min_ptrii
        .align 4
        .global _Z12test_min_valii
        .type   _Z12test_min_valii, #function
        .proc   04
_Z12test_min_valii:
.LLFB7:
        cmp     %o0, %o1
        bg,a    .LL17
         mov    %o1, %o0
.LL17:
        jmp     %o7+8
         nop
.LLFE7:
        .size   _Z12test_min_valii, .-_Z12test_min_valii
        .ident  "GCC: (GNU) 4.1.0"


-- 
           Summary: suboptimal code for min, max, et al
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: sebor at roguewave dot com
 GCC build triplet: sparc-sun-solaris
  GCC host triplet: sparc-sun-solaris
GCC target triplet: sparc-sun-solaris


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30738