[Bug c/43599] New: Several missing optimizations

["piotr dot wyderski at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

I was wondering whether GCC can optimize
sin(x) and cos(x) of the same angle in order
to use the combined fsincos x86 instruction.
The testcase is:

----------------8<--------------------

#include <math.h>

double fn1(double x) {

    return sin(x) * cos(x);
}

double fn2(double x) {

    return __builtin_sin(x) * __builtin_cos(x);
}

----------------8<--------------------

I compile it with:

gcc -O3 -fomit-frame-pointer -S testcase.cpp

The result turned out to be rather surprising:

----------------8<--------------------

        .file   "testcase.cpp"
        .text
        .p2align 4,,15
.globl __Z3fn1d
        .def    __Z3fn1d;       .scl    2;      .type   32;     .endef
__Z3fn1d:
        subl    $60, %esp
        fldl    64(%esp)
        fstl    (%esp)
        fstpl   16(%esp)
        call    _sin
        fstpl   40(%esp)
        fldl    16(%esp)
        fstpl   (%esp)
        call    _cos
        fmull   40(%esp)
        addl    $60, %esp
        ret
        .p2align 4,,15
.globl __Z3fn2d
        .def    __Z3fn2d;       .scl    2;      .type   32;     .endef
__Z3fn2d:
        subl    $60, %esp
        fldl    64(%esp)
        fstl    (%esp)
        fstpl   16(%esp)
        call    _sin
        fstpl   40(%esp)
        fldl    16(%esp)
        fstpl   (%esp)
        call    _cos
        fmull   40(%esp)
        addl    $60, %esp
        ret
        .def    _sin;   .scl    2;      .type   32;     .endef
        .def    _cos;   .scl    2;      .type   32;     .endef
        .def    _sin;   .scl    2;      .type   32;     .endef
        .def    _cos;   .scl    2;      .type   32;     .endef 

----------------8<--------------------

As you can see:

a) fsin and fcos are not combined into fsincos, because
b) there are no fsin and fcos -- library calls have been emitted;
c) the stack top manipulation (subl / addl $60, %esp) has no purpose.


-- 
           Summary: Several missing optimizations
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: piotr dot wyderski at gmail dot com
 GCC build triplet: i686-pc-cygwin
  GCC host triplet: i686-pc-cygwin
GCC target triplet: i686-pc-cygwin


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43599